fix(canvas): retain canonical frame rotation across owner changes

Reviewed-on: #18

.gitea/workflows/check.yml

@@ -4,7 +4,8 @@ on: [push, pull_request]
 jobs:
   check:
     runs-on: ces-control
-    timeout-minutes: 10
+    # Cold toolchain installation can exceed ten minutes on the existing runner.
+    timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
@@ -68,8 +69,19 @@ jobs:
               print("Negative control result:", control if control in known else "unclassified")
               sys.exit("Slack client preflight could not verify the configured credentials")
           PYSLACK
-      - name: Verify schema migration in an isolated database
-        run: bash deploy/check-schema.sh
+      - name: Fetch pinned headless HTTP integration client
+        env:
+          HEADLESS_CLIENT_REVISION: dcbbdad25de7c3b1d6bee317df6074da2c0642eb
+        run: |
+          set -eu
+          mkdir -p .headless-client
+          curl --fail --silent --show-error --location \
+            "https://gitea.entroia.com/Zayden-Jung/Endoleap/archive/$HEADLESS_CLIENT_REVISION.tar.gz" \
+            | tar -xz --strip-components=1 -C .headless-client
+          test -f .headless-client/tests/headless/foundry.integration.mjs
+          printf 'Pinned Endoleap client: %s\n' "$HEADLESS_CLIENT_REVISION"
+      - name: Verify schema migration and real headless HTTP client in an isolated database
+        run: HEADLESS_CLIENT_SOURCE="$PWD/.headless-client" bash deploy/check-schema.sh
       - name: Smoke test HTTP routes
         env:
           PUBLIC_ORIGIN: https://api.example.com

db/008-canvas-model.sql

@@ -0,0 +1,103 @@
+BEGIN;
+-- Canonical rows are separate from the legacy snapshot. Adoption is an explicit,
+-- version-checked transaction; installing this schema does not migrate user data.
+CREATE TABLE canvas_model_projects (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ root_id uuid NOT NULL,
+ document_format_version integer NOT NULL DEFAULT 1 CHECK(document_format_version=1),
+ migration_id uuid NOT NULL,
+ source_versions jsonb NOT NULL,
+ created_at timestamptz NOT NULL DEFAULT now(),
+ PRIMARY KEY(project,workspace_id,root_id),
+ FOREIGN KEY(project,workspace_id,root_id) REFERENCES materials ON DELETE CASCADE
+);
+CREATE TABLE canvas_model_canvases (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ root_id uuid NOT NULL,
+ canvas_id uuid NOT NULL,
+ parent_canvas_id uuid,
+ entry_element_id text,
+ version bigint NOT NULL CHECK(version>0),
+ archived boolean NOT NULL DEFAULT false,
+ PRIMARY KEY(project,workspace_id,canvas_id),
+ UNIQUE(project,canvas_id),
+ UNIQUE(project,workspace_id,root_id,canvas_id),
+ CHECK((parent_canvas_id IS NULL)=(entry_element_id IS NULL)),
+ CHECK(parent_canvas_id IS NOT NULL OR canvas_id=root_id),
+ FOREIGN KEY(project,workspace_id,root_id) REFERENCES canvas_model_projects ON DELETE CASCADE,
+ FOREIGN KEY(project,workspace_id,canvas_id) REFERENCES materials ON DELETE CASCADE,
+ FOREIGN KEY(project,workspace_id,root_id,parent_canvas_id) REFERENCES canvas_model_canvases(project,workspace_id,root_id,canvas_id) DEFERRABLE INITIALLY DEFERRED
+);
+CREATE UNIQUE INDEX canvas_model_active_entry ON canvas_model_canvases(project,workspace_id,entry_element_id) WHERE NOT archived;
+CREATE TABLE canvas_model_elements (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ root_id uuid NOT NULL,
+ element_id text NOT NULL CHECK(element_id ~ '^[A-Za-z0-9_-]{1,128}$'),
+ owner_canvas_id uuid NOT NULL,
+ incarnation bigint NOT NULL CHECK(incarnation>0 AND incarnation<=9007199254740991),
+ deleted_incarnation bigint NOT NULL DEFAULT 0 CHECK(deleted_incarnation>=0 AND deleted_incarnation<=incarnation),
+ record jsonb NOT NULL,
+ deleted boolean NOT NULL DEFAULT false,
+ PRIMARY KEY(project,element_id),
+ UNIQUE(project,workspace_id,element_id),
+ CHECK(jsonb_typeof(record)='object' AND record->>'id'=element_id AND record->>'ownerCanvasId'=owner_canvas_id::text AND (record->>'incarnation')::bigint=incarnation),
+ CHECK(NOT deleted OR deleted_incarnation=incarnation),
+ FOREIGN KEY(project,workspace_id,root_id) REFERENCES canvas_model_projects ON DELETE CASCADE,
+ FOREIGN KEY(project,workspace_id,root_id,owner_canvas_id) REFERENCES canvas_model_canvases(project,workspace_id,root_id,canvas_id) DEFERRABLE INITIALLY DEFERRED
+);
+CREATE INDEX canvas_model_owner ON canvas_model_elements(project,workspace_id,root_id,owner_canvas_id) WHERE NOT deleted;
+ALTER TABLE canvas_model_canvases ADD CONSTRAINT canvas_model_entry_fk FOREIGN KEY(project,workspace_id,entry_element_id) REFERENCES canvas_model_elements(project,workspace_id,element_id) DEFERRABLE INITIALLY DEFERRED;
+CREATE TABLE canvas_model_identity_map (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ root_id uuid NOT NULL,
+ source_canvas_id uuid NOT NULL,
+ source_structure text NOT NULL CHECK(source_structure IN('node','connection')),
+ source_element_id text NOT NULL,
+ element_id text NOT NULL,
+ PRIMARY KEY(project,workspace_id,root_id,source_canvas_id,source_structure,source_element_id),
+ UNIQUE(project,element_id),
+ FOREIGN KEY(project,workspace_id,root_id) REFERENCES canvas_model_projects ON DELETE CASCADE,
+ FOREIGN KEY(project,workspace_id,element_id) REFERENCES canvas_model_elements(project,workspace_id,element_id) DEFERRABLE INITIALLY DEFERRED
+);
+-- Logical operations cannot acquire a second successful execution under a new request key.
+CREATE TABLE canvas_model_requests (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ account_id uuid NOT NULL,
+ request_id uuid NOT NULL,
+ root_id uuid NOT NULL,
+ action text NOT NULL,
+ protocol_version integer NOT NULL,
+ payload_hash text NOT NULL,
+ response_status integer NOT NULL,
+ response_body jsonb NOT NULL,
+ created_at timestamptz NOT NULL DEFAULT now(),
+ PRIMARY KEY(project,workspace_id,account_id,request_id),
+ FOREIGN KEY(project,workspace_id,root_id) REFERENCES materials ON DELETE RESTRICT,
+ FOREIGN KEY(project,account_id) REFERENCES project_accounts
+);
+CREATE TABLE canvas_model_operations (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ operation_id uuid NOT NULL,
+ request_id uuid NOT NULL,
+ account_id uuid NOT NULL,
+ PRIMARY KEY(project,workspace_id,operation_id),
+ FOREIGN KEY(project,workspace_id,account_id,request_id) REFERENCES canvas_model_requests DEFERRABLE INITIALLY DEFERRED,
+ FOREIGN KEY(project,account_id) REFERENCES project_accounts
+);
+CREATE FUNCTION foundry_guard_canonical_canvas() RETURNS trigger LANGUAGE plpgsql AS $$
+BEGIN
+ IF (NEW.canvas_document IS DISTINCT FROM OLD.canvas_document OR NEW.canvas_version IS DISTINCT FROM OLD.canvas_version)
+ AND EXISTS(SELECT 1 FROM canvas_model_canvases c WHERE c.project=NEW.project AND c.workspace_id=NEW.workspace_id AND c.canvas_id=NEW.id)
+ AND current_setting('foundry.canonical_writer',true) IS DISTINCT FROM 'on' THEN
+  RAISE EXCEPTION 'canonical_write_required' USING ERRCODE='55000';
+ END IF;
+ RETURN NEW;
+END $$;
+CREATE TRIGGER canonical_canvas_write_barrier BEFORE UPDATE OF canvas_document,canvas_version ON materials FOR EACH ROW EXECUTE FUNCTION foundry_guard_canonical_canvas();
+COMMIT;

db/009-canvas-ai-operations.sql

@@ -0,0 +1,6 @@
+BEGIN;
+-- Legacy requests retain NULL. Canonical operation identity cannot be replayed
+-- under another transport key to admit a second paid execution.
+ALTER TABLE canvas_ai_runs ADD COLUMN logical_operation_id uuid;
+CREATE UNIQUE INDEX canvas_ai_logical_operation ON canvas_ai_runs(project,workspace_id,account_id,logical_operation_id) WHERE logical_operation_id IS NOT NULL;
+COMMIT;

db/010-canvas-ai-receipts.sql

@@ -0,0 +1,29 @@
+BEGIN;
+-- Keep transport receipts independently from execution retention. Their absence
+-- must never be used as proof that a paid invocation did not happen.
+CREATE TABLE canvas_ai_requests (
+ project text NOT NULL,
+ workspace_id uuid NOT NULL,
+ account_id uuid NOT NULL,
+ request_id uuid NOT NULL,
+ board_id uuid NOT NULL,
+ run_id uuid,
+ action text NOT NULL CHECK(action IN('run.start','run.cancel','run.apply')),
+ operation_id uuid NOT NULL,
+ payload_hash text NOT NULL,
+ outcome text NOT NULL CHECK(outcome IN('applied','not-applied')),
+ response_status integer NOT NULL,
+ response_body jsonb NOT NULL,
+ created_at timestamptz NOT NULL DEFAULT now(),
+ PRIMARY KEY(project,workspace_id,account_id,request_id),
+ FOREIGN KEY(project,workspace_id) REFERENCES workspaces(project,id) ON DELETE CASCADE
+);
+-- A known zero-effect rejection may be explicitly replanned under another key;
+-- a completed logical action must never execute twice under different keys.
+CREATE UNIQUE INDEX canvas_ai_request_operation ON canvas_ai_requests(project,workspace_id,account_id,operation_id) WHERE outcome='applied';
+-- Preserve accepted canonical requests that predate this receipt table.
+INSERT INTO canvas_ai_requests(project,workspace_id,account_id,request_id,board_id,action,operation_id,payload_hash,outcome,response_status,response_body)
+SELECT project,workspace_id,account_id,idempotency_key,board_id,'run.start',logical_operation_id,payload_hash,'applied',202,create_response
+FROM canvas_ai_runs WHERE logical_operation_id IS NOT NULL AND create_response->>'protocol_version'='2'
+ORDER BY created_at,id ON CONFLICT DO NOTHING;
+COMMIT;

db/011-canvas-ai-target-location.sql

@@ -0,0 +1,9 @@
+BEGIN;
+-- The frozen board remains the plan origin; result versions belong to the board
+-- that actually received the output after any owner-only move.
+ALTER TABLE canvas_ai_steps ADD COLUMN applied_board_id uuid;
+ALTER TABLE canvas_ai_steps ADD FOREIGN KEY(project,workspace_id,applied_board_id) REFERENCES materials(project,workspace_id,id);
+UPDATE canvas_ai_steps SET applied_board_id=board_id WHERE applied_version IS NOT NULL;
+CREATE UNIQUE INDEX canvas_ai_canonical_target_busy ON canvas_ai_steps(project,workspace_id,(frozen_input->>'canonical_root'),node_id,(frozen_input->>'target_incarnation'))
+ WHERE status IN('queued','running') AND frozen_input->>'canonical_root' IS NOT NULL;
+COMMIT;

deploy/check-schema.sh

@@ -78,3 +78,18 @@ for package in platform auth research; do
     -e RESEARCH_TEST_DATABASE_URL=postgres://foundry_research_fixture@127.0.0.1:5432/postgres?sslmode=disable \
     --entrypoint /opt/integration-tests postgres:17-alpine -test.v
 done
+
+# Run the actual pinned Endoleap runtime against this build's authenticated HTTP
+# routes and the same disposable database. Only this remote container needs Node.
+if [[ -n "${HEADLESS_CLIENT_SOURCE:-}" ]]; then
+  test -f "$HEADLESS_CLIENT_SOURCE/tests/headless/foundry.integration.mjs"
+  docker run --rm --network "container:$container" --user 1000:1000 \
+    --read-only --cap-drop ALL --security-opt no-new-privileges \
+    --tmpfs /tmp:rw,nosuid,nodev,noexec,size=32m,mode=1777 \
+    --mount "type=bind,source=$(pwd)/bin/platform-tests,target=/opt/integration-tests,readonly" \
+    --mount "type=bind,source=$HEADLESS_CLIENT_SOURCE,target=/opt/headless-client,readonly" \
+    -e PLATFORM_TEST_DATABASE_URL=postgres://foundry_fixture@127.0.0.1:5432/postgres?sslmode=disable \
+    -e FOUNDRY_HEADLESS_SOURCE=/opt/headless-client \
+    --entrypoint /opt/integration-tests node:24-bookworm-slim \
+    -test.v -test.run '^TestHeadlessClientHTTPIntegration$' -test.timeout 3m
+fi

docs/research-api.md

@@ -46,7 +46,8 @@ not require a session; these routes do not expose private data or accept writes.
 
 List parameters are `q` (200 Unicode characters, 20 words), `searchIn`
 (`text` or `author`), `topic` (an exact arXiv category), `sort` (`recent` or
-`title`), `page` (1–1000), and `pageSize` (1–50, default 8). Unknown, malformed
+`title`), `cursor` (optional, opaque, at most 32768 characters), and
+`pageSize` (1–50, default 8). Unknown, malformed
 or repeated parameters return 400. `recent` means descending stable paper ID,
 not publication date. Search terms must become bound query parameters, never
 raw SQL or user-supplied full-text syntax.
@@ -61,17 +62,35 @@ those two missing access paths. It is separate from Core startup and auth
 migrations; do not grant DDL to the runtime reader. Both indexes completed on the confirmed ECS (category 35.4 seconds, author
 436.47 seconds); measured end-to-end checks are documented below.
 
-List responses contain `items`, `total`, `topics`, `page`, and `pageSize`.
+List responses contain `items`, `nextCursor`, `previousCursor`, `topics`, and
+`pageSize`. Empty cursor strings mean that direction is unavailable. There is
+no `total`, page number, total page count or deep-page cap. The old `page`
+parameter is rejected; coordinate the frontend/backend contract update.
 Each paper preserves original title/abstract, authors, source dates, topics and
 source links. Publication decisions need source evidence; absent decisions stay
 unknown. No invented repositories, metrics or generated research conclusions.
 
-The repository counts and reads each list in one read-only snapshot.
-Paging first materializes matching IDs, then joins only that page to the wide
-paper rows. Filtered searches first materialize matching IDs without an
-ORDER BY/LIMIT, then sort/page those IDs, preventing sparse terms from choosing
-a backward heap scan with repeated text-vector computation. Activity sampling showed that selecting full rows before LIMIT
-caused sparse category queries to read large portions of the paper heap. The
+Lists use a read-only repeatable-read snapshot without `count(*)` or `OFFSET`.
+Keyset paging uses ID descending for recent order and `(title_key, id)` ascending
+for title order, including a reverse query for previous pages. The title key is
+kept in its stored codec and C collation. Cursors bind normalized query, search
+scope, topic, sort and page size; changing filters requires a fresh cursor. They
+are public row positions, not authorization tokens or guaranteed frozen snapshots
+across requests. Concurrent corpus edits may alter later pages.
+
+Only pageSize+1 positions are selected; the extra position indicates more data,
+then full rows and batched metadata are loaded for at most pageSize papers.
+For recent order with only a topic filter, page directly through the existing
+`(tag_id,paper_id)` index and deduplicate evidence before LIMIT. For text/author
+search in recent order, try an ID interval of 512 near the cursor, expanding
+once to 4096 only if there are some matches but fewer than pageSize+1.
+Only a full page plus one proves that interval contains the next page. If neither bounded attempt fills the page,
+all local candidates are discarded and the complete indexed search is used;
+rare or older matches are never silently truncated. The fallback materializes
+matching IDs before sorting, avoiding an unbounded ordered heap scan for sparse
+terms. Title-order filtered queries still use that complete search and can time
+out for broad terms. No global database or proxy resource settings are changed.
+The
 HTTP layer permits two in-flight queries with an eight-second context budget.
 Busy requests return 429 with `Retry-After: 1`; deadlines return 504; storage
 errors return a generic 503 without database details. Missing papers return 404.
@@ -95,7 +114,7 @@ and homepage HTTP routes have returned 200.
 The frontend has also rendered the actual 3,526,999-paper corpus through a
 loopback SSH tunnel: eight rows, matching detail title/source, desktop and
 mobile layout, no page exceptions or horizontal overflow in that check.
-Author search returned 146 records in 0.336 seconds. After paging/author fixes, category `cs.AR` returned 9,457 records in 4.906
+The earlier count-based API returned 146 author records in 0.336 seconds. Before the cursor optimization, after paging/author fixes, category `cs.AR` returned 9,457 records in 4.906
 seconds, `CartoonGAN` returned three in 0.332 seconds, and the multi-term search
 `attention is all you need` returned 8,653 in 6.325 seconds. These were sequential
 manual HTTP checks, not a load test. Very broad text searches can still exceed
@@ -143,3 +162,35 @@ reload/new-tab persistence and logout behavior. Browser control was unavailable,
 so these browser results are attributed to user acceptance rather than an
 automated real-account test. This does not deploy the research work branch;
 mail delivery was not exercised.
+
+
+## Cursor regression coverage
+
+The disposable PostgreSQL fixture covers forward/backward traversal, identical
+title keys with different IDs, published control-character encoding, sparse
+matches separated by a large ID gap, and fallback from the bounded interval.
+Invalid, oversized, cross-filter and wrong-version cursors are rejected before
+repository execution. The runtime reader retains SELECT-only privileges; no DDL
+or writes are added. Run tests manually on the confirmed ECS; skip CI for this
+iteration and retain `[skip ci]` in commit and PR titles.
+
+
+## Manual cursor measurements (2026-11-07)
+
+On the confirmed ECS, after this task's compilation and disposable fixture had
+finished, sequential direct requests to the temporary Core returned: homepage
+65 ms, next/previous 39/21 ms, `graph` 345 ms, `CartoonGAN` 731 ms (3 papers),
+`cs.AR` 145 ms, title order 180 ms, author `Buhrman` 769 ms, and
+`attention is all you need` 1312 ms. Recent, topic and title cursor round trips
+returned the same first page without overlap. These are individual manual
+samples, not production latency guarantees; concurrent compilation earlier
+produced multi-second cold measurements. No proxy, database memory, CPU or
+production configuration was changed.
+
+The final source compiled manually on the ECS; package unit checks and all ten
+selected cursor/PostgreSQL integration tests passed, including interval expansion
+and complete fallback. No CI or local build ran. The local authorized Next dev
+uses the temporary API through the existing SSH tunnel. Independent Chrome also
+verified real homepage/search navigation, a preserved document, one mobile
+header/main, no page exceptions and no horizontal overflow. The production Core
+was not replaced by these temporary preview updates.

internal/platform/assets.go

@@ -65,6 +65,18 @@ func (s *service) uploadAsset(w http.ResponseWriter, r *http.Request, project, a
 		reject(w, 400, "invalid_idempotency_key")
 		return nil
 	}
+	resourceID := strings.ToLower(r.Header.Get("X-Resource-Id"))
+	if resourceID != "" && !uuidSlugPattern.MatchString(resourceID) {
+		reject(w, 400, "invalid_resource_id")
+		return nil
+	}
+	respond := func(info assetInfo) {
+		if resourceID == "" {
+			reply(w, 201, info)
+		} else {
+			reply(w, 201, response{"protocol_version": 2, "request_id": key, "status": "applied", "asset": info})
+		}
+	}
 	tx, err := s.db.BeginTx(r.Context(), nil)
 	if err != nil {
 		return err
@@ -146,18 +158,28 @@ func (s *service) uploadAsset(w http.ResponseWriter, r *http.Request, project, a
 	var previous string
 	err = tx.QueryRowContext(r.Context(), `SELECT id::text,digest FROM canvas_assets WHERE project=$1 AND workspace_id=$2 AND uploaded_by=$3 AND idempotency_key=$4`, project, workspace, account, key).Scan(&info.ID, &previous)
 	if err == nil {
-		if previous != hash {
+		if previous != hash || resourceID != "" && resourceID != info.ID {
 			reject(w, 409, "idempotency_conflict")
 			return nil
 		}
 		info.URL = s.assetURL(project, workspace, info.ID)
-		reply(w, 201, info)
+		respond(info)
 		return nil
 	}
 	if err != sql.ErrNoRows {
 		return err
 	}
-	err = tx.QueryRowContext(r.Context(), `INSERT INTO canvas_assets(project,workspace_id,uploaded_by,mime_type,bytes,width,height,digest,idempotency_key) VALUES($1,$2,$3,$4,$5,$6,$7,$8,$9) RETURNING id::text`, project, workspace, account, mime, encoded, width, height, hash, key).Scan(&info.ID)
+	if resourceID != "" {
+		var occupied bool
+		if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_assets WHERE project=$1 AND workspace_id=$2 AND id=$3)`, project, workspace, resourceID).Scan(&occupied); err != nil {
+			return err
+		}
+		if occupied {
+			reject(w, 409, "resource_identity_conflict")
+			return nil
+		}
+	}
+	err = tx.QueryRowContext(r.Context(), `INSERT INTO canvas_assets(project,workspace_id,uploaded_by,mime_type,bytes,width,height,digest,idempotency_key,id) VALUES($1,$2,$3,$4,$5,$6,$7,$8,$9,COALESCE(NULLIF($10,'')::uuid,gen_random_uuid())) RETURNING id::text`, project, workspace, account, mime, encoded, width, height, hash, key, resourceID).Scan(&info.ID)
 	if err != nil {
 		return err
 	}
@@ -165,7 +187,40 @@ func (s *service) uploadAsset(w http.ResponseWriter, r *http.Request, project, a
 		return err
 	}
 	info.URL = s.assetURL(project, workspace, info.ID)
-	reply(w, 201, info)
+	respond(info)
+	return nil
+}
+
+// A missing receipt is unknown: callers may only retry the same resource/key/bytes.
+func (s *service) assetOperation(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	key, workspace := r.PathValue("request"), r.PathValue("workspace")
+	if !uuidSlugPattern.MatchString(key) {
+		reject(w, 400, "invalid_idempotency_key")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	if _, _, err = lockWorkspace(r.Context(), tx, project, workspace, account); err != nil {
+		return err
+	}
+	var info assetInfo
+	err = tx.QueryRowContext(r.Context(), `SELECT id::text,mime_type,octet_length(bytes),width,height FROM canvas_assets WHERE project=$1 AND workspace_id=$2 AND uploaded_by=$3 AND idempotency_key=$4`, project, workspace, account, key).Scan(&info.ID, &info.MIME, &info.Bytes, &info.Width, &info.Height)
+	if err == sql.ErrNoRows {
+		reply(w, 404, response{"protocol_version": 2, "request_id": key, "status": "unknown", "error": "asset_receipt_unknown"})
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	info.URL = s.assetURL(project, workspace, info.ID)
+	reply(w, 200, response{"protocol_version": 2, "request_id": key, "status": "applied", "asset": info})
 	return nil
 }
 func assetReadable(r *http.Request, tx *sql.Tx, project, workspace, id, account string) (bool, error) {
@@ -216,6 +271,53 @@ func assetReadable(r *http.Request, tx *sql.Tx, project, workspace, id, account
 	}
 	return false, nil
 }
+
+// Metadata uses the same read policy as original bytes; it is not a persistent grant.
+func (s *service) getAssetMetadata(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	id, workspace := r.PathValue("asset"), r.PathValue("workspace")
+	if !uuidSlugPattern.MatchString(id) {
+		reject(w, 404, "not_found")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	var locked string
+	err = tx.QueryRowContext(r.Context(), `SELECT id::text FROM workspaces WHERE project=$1 AND id=$2 FOR UPDATE`, project, workspace).Scan(&locked)
+	if err != nil {
+		return err
+	}
+	allowed, err := assetReadable(r, tx, project, workspace, id, account)
+	if err != nil {
+		return err
+	}
+	if !allowed {
+		reject(w, 404, "not_found")
+		return nil
+	}
+	var info assetInfo
+	var digest string
+	err = tx.QueryRowContext(r.Context(), `SELECT id::text,mime_type,octet_length(bytes),width,height,digest FROM canvas_assets WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, id).Scan(&info.ID, &info.MIME, &info.Bytes, &info.Width, &info.Height, &digest)
+	if err != nil {
+		return err
+	}
+	if err = tx.Commit(); err != nil {
+		return err
+	}
+	info.URL = s.assetURL(project, workspace, id)
+	w.Header().Set("Cache-Control", "private, no-store")
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	_ = json.NewEncoder(w).Encode(response{"metadata_version": 1, "asset": info, "sha256": digest})
+	return nil
+}
+
 func (s *service) getAsset(w http.ResponseWriter, r *http.Request, project, account string) error {
 	if r.Method != http.MethodGet {
 		reject(w, 405, "method_not_allowed")

internal/platform/canvas_ai_apply.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"encoding/json"
+	"errors"
 	"gitea.entroia.com/Zayden-Jung/foundry-core/internal/codex"
 )
 
@@ -13,7 +14,19 @@ func (s *service) startCanvasStep(ctx context.Context, run canvasQueueRun, step
 		return false, err
 	}
 	defer tx.Rollback()
-	_, role, permissionErr := lockMaterial(ctx, tx, run.Project, run.Workspace, step.BoardID, run.Account)
+	if err = lockCanvasAIWorkspace(ctx, tx, run.Project, run.Workspace); err != nil {
+		return false, err
+	}
+	board, identityOK, err := resolveCanvasAITarget(ctx, tx, run.Project, run.Workspace, step)
+	if err != nil {
+		return false, err
+	}
+	if !identityOK {
+		tx.Rollback()
+		_, err = s.finishCanvasStep(ctx, run, step, "", "target_removed", false)
+		return false, err
+	}
+	_, role, permissionErr := lockMaterial(ctx, tx, run.Project, run.Workspace, board, run.Account)
 	if permissionErr != nil || role == "viewer" {
 		tx.Rollback()
 		if permissionErr != nil && permissionErr != sql.ErrNoRows {
@@ -32,12 +45,12 @@ func (s *service) startCanvasStep(ctx context.Context, run canvasQueueRun, step
 		_, err = s.finishCanvasStep(ctx, run, step, "", "generation_cancelled", false)
 		return false, err
 	}
-	snapshot, err := loadCanvas(queueRequest(ctx), tx, run.Project, run.Workspace, step.BoardID)
+	snapshot, err := loadCanvas(queueRequest(ctx), tx, run.Project, run.Workspace, board)
 	if err != nil {
 		return false, err
 	}
 	data := canvasNodeData(snapshot.Document)[step.NodeID]
-	if data == nil || canvasTargetFingerprint(step.BoardID, step.NodeID, data) != step.Fingerprint {
+	if !identityOK || data == nil || canvasTargetFingerprint(step.BoardID, step.NodeID, data) != step.Fingerprint {
 		tx.Rollback()
 		_, err = s.finishCanvasStep(ctx, run, step, "", "target_changed", false)
 		return false, err
@@ -103,7 +116,7 @@ func (s *service) finishCanvasStepOutput(ctx context.Context, run canvasQueueRun
 		status = "skipped"
 	case "target_changed":
 		status = "conflict"
-	case "generation_cancelled":
+	case "generation_cancelled", "target_removed":
 		status = "cancelled"
 	default:
 		if code != "" {
@@ -114,6 +127,16 @@ func (s *service) finishCanvasStepOutput(ctx context.Context, run canvasQueueRun
 		status = "cancelled"
 		code = "generation_cancelled"
 	}
+	board, identityOK, err := resolveCanvasAITarget(ctx, tx, run.Project, run.Workspace, step)
+	if err != nil {
+		return "", err
+	}
+	eventBoard := board
+	if !identityOK {
+		eventBoard = step.BoardID
+	}
+	var appliedBoard any
+	var appliedEvent response
 	var output any
 	var version any
 	if code == "" && started {
@@ -136,10 +159,7 @@ func (s *service) finishCanvasStepOutput(ctx context.Context, run canvasQueueRun
 			patch["text"] = generated.Text
 		}
 
-		if err = appendAIEvent(ctx, tx, run.Project, run.Workspace, run.ID, "step.output", response{"step_id": step.ID, "board_id": step.BoardID, "node_id": step.NodeID, "output": output}); err != nil {
-			return "", err
-		}
-		_, role, permissionErr := lockMaterial(ctx, tx, run.Project, run.Workspace, step.BoardID, run.Account)
+		_, role, permissionErr := lockCanvasAIRunRoute(ctx, tx, run.Project, run.Workspace, eventBoard, run.Account)
 		if permissionErr != nil && permissionErr != sql.ErrNoRows {
 			return "", permissionErr
 		}
@@ -147,53 +167,62 @@ func (s *service) finishCanvasStepOutput(ctx context.Context, run canvasQueueRun
 			status = "failed"
 			code = "permission_revoked"
 		} else {
-			snapshot, err := loadCanvas(queueRequest(ctx), tx, run.Project, run.Workspace, step.BoardID)
+			snapshot, err := loadCanvas(queueRequest(ctx), tx, run.Project, run.Workspace, eventBoard)
 			if err != nil {
 				return "", err
 			}
-			var doc map[string]any
-			if err = json.Unmarshal(snapshot.Document, &doc); err != nil {
-				return "", err
-			}
-			var target map[string]any
-			for _, v := range doc["nodes"].([]any) {
-				n := v.(map[string]any)
-				if n["id"] == step.NodeID {
-					target = n["data"].(map[string]any)
+			target := canvasNodeData(snapshot.Document)[step.NodeID]
+			if image, ok := output.(response); ok && image["kind"] == "image" && identityOK {
+				if _, err = tx.ExecContext(ctx, `INSERT INTO canvas_asset_bindings(project,workspace_id,asset_id,board_id) VALUES($1,$2,$3,$4) ON CONFLICT DO NOTHING`, run.Project, run.Workspace, image["assetId"], eventBoard); err != nil {
+					return "", err
 				}
 			}
-			if target == nil || canvasTargetFingerprint(step.BoardID, step.NodeID, target) != step.Fingerprint {
-				status = "conflict"
-				code = "target_changed"
+			if !identityOK || target == nil || canvasTargetFingerprint(step.BoardID, step.NodeID, target) != step.Fingerprint {
+				status, code = "conflict", "target_changed"
 			} else {
-				for key, value := range patch {
-					target[key] = value
-				}
-				encoded, _ := json.Marshal(doc)
-				normalized, ok := normalizeCanvas(encoded)
-				if !ok {
-					status = "failed"
-					code = "generation_output_too_large"
+				change, err := prepareCanvasAIPatch(queueRequest(ctx), tx, run.Project, run.Workspace, snapshot, step.NodeID, patch)
+				if err != nil {
+					if !errors.Is(err, errAIInvalidPatch) && !errors.Is(err, errCanvasModel) && !errors.Is(err, errGraphCapacity) {
+						return "", err
+					}
+					status, code = "failed", "generation_output_too_large"
 				} else {
-					snapshot.Document = normalized
-					snapshot.Version++
-					if err = s.saveCanvas(queueRequest(ctx), tx, run.Project, run.Workspace, snapshot); err != nil {
-						return "", err
-					}
-					version = snapshot.Version
-					if err = appendAIEvent(ctx, tx, run.Project, run.Workspace, run.ID, "step.applied", response{"step_id": step.ID, "board_id": step.BoardID, "node_id": step.NodeID, "patch": patch, "canvas_version": snapshot.Version}); err != nil {
+					if err = s.saveCanvasAIChange(queueRequest(ctx), tx, run.Project, run.Workspace, run.Account, change); err != nil {
 						return "", err
 					}
+					version = change.Snapshot.Version
+					appliedBoard = eventBoard
+					applied := response{"step_id": step.ID, "board_id": eventBoard, "node_id": step.NodeID, "patch": patch, "canvas_version": change.Snapshot.Version}
+					change.addTargetContext(applied, step)
+					appliedEvent = applied
 				}
 			}
 		}
 	}
+	if output != nil {
+		event := response{"step_id": step.ID, "board_id": eventBoard, "origin_board_id": step.BoardID, "canonical_root": step.CanonicalRoot, "target_incarnation": step.TargetIncarnation, "node_id": step.NodeID, "output": output}
+		if status == "conflict" && identityOK && step.CanonicalRoot != "" && eventBoard != step.BoardID {
+			model, e := loadCanvasModel(ctx, tx, run.Project, run.Workspace, step.CanonicalRoot)
+			if e != nil {
+				return "", e
+			}
+			event["model"], event["document_format_version"], event["canvas_version"] = model.view(nil), canvasModelFormat, model.Versions[eventBoard]
+		}
+		if err = appendAIEvent(ctx, tx, run.Project, run.Workspace, run.ID, "step.output", event); err != nil {
+			return "", err
+		}
+	}
+	if appliedEvent != nil {
+		if err = appendAIEvent(ctx, tx, run.Project, run.Workspace, run.ID, "step.applied", appliedEvent); err != nil {
+			return "", err
+		}
+	}
 	var outputJSON any
 	if output != nil {
 		encoded, _ := json.Marshal(output)
 		outputJSON = encoded
 	}
-	_, err = tx.ExecContext(ctx, `UPDATE canvas_ai_steps SET status=$5,output=$6,error_code=NULLIF($7,''),applied_version=$8,completed_at=now() WHERE project=$1 AND workspace_id=$2 AND run_id=$3 AND id=$4`, run.Project, run.Workspace, run.ID, step.ID, status, outputJSON, code, version)
+	_, err = tx.ExecContext(ctx, `UPDATE canvas_ai_steps SET status=$5,output=$6,error_code=NULLIF($7,''),applied_version=$8,applied_board_id=$9,completed_at=now() WHERE project=$1 AND workspace_id=$2 AND run_id=$3 AND id=$4`, run.Project, run.Workspace, run.ID, step.ID, status, outputJSON, code, version, appliedBoard)
 	if err != nil {
 		return "", err
 	}

internal/platform/canvas_ai_cancel.go

@@ -22,29 +22,70 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		reject(w, 413, "context_too_large")
 		return nil
 	}
-	input := map[string]any{}
-	if len(raw) > 0 && (json.Unmarshal(raw, &input) != nil || input == nil || len(input) > 0) {
+	var input struct {
+		ProtocolVersion int    `json:"protocol_version,omitempty"`
+		RequestID       string `json:"request_id,omitempty"`
+		OperationID     string `json:"operation_id,omitempty"`
+	}
+	if len(raw) > 0 && (json.Unmarshal(raw, &input) != nil || string(raw) == "null") {
 		reject(w, 400, "invalid_ai_request")
 		return nil
 	}
-	hash := payloadDigest(input)
+	var fields map[string]any
+	if len(raw) > 0 {
+		if json.Unmarshal(raw, &fields) != nil || fields == nil {
+			reject(w, 400, "invalid_ai_request")
+			return nil
+		}
+		for key := range fields {
+			if key != "protocol_version" && key != "request_id" && key != "operation_id" {
+				reject(w, 400, "invalid_ai_request")
+				return nil
+			}
+		}
+	}
+	canonical := input.ProtocolVersion != 0 || input.RequestID != "" || input.OperationID != ""
+	if canonical && (input.ProtocolVersion != 2 || input.RequestID != key || !uuidSlugPattern.MatchString(input.OperationID) || !acceptsCanvasV2(r)) {
+		reject(w, 400, "invalid_ai_protocol")
+		return nil
+	}
+	if !canonical && len(fields) > 0 {
+		reject(w, 400, "invalid_ai_request")
+		return nil
+	}
+	hash := payloadDigest(map[string]any{})
+	if canonical {
+		hash = payloadDigest(input)
+	}
 	workspace, board := r.PathValue("workspace"), r.PathValue("material")
 	tx, err := s.db.BeginTx(r.Context(), nil)
 	if err != nil {
 		return err
 	}
 	defer tx.Rollback()
-	_, role, err := lockMaterial(r.Context(), tx, project, workspace, board, account)
+	_, role, err := lockCanvasAIRunRoute(r.Context(), tx, project, workspace, board, account)
 	if err != nil {
 		return err
 	}
+	var receipt *canvasAIRequest
+	if canonical {
+		receipt = &canvasAIRequest{Key: key, Hash: hash, Action: "run.cancel", Board: board, Run: id, Operation: input.OperationID}
+		if done, e := beginCanvasAIRequest(w, r, tx, project, workspace, account, receipt); done || e != nil {
+			return e
+		}
+	}
+	rejectRequest := func(status int, code string) error {
+		return rejectCanvasAIRequest(w, r, tx, project, workspace, account, receipt, status, code)
+	}
 	if role == "viewer" {
-		reject(w, 403, "forbidden")
-		return nil
+		return rejectRequest(403, "forbidden")
 	}
 	var status string
 	var rawPlan json.RawMessage
 	err = tx.QueryRowContext(r.Context(), `SELECT status,plan FROM canvas_ai_runs WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND id=$4 FOR UPDATE`, project, workspace, board, id).Scan(&status, &rawPlan)
+	if err == sql.ErrNoRows {
+		return rejectRequest(404, "not_found")
+	}
 	if err != nil {
 		return err
 	}
@@ -67,13 +108,19 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		return err
 	}
 	for _, step := range plan.Steps {
-		_, role, err := lockMaterial(r.Context(), tx, project, workspace, step.BoardID, account)
+		target, ok, e := resolveCanvasAITarget(r.Context(), tx, project, workspace, step)
+		if e != nil {
+			return e
+		}
+		if !ok {
+			target = step.BoardID
+		}
+		_, role, err := lockCanvasAIRunRoute(r.Context(), tx, project, workspace, target, account)
 		if err != nil {
 			return err
 		}
 		if role == "viewer" {
-			reject(w, 403, "forbidden")
-			return nil
+			return rejectRequest(403, "forbidden")
 		}
 	}
 	if status == "queued" || status == "running" {
@@ -119,7 +166,7 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			return err
 		}
 	}
-	rows, err := tx.QueryContext(r.Context(), `SELECT id,board_id::text,node_id,status,applied_version FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND run_id=$3 ORDER BY ordinal`, project, workspace, id)
+	rows, err := tx.QueryContext(r.Context(), `SELECT id,COALESCE(applied_board_id,board_id)::text,node_id,status,applied_version FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND run_id=$3 ORDER BY ordinal`, project, workspace, id)
 	if err != nil {
 		return err
 	}
@@ -145,14 +192,14 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		return err
 	}
 	result := response{"run_id": id, "status": status, "applied": applied, "cancelled_step_ids": cancelledSteps, "worker_stop_grace_ms": 1000}
+	if receipt != nil {
+		result["run_status"], result["status"] = status, "applied"
+		bindCanvasAIReceipt(result, receipt)
+	}
 	encoded, _ := json.Marshal(result)
 	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_ai_mutations(project,workspace_id,run_id,account_id,action,idempotency_key,payload_hash,response_body) VALUES($1,$2,$3,$4,'cancel',$5,$6,$7)`, project, workspace, id, account, key, hash, encoded)
 	if err != nil {
 		return err
 	}
-	if err = tx.Commit(); err != nil {
-		return err
-	}
-	reply(w, 200, result)
-	return nil
+	return commitCanvasAIReceipt(w, r, tx, project, workspace, account, receipt, 200, "applied", result)
 }

internal/platform/canvas_ai_config.go

@@ -43,7 +43,9 @@ func validCanvasAI(value any, kind string) bool {
 }
 
 // Fingerprints exclude geometry and visual styles so a result can be applied
-// after a concurrent drag. Content/configuration edits invalidate the result.
+// after a concurrent drag. The board is the immutable plan origin, not the
+// current canonical owner; canonical target identity is checked separately.
+// Content/configuration edits invalidate the result.
 func canvasTargetFingerprint(board, node string, data map[string]any) string {
 	target := map[string]any{"board_id": board, "node_id": node, "kind": data["kind"], "ai": data["ai"]}
 	if canvasChoice(data["kind"], "image", "plain-image") {

internal/platform/canvas_ai_explicit_apply.go

@@ -22,8 +22,13 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 		return nil
 	}
 	var input struct {
-		NodeID   string `json:"node_id"`
-		OutputID string `json:"output_id"`
+		ProtocolVersion   int    `json:"protocol_version,omitempty"`
+		RequestID         string `json:"request_id,omitempty"`
+		OperationID       string `json:"operation_id,omitempty"`
+		TargetIncarnation int64  `json:"target_incarnation,omitempty"`
+		TargetCanvasID    string `json:"target_canvas_id,omitempty"`
+		NodeID            string `json:"node_id"`
+		OutputID          string `json:"output_id"`
 	}
 	if !decode(w, r, &input) {
 		return nil
@@ -32,23 +37,43 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 		reject(w, 400, "invalid_ai_request")
 		return nil
 	}
+	canonical := input.ProtocolVersion != 0 || input.RequestID != "" || input.OperationID != "" || input.TargetIncarnation != 0 || input.TargetCanvasID != ""
+	if canonical && (input.ProtocolVersion != 2 || input.RequestID != key || !uuidSlugPattern.MatchString(input.OperationID) || input.TargetIncarnation < 1 || !uuidSlugPattern.MatchString(input.TargetCanvasID) || !acceptsCanvasV2(r)) {
+		reject(w, 400, "invalid_ai_protocol")
+		return nil
+	}
 	hash := payloadDigest(input)
+	if canonical {
+		hash = payloadDigest(response{"input": input, "if_match": expected})
+	}
 	workspace, board := r.PathValue("workspace"), r.PathValue("material")
 	tx, err := s.db.BeginTx(r.Context(), nil)
 	if err != nil {
 		return err
 	}
 	defer tx.Rollback()
-	_, role, err := lockMaterial(r.Context(), tx, project, workspace, board, account)
+	_, role, err := lockCanvasAIRunRoute(r.Context(), tx, project, workspace, board, account)
 	if err != nil {
 		return err
 	}
+	var receipt *canvasAIRequest
+	if canonical {
+		receipt = &canvasAIRequest{Key: key, Hash: hash, Action: "run.apply", Board: board, Run: id, Operation: input.OperationID}
+		if done, e := beginCanvasAIRequest(w, r, tx, project, workspace, account, receipt); done || e != nil {
+			return e
+		}
+	}
+	rejectRequest := func(status int, code string) error {
+		return rejectCanvasAIRequest(w, r, tx, project, workspace, account, receipt, status, code)
+	}
 	if role == "viewer" {
-		reject(w, 403, "forbidden")
-		return nil
+		return rejectRequest(403, "forbidden")
 	}
 	var runStatus string
 	err = tx.QueryRowContext(r.Context(), `SELECT status FROM canvas_ai_runs WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND id=$4 FOR UPDATE`, project, workspace, board, id).Scan(&runStatus)
+	if err == sql.ErrNoRows {
+		return rejectRequest(404, "not_found")
+	}
 	if err != nil {
 		return err
 	}
@@ -75,28 +100,14 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 	var outputRaw, frozenRaw json.RawMessage
 	var applied sql.NullInt64
 	err = tx.QueryRowContext(r.Context(), `SELECT id,board_id::text,node_id,status,output,frozen_input,applied_version FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND run_id=$3 AND output->>'output_id'=$4 FOR UPDATE`, project, workspace, id, input.OutputID).Scan(&stepID, &targetBoard, &node, &status, &outputRaw, &frozenRaw, &applied)
+	if err == sql.ErrNoRows {
+		return rejectRequest(404, "not_found")
+	}
 	if err != nil {
 		return err
 	}
 	if node != input.NodeID || status != "conflict" || applied.Valid || runStatus == "cancelled" {
-		reject(w, 409, "output_not_applicable")
-		return nil
-	}
-	_, role, err = lockMaterial(r.Context(), tx, project, workspace, targetBoard, account)
-	if err != nil {
-		return err
-	}
-	if role == "viewer" {
-		reject(w, 403, "forbidden")
-		return nil
-	}
-	snapshot, err := loadCanvas(r, tx, project, workspace, targetBoard)
-	if err != nil {
-		return err
-	}
-	if snapshot.Version != expected {
-		reject(w, 412, "version_conflict")
-		return nil
+		return rejectRequest(409, "output_not_applicable")
 	}
 	var output struct {
 		Kind    string `json:"kind"`
@@ -111,32 +122,55 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 	if err = json.Unmarshal(frozenRaw, &frozen); err != nil {
 		return err
 	}
+	if canonical && (frozen.TargetIncarnation != input.TargetIncarnation || frozen.CanonicalRoot == "") {
+		return rejectRequest(409, "target_changed")
+	}
+	targetBoard, identityOK, err := resolveCanvasAITarget(r.Context(), tx, project, workspace, frozen)
+	if err != nil {
+		return err
+	}
+	if !identityOK {
+		return rejectRequest(409, "target_changed")
+	}
+	if canonical && targetBoard != input.TargetCanvasID {
+		return rejectRequest(409, "target_changed")
+	}
+	_, role, err = lockMaterial(r.Context(), tx, project, workspace, targetBoard, account)
+	if err != nil {
+		return err
+	}
+	if role == "viewer" {
+		return rejectRequest(403, "forbidden")
+	}
+	snapshot, err := loadCanvas(r, tx, project, workspace, targetBoard)
+	if err != nil {
+		return err
+	}
+	if snapshot.Version != expected {
+		return rejectRequest(412, "version_conflict")
+	}
 	patch := response{}
 	switch output.Kind {
 	case "text":
 		if !canvasChoice(frozen.Kind, "text", "script", "plain-text") || !utf8.ValidString(output.Text) || utf8.RuneCountInString(output.Text) > 100000 {
-			reject(w, 422, "model_incompatible")
-			return nil
+			return rejectRequest(422, "model_incompatible")
 		}
 		patch["text"] = output.Text
 	case "image":
 		if !canvasChoice(frozen.Kind, "image", "plain-image") || !uuidSlugPattern.MatchString(output.AssetID) || output.Src != s.assetURL(project, workspace, output.AssetID) {
-			reject(w, 422, "model_incompatible")
-			return nil
+			return rejectRequest(422, "model_incompatible")
 		}
 		readable, err := assetReadable(r, tx, project, workspace, output.AssetID, account)
 		if err != nil {
 			return err
 		}
 		if !readable {
-			reject(w, 404, "not_found")
-			return nil
+			return rejectRequest(404, "not_found")
 		}
 		patch["src"] = output.Src
 		patch["assetId"] = output.AssetID
 	default:
-		reject(w, 422, "model_incompatible")
-		return nil
+		return rejectRequest(422, "model_incompatible")
 	}
 
 	var doc map[string]any
@@ -151,44 +185,38 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 		}
 	}
 	if target == nil {
-		reject(w, 404, "not_found")
-		return nil
+		return rejectRequest(404, "not_found")
 	}
 	if target["kind"] != frozen.Kind {
-		reject(w, 409, "ownership_conflict")
-		return nil
+		return rejectRequest(409, "ownership_conflict")
 	}
-	for key, value := range patch {
-		target[key] = value
+	change, err := prepareCanvasAIPatch(r, tx, project, workspace, snapshot, node, patch)
+	if err != nil {
+		return rejectRequest(413, "canvas_too_large")
 	}
-	encoded, _ := json.Marshal(doc)
-	normalized, ok := normalizeCanvas(encoded)
-	if !ok {
-		reject(w, 413, "canvas_too_large")
-		return nil
-	}
-	snapshot.Document = normalized
-	snapshot.Version++
-	if err = s.saveCanvas(r, tx, project, workspace, snapshot); err != nil {
+	snapshot = change.Snapshot
+	if err = s.saveCanvasAIChange(r, tx, project, workspace, account, change); err != nil {
 		return err
 	}
-	_, err = tx.ExecContext(r.Context(), `UPDATE canvas_ai_steps SET applied_version=$5 WHERE project=$1 AND workspace_id=$2 AND run_id=$3 AND id=$4`, project, workspace, id, stepID, snapshot.Version)
+
+	_, err = tx.ExecContext(r.Context(), `UPDATE canvas_ai_steps SET applied_version=$5,applied_board_id=$6 WHERE project=$1 AND workspace_id=$2 AND run_id=$3 AND id=$4`, project, workspace, id, stepID, snapshot.Version, targetBoard)
 	if err != nil {
 		return err
 	}
 	result := response{"run_id": id, "step_id": stepID, "board_id": targetBoard, "node_id": node, "output_id": input.OutputID, "canvas_version": snapshot.Version, "patch": patch}
+	change.addTargetContext(result, frozen)
+	if receipt != nil {
+		result["status"] = "applied"
+		bindCanvasAIReceipt(result, receipt)
+	}
 	if err = appendAIEvent(r.Context(), tx, project, workspace, id, "step.applied", result); err != nil {
 		return err
 	}
-	encoded, _ = json.Marshal(result)
+	encoded, _ := json.Marshal(result)
 	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_ai_mutations(project,workspace_id,run_id,account_id,action,idempotency_key,payload_hash,response_body) VALUES($1,$2,$3,$4,'apply',$5,$6,$7)`, project, workspace, id, account, key, hash, encoded)
 	if err != nil {
 		return err
 	}
-	if err = tx.Commit(); err != nil {
-		return err
-	}
 	setVersion(w, snapshot.Version)
-	reply(w, 200, result)
-	return nil
+	return commitCanvasAIReceipt(w, r, tx, project, workspace, account, receipt, 200, "applied", result)
 }

internal/platform/canvas_ai_image_inputs.go

@@ -166,7 +166,17 @@ func (s *service) hydrateCanvasTask(ctx context.Context, run canvasQueueRun, ste
 		return err
 	}
 	defer tx.Rollback()
-	_, role, err := lockMaterial(ctx, tx, run.Project, run.Workspace, step.BoardID, run.Account)
+	if err = lockCanvasAIWorkspace(ctx, tx, run.Project, run.Workspace); err != nil {
+		return err
+	}
+	board, ok, err := resolveCanvasAITarget(ctx, tx, run.Project, run.Workspace, step)
+	if err != nil {
+		return err
+	}
+	if !ok {
+		return errors.New("target_removed")
+	}
+	_, role, err := lockMaterial(ctx, tx, run.Project, run.Workspace, board, run.Account)
 	if err != nil {
 		return err
 	}

internal/platform/canvas_ai_model.go

@@ -0,0 +1,267 @@
+package platform
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"errors"
+	"net/http"
+)
+
+var errAITargetChanged = errors.New("target_changed")
+var errAIInvalidPatch = errors.New("invalid_ai_patch")
+
+// The snapshot is an AI reader projection only. Canonical changes retain the
+// original rows, including unknown envelopes, geometry and reference metadata.
+type canvasAIChange struct {
+	Snapshot    canvasSnapshot
+	Before      *canvasModel
+	After       *canvasModel
+	Incarnation int64
+}
+
+// Until a narrower read-set protocol exists, admission binds every active
+// canvas in this canonical project. Archived versions are not graph inputs.
+// Workspace locking keeps validation, plan freezing and admission atomic.
+func validateCanvasAIVersions(model canvasModel, board string, header int64, expected map[string]int64) string {
+	if len(expected) != len(model.Canvases) || expected[board] != header {
+		return "invalid_ai_versions"
+	}
+	for id := range model.Canvases {
+		version, ok := expected[id]
+		if !ok || version < 1 || version > 9007199254740991 {
+			return "invalid_ai_versions"
+		}
+		if version != model.Versions[id] {
+			return "version_conflict"
+		}
+	}
+	return ""
+}
+
+func prepareModelAIPatch(before canvasModel, board, node string, patch response) (canvasModel, error) {
+	element := before.Elements[node]
+	if element == nil || element["structure"] != "node" || element["ownerCanvasId"] != board || modelInt(element["dataVersion"]) != 1 || !canvasChoice(element["componentId"], "text", "script", "plain-text", "image", "plain-image") {
+		return canvasModel{}, errAITargetChanged
+	}
+	after := cloneModel(before)
+	data := after.Elements[node]["data"].(map[string]any)
+	for key, value := range patch {
+		if !canvasChoice(key, "ai", "text", "src", "assetId") {
+			return canvasModel{}, errAIInvalidPatch
+		}
+		data[key] = value
+	}
+	if before.Versions[board] < 1 || before.Versions[board] >= 9007199254740991 {
+		return canvasModel{}, errModelConflict
+	}
+	after.Versions[board]++
+	if err := validateCanvasModel(after); err != nil {
+		return canvasModel{}, err
+	}
+	return after, nil
+}
+func prepareCanvasAIPatch(r *http.Request, tx *sql.Tx, project, workspace string, snapshot canvasSnapshot, node string, patch response) (canvasAIChange, error) {
+	change := canvasAIChange{Snapshot: snapshot}
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, snapshot.BoardID)
+	if err != nil {
+		return change, err
+	}
+	if root != "" {
+		before, err := loadCanvasModel(r.Context(), tx, project, workspace, root)
+		if err != nil {
+			return change, err
+		}
+		if before.Versions[snapshot.BoardID] != snapshot.Version {
+			return change, errModelConflict
+		}
+		after, err := prepareModelAIPatch(before, snapshot.BoardID, node, patch)
+		if err != nil {
+			return change, err
+		}
+		projection, err := projectCanvasModel(after)
+		if err != nil {
+			return change, err
+		}
+		change.Before, change.After = &before, &after
+		change.Incarnation = modelInt(before.Elements[node]["incarnation"])
+		change.Snapshot.Document, change.Snapshot.Version = projection[snapshot.BoardID], after.Versions[snapshot.BoardID]
+		return change, nil
+	}
+	var document map[string]any
+	if err = json.Unmarshal(snapshot.Document, &document); err != nil {
+		return change, err
+	}
+	target := canvasNodeData(snapshot.Document)[node]
+	if target == nil {
+		return change, errAITargetChanged
+	}
+	// The data lookup owns a separate decode. Update the staged document itself.
+	for _, raw := range document["nodes"].([]any) {
+		element := raw.(map[string]any)
+		if element["id"] != node {
+			continue
+		}
+		data := element["data"].(map[string]any)
+		for key, value := range patch {
+			if !canvasChoice(key, "ai", "text", "src", "assetId") {
+				return change, errAIInvalidPatch
+			}
+			data[key] = value
+		}
+	}
+	document["schema_version"] = float64(2)
+	encoded, err := json.Marshal(document)
+	if err != nil {
+		return change, err
+	}
+	normalized, ok := normalizeCanvas(encoded)
+	if !ok {
+		return change, errAIInvalidPatch
+	}
+	change.Snapshot.Document = normalized
+	change.Snapshot.Version++
+	return change, nil
+}
+func (s *service) saveCanvasAIChange(r *http.Request, tx *sql.Tx, project, workspace, account string, change canvasAIChange) error {
+	if change.After == nil {
+		return s.saveCanvas(r, tx, project, workspace, change.Snapshot)
+	}
+	return s.saveCanvasModel(r, tx, project, workspace, account, *change.Before, *change.After, map[string]bool{change.Snapshot.BoardID: true})
+}
+func (change canvasAIChange) addCanonical(result response) {
+	if change.After == nil {
+		return
+	}
+	board := change.Snapshot.BoardID
+	result["document_format_version"], result["target_incarnation"] = canvasModelFormat, change.Incarnation
+	result["model"] = change.After.view(map[string]int64{board: change.Snapshot.Version})
+}
+
+func canvasAIIdentity(ctx context.Context, tx *sql.Tx, project, workspace, board, node string) (string, int64, string, error) {
+	root, err := canonicalRoot(ctx, tx, project, workspace, board)
+	if err != nil || root == "" {
+		return root, 0, "", err
+	}
+	var incarnation, version int64
+	var kind string
+	err = tx.QueryRowContext(ctx, `SELECT incarnation,record->>'componentId',(record->>'dataVersion')::bigint FROM canvas_model_elements WHERE project=$1 AND workspace_id=$2 AND root_id=$3 AND element_id=$4 AND owner_canvas_id=$5 AND NOT deleted AND record->>'structure'='node'`, project, workspace, root, node, board).Scan(&incarnation, &kind, &version)
+	if err == sql.ErrNoRows {
+		return root, 0, "", nil
+	}
+	if err != nil {
+		return root, 0, "", err
+	}
+	if version != 1 || !canvasChoice(kind, "text", "script", "plain-text", "image", "plain-image") {
+		return root, 0, "", nil
+	}
+	return root, incarnation, kind, nil
+}
+func bindCanvasAIIdentities(ctx context.Context, tx *sql.Tx, project, workspace string, plan *canvasAIPlan) error {
+	for i, step := range plan.Steps {
+		root, incarnation, kind, err := canvasAIIdentity(ctx, tx, project, workspace, step.BoardID, step.NodeID)
+		if err != nil {
+			return err
+		}
+		if root != "" && (incarnation < 1 || kind != step.Kind) {
+			return errAITargetChanged
+		}
+		plan.Steps[i].CanonicalRoot, plan.Steps[i].TargetIncarnation = root, incarnation
+	}
+	return nil
+}
+
+// Run URLs remain anchored at their admission board, even after that partition
+// is archived. Canonical ownership grants are inherited from the same root.
+func lockCanvasAIRunRoute(ctx context.Context, tx *sql.Tx, project, workspace, board, account string) (string, string, error) {
+	root, err := canonicalRoot(ctx, tx, project, workspace, board)
+	if err != nil {
+		return "", "", err
+	}
+	if root != "" {
+		board = root
+	}
+	return lockMaterial(ctx, tx, project, workspace, board, account)
+}
+func lockCanvasAIWorkspace(ctx context.Context, tx *sql.Tx, project, workspace string) error {
+	var id string
+	return tx.QueryRowContext(ctx, `SELECT id::text FROM workspaces WHERE project=$1 AND id=$2 FOR UPDATE`, project, workspace).Scan(&id)
+}
+
+// Caller holds the workspace lock. Frozen identity is stable; owner is resolved
+// afresh at execution, hydration and write time, never written into the plan.
+func resolveCanvasAITarget(ctx context.Context, tx *sql.Tx, project, workspace string, step canvasAIStepPlan) (string, bool, error) {
+	if step.CanonicalRoot == "" {
+		root, err := canonicalRoot(ctx, tx, project, workspace, step.BoardID)
+		return step.BoardID, err == nil && root == "" && step.TargetIncarnation == 0, err
+	}
+	var board, kind string
+	var incarnation, version int64
+	err := tx.QueryRowContext(ctx, `SELECT e.owner_canvas_id::text,e.incarnation,e.record->>'componentId',(e.record->>'dataVersion')::bigint FROM canvas_model_elements e JOIN canvas_model_canvases c ON c.project=e.project AND c.workspace_id=e.workspace_id AND c.canvas_id=e.owner_canvas_id AND c.root_id=e.root_id WHERE e.project=$1 AND e.workspace_id=$2 AND e.root_id=$3 AND e.element_id=$4 AND NOT e.deleted AND NOT c.archived AND e.record->>'structure'='node'`, project, workspace, step.CanonicalRoot, step.NodeID).Scan(&board, &incarnation, &kind, &version)
+	if err == sql.ErrNoRows {
+		return "", false, nil
+	}
+	if err != nil {
+		return "", false, err
+	}
+	return board, incarnation == step.TargetIncarnation && incarnation > 0 && kind == step.Kind && version == 1, nil
+}
+func canvasAIIdentityMatches(ctx context.Context, tx *sql.Tx, project, workspace string, step canvasAIStepPlan) (bool, error) {
+	_, ok, err := resolveCanvasAITarget(ctx, tx, project, workspace, step)
+	return ok, err
+}
+func (change canvasAIChange) addTargetContext(result response, step canvasAIStepPlan) {
+	change.addCanonical(result)
+	if step.CanonicalRoot != "" {
+		result["origin_board_id"], result["canonical_root"] = step.BoardID, step.CanonicalRoot
+		if change.After != nil && change.Snapshot.BoardID != step.BoardID {
+			result["model"] = change.After.view(nil)
+		}
+	}
+}
+
+// Whole identity transitions cancel old jobs even when delete/restore happens
+// in a single atomic batch and the compatibility projection looks identical.
+func invalidateCanonicalAIIdentities(r *http.Request, tx *sql.Tx, project, workspace string, before, after canvasModel) error {
+	removed := map[string][]any{}
+	for id, element := range before.Elements {
+		if element["structure"] != "node" {
+			continue
+		}
+		next := after.Elements[id]
+		if next != nil && modelInt(next["incarnation"]) == modelInt(element["incarnation"]) && next["componentId"] == element["componentId"] && modelInt(next["dataVersion"]) == modelInt(element["dataVersion"]) {
+			continue
+		}
+		rows, err := tx.QueryContext(r.Context(), `SELECT DISTINCT board_id::text FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND frozen_input->>'canonical_root'=$3 AND node_id=$4 AND frozen_input->>'target_incarnation'=$5::bigint::text AND status IN('queued','running')`, project, workspace, before.Root, id, modelInt(element["incarnation"]))
+		if err != nil {
+			return err
+		}
+		boards := []string{}
+		for rows.Next() {
+			var board string
+			if err = rows.Scan(&board); err != nil {
+				rows.Close()
+				return err
+			}
+			boards = append(boards, board)
+		}
+		err = rows.Err()
+		rows.Close()
+		if err != nil {
+			return err
+		}
+		for _, board := range boards {
+			removed[board] = append(removed[board], map[string]any{"id": id, "data": map[string]any{"kind": element["componentId"]}})
+		}
+	}
+	for _, board := range sortedKeys(removed) {
+		raw, err := json.Marshal(map[string]any{"nodes": removed[board]})
+		if err != nil {
+			return err
+		}
+		if err = invalidateCanvasAITargets(r, tx, project, workspace, board, raw, json.RawMessage(`{"nodes":[]}`)); err != nil {
+			return err
+		}
+	}
+	return nil
+}

internal/platform/canvas_ai_model_integration_test.go

@@ -0,0 +1,536 @@
+package platform
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"image"
+	"image/png"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync/atomic"
+	"testing"
+
+	"gitea.entroia.com/Zayden-Jung/foundry-core/internal/codex"
+)
+
+func TestCanonicalAIAdmissionAndLifecycle(t *testing.T) {
+	dsn := os.Getenv("PLATFORM_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("requires an isolated integration database")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	ctx := context.Background()
+	var entropy [32]byte
+	_, _ = rand.Read(entropy[:])
+	project := "canonical-ai-" + hex.EncodeToString(entropy[:8])
+	token := base64.RawURLEncoding.EncodeToString(entropy[:])
+	digest := sha256.Sum256([]byte(token))
+	var account, workspace, root string
+	if err = db.QueryRowContext(ctx, `INSERT INTO project_accounts(project,id) VALUES($1,gen_random_uuid()) RETURNING id::text`, project).Scan(&account); err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		for _, table := range []string{"canvas_ai_runs", "canvas_model_operations", "canvas_model_identity_map", "canvas_model_requests", "canvas_model_projects", "canvas_asset_bindings", "canvas_assets", "canvas_subgraphs", "workspaces", "project_accounts"} {
+			_, _ = db.ExecContext(ctx, "DELETE FROM "+table+" WHERE project=$1", project)
+		}
+	}()
+	if _, err = db.ExecContext(ctx, `INSERT INTO project_sessions(token_hash,project,account_id,expires_at) VALUES($1,$2,$3,now()+interval '1 hour')`, base64.RawURLEncoding.EncodeToString(digest[:]), project, account); err != nil {
+		t.Fatal(err)
+	}
+	if err = db.QueryRowContext(ctx, `INSERT INTO workspaces(project,name,owner_id) VALUES($1,'Canonical AI',$2) RETURNING id::text`, project, account).Scan(&workspace); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = db.ExecContext(ctx, `INSERT INTO workspace_members(project,workspace_id,account_id,role) VALUES($1,$2,$3,'admin')`, project, workspace, account); err != nil {
+		t.Fatal(err)
+	}
+	if err = db.QueryRowContext(ctx, `INSERT INTO materials(project,workspace_id,kind,title,created_by,canvas_document) VALUES($1,$2,'board','Canonical AI',$3,$4) RETURNING id::text`, project, workspace, account, json.RawMessage(canvasFixture)).Scan(&root); err != nil {
+		t.Fatal(err)
+	}
+	temp, err := os.MkdirTemp("", "fc-canonical-ai-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(temp)
+	socket := filepath.Join(temp, "worker.sock")
+	listener, err := net.Listen("unix", socket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var pngBytes bytes.Buffer
+	if err = png.Encode(&pngBytes, image.NewRGBA(image.Rect(0, 0, 3, 2))); err != nil {
+		t.Fatal(err)
+	}
+	hooks := make(chan func(), 1)
+	var executions atomic.Int32
+	worker := &http.Server{Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/canvas/models" {
+			reply(w, 200, response{"models": []any{codex.CanvasModel{ID: "text", Available: true, InputModalities: []string{"text", "image"}, OutputModalities: []string{"text"}, MaxInputBytes: 1 << 20, MaxExecutionMS: 90000}, codex.CanvasModel{ID: "image", Available: true, InputModalities: []string{"text", "image"}, OutputModalities: []string{"image"}, MaxInputBytes: 1 << 20, MaxExecutionMS: 180000}}})
+			return
+		}
+		if r.URL.Path != "/canvas/exec" {
+			reject(w, 404, "not_found")
+			return
+		}
+		var task codex.CanvasTask
+		if json.NewDecoder(r.Body).Decode(&task) != nil {
+			reject(w, 400, "invalid_request")
+			return
+		}
+		executions.Add(1)
+		select {
+		case hook := <-hooks:
+			hook()
+		default:
+		}
+		if task.OutputModality == "image" {
+			reply(w, 200, response{"output": codex.CanvasOutput{Kind: "image", Image: &codex.CanvasImage{MIME: "image/png", Data: pngBytes.Bytes()}}})
+		} else {
+			reply(w, 200, response{"result": "generated result"})
+		}
+	})}
+	go worker.Serve(listener)
+	defer worker.Close()
+	s := &service{db: db, origin: "https://api.example.com", canvasAI: codex.NewCanvasClient(socket)}
+	callbacks := map[string]string{project: "https://app.example.com/auth/callback"}
+	mux := http.NewServeMux()
+	prefix := "/projects/{project}/workspaces/{workspace}/materials/{material}/canvas"
+	mux.HandleFunc(prefix+"/model", s.protected(callbacks, s.getCanvasModel))
+	mux.HandleFunc(prefix+"/model/migrate", s.protected(callbacks, s.migrateCanonicalCanvas))
+	mux.HandleFunc(prefix+"/ai/runs", s.protected(callbacks, s.createCanvasAIRun))
+	mux.HandleFunc(prefix+"/ai/runs/{run}", s.protected(callbacks, s.getCanvasAIRun))
+	mux.HandleFunc(prefix+"/ai/runs/{run}/apply", s.protected(callbacks, s.applyCanvasAIOutput))
+	mux.HandleFunc(prefix+"/ai/runs/{run}/cancel", s.protected(callbacks, s.cancelCanvasAIRun))
+	mux.HandleFunc(prefix+"/ai/operations/{request}", s.protected(callbacks, s.getCanvasAIAdmission))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/{asset}", s.protected(callbacks, s.getAsset))
+	base := func(board string) string {
+		return "/projects/" + project + "/workspaces/" + workspace + "/materials/" + board + "/canvas"
+	}
+	call := func(method, path string, input any, status int, version int64, key string) response {
+		t.Helper()
+		raw, _ := json.Marshal(input)
+		r := httptest.NewRequest(method, path, bytes.NewReader(raw))
+		r.Header.Set("Authorization", "Bearer "+token)
+		r.Header.Set("Accept", "application/vnd.foundry.canvas+json;version=2")
+		if version > 0 {
+			r.Header.Set("If-Match", `"`+strconv.FormatInt(version, 10)+`"`)
+		}
+		if key != "" {
+			r.Header.Set("Idempotency-Key", key)
+		}
+		w := httptest.NewRecorder()
+		mux.ServeHTTP(w, r)
+		if w.Code != status {
+			t.Fatalf("%s %s got %d %s want %d", method, path, w.Code, w.Body.String(), status)
+		}
+		result := response{}
+		if err := json.Unmarshal(w.Body.Bytes(), &result); err != nil {
+			t.Fatal(err)
+		}
+		return result
+	}
+	read := func() canvasModel {
+		t.Helper()
+		tx, e := db.BeginTx(ctx, nil)
+		if e != nil {
+			t.Fatal(e)
+		}
+		defer tx.Rollback()
+		model, e := loadCanvasModel(ctx, tx, project, workspace, root)
+		if e != nil {
+			t.Fatal(e)
+		}
+		return model
+	}
+	mutate := func(edit func(*canvasModel)) {
+		t.Helper()
+		tx, e := db.BeginTx(ctx, nil)
+		if e != nil {
+			t.Fatal(e)
+		}
+		defer tx.Rollback()
+		if _, _, e = lockMaterial(ctx, tx, project, workspace, root, account); e != nil {
+			t.Fatal(e)
+		}
+		before, e := loadCanvasModel(ctx, tx, project, workspace, root)
+		if e != nil {
+			t.Fatal(e)
+		}
+		after := cloneModel(before)
+		edit(&after)
+		participants := map[string]bool{}
+		for id := range after.Canvases {
+			after.Versions[id] = before.Versions[id] + 1
+			participants[id] = true
+		}
+		for id := range before.Canvases {
+			if _, active := after.Canvases[id]; !active {
+				after.Versions[id] = before.Versions[id] + 1
+				participants[id] = true
+			}
+		}
+		if e = validateCanvasModel(after); e != nil {
+			t.Fatal(e)
+		}
+		if e = s.saveCanvasModel(queueRequest(ctx), tx, project, workspace, account, before, after, participants); e != nil {
+			t.Fatal(e)
+		}
+		if e = tx.Commit(); e != nil {
+			t.Fatal(e)
+		}
+	}
+	migrationKey := modelTestID(6000)
+	migration := call("POST", base(root)+"/model/migrate", response{"protocol_version": 2, "request_id": migrationKey, "expected_versions": map[string]int64{root: 1}}, 200, 0, migrationKey)
+	node := ""
+	for _, entry := range migration["identity_map"].([]any) {
+		mapping := entry.(map[string]any)
+		if mapping["sourceId"] == "a" {
+			node = mapping["elementId"].(string)
+		}
+	}
+	if node == "" {
+		t.Fatal("missing migrated target")
+	}
+	mutate(func(model *canvasModel) {
+		model.Elements[node]["geometry"].(map[string]any)["width"] = float64(9000)
+		model.Elements[node]["opaque"] = map[string]any{"kept": true}
+		model.Elements[node]["data"].(map[string]any)["extension"] = map[string]any{"constructor": map[string]any{"kept": true}}
+		model.Elements["future"] = modelTestNode("future", root)
+		model.Elements["future"]["componentId"] = "future-component"
+		model.Elements["future"]["dataVersion"] = float64(12)
+	})
+	next := 6100
+	command := func(board, target, model string, incarnation int64) (response, string) {
+		next += 2
+		key := modelTestID(next)
+		return response{"protocol_version": 2, "request_id": key, "operation_id": modelTestID(next + 1), "target_incarnation": incarnation, "expected_versions": func() map[string]int64 {
+			model := read()
+			versions := map[string]int64{}
+			for id := range model.Canvases {
+				versions[id] = model.Versions[id]
+			}
+			return versions
+		}(), "node_id": target, "model_id": model, "prompt": "Generate", "parameters": response{}, "propagate": false}, key
+	}
+	start := func(board, target, model string, incarnation int64) response {
+		input, key := command(board, target, model, incarnation)
+		return call("POST", base(board)+"/ai/runs", input, 202, read().Versions[board], key)
+	}
+	execute := func(id string) {
+		t.Helper()
+		run, e := s.claimCanvasRun(ctx)
+		if e != nil || run == nil || run.ID != id {
+			t.Fatalf("claim %v %v", run, e)
+		}
+		s.executeCanvasRun(ctx, *run)
+	}
+	input, key := command(root, node, "text", 1)
+	sourceVersion := read().Versions[root]
+	admitted := call("POST", base(root)+"/ai/runs", input, 202, sourceVersion, key)
+	if admitted["admission"] != "accepted" || admitted["target_incarnation"] != float64(1) || admitted["model"] == nil {
+		t.Fatal("canonical admission lost identity/base")
+	}
+	retry := call("POST", base(root)+"/ai/runs", input, 202, sourceVersion, key)
+	if !modelEqual(admitted, retry) {
+		t.Fatal("admission retry changed result")
+	}
+	call("POST", base(root)+"/ai/runs", input, 409, sourceVersion+1, key)
+	queried := call("GET", base(root)+"/ai/operations/"+key, nil, 200, 0, "")
+	if !modelEqual(admitted, queried) {
+		t.Fatal("lost admission response not recoverable")
+	}
+	unknown := call("GET", base(root)+"/ai/operations/"+modelTestID(6099), nil, 404, 0, "")
+	if unknown["status"] != "unknown" || unknown["terminal"] == true {
+		t.Fatal("404 pretended zero execution")
+	}
+	duplicate := response{}
+	for k, v := range input {
+		duplicate[k] = v
+	}
+	duplicateKey := modelTestID(6098)
+	duplicate["request_id"] = duplicateKey
+	call("POST", base(root)+"/ai/runs", duplicate, 409, read().Versions[root], duplicateKey)
+	mutate(func(model *canvasModel) { model.Elements[node]["geometry"].(map[string]any)["x"] = float64(33) })
+	execute(admitted["run_id"].(string))
+	saved := read()
+	data := saved.Elements[node]["data"].(map[string]any)
+	if data["text"] != "generated result" || saved.Elements[node]["geometry"].(map[string]any)["x"] != float64(33) || saved.Elements[node]["geometry"].(map[string]any)["width"] != float64(9000) || saved.Elements["future"] == nil || saved.Elements[node]["opaque"] == nil || data["extension"] == nil {
+		t.Fatal("AI lost canonical fields, geometry or future records")
+	}
+	// A content conflict retains its output; explicit application is still a narrow canonical write.
+	conflictRun := start(root, node, "text", 1)
+	hooks <- func() {
+		mutate(func(model *canvasModel) { model.Elements[node]["data"].(map[string]any)["text"] = "user edit" })
+	}
+	execute(conflictRun["run_id"].(string))
+	conflictPath := base(root) + "/ai/runs/" + conflictRun["run_id"].(string)
+	conflict := call("GET", conflictPath, nil, 200, 0, "")
+	if conflict["status"] != "conflict" {
+		t.Fatal("changed content was overwritten")
+	}
+	outputID := conflict["outputs"].([]any)[0].(map[string]any)["output"].(map[string]any)["output_id"].(string)
+	applyKey := modelTestID(6200)
+	expected := read().Versions[root]
+	applyInput := response{"protocol_version": 2, "request_id": applyKey, "operation_id": modelTestID(6199), "target_incarnation": 1, "target_canvas_id": root, "node_id": node, "output_id": outputID}
+	applied := call("POST", conflictPath+"/apply", applyInput, 200, expected, applyKey)
+	again := call("POST", conflictPath+"/apply", applyInput, 200, expected, applyKey)
+	if !modelEqual(applied, again) || applied["model"] == nil || read().Elements[node]["geometry"].(map[string]any)["width"] != float64(9000) {
+		t.Fatal("explicit canonical application changed geometry or receipt")
+	}
+	applyReceipt := call("GET", base(root)+"/ai/operations/"+applyKey, nil, 200, 0, "")
+	if !modelEqual(applied, applyReceipt) || applied["action"] != "run.apply" || applied["status"] != "applied" {
+		t.Fatal("explicit apply receipt is not recoverable")
+	}
+	call("POST", conflictPath+"/apply", applyInput, 409, expected+1, applyKey)
+	// Keep one unapplied old output, then replace the target incarnation atomically.
+	stale := start(root, node, "text", 1)
+	hooks <- func() {
+		mutate(func(model *canvasModel) { model.Elements[node]["data"].(map[string]any)["text"] = "keep this" })
+	}
+	execute(stale["run_id"].(string))
+	stalePath := base(root) + "/ai/runs/" + stale["run_id"].(string)
+	staleResult := call("GET", stalePath, nil, 200, 0, "")
+	staleOutput := staleResult["outputs"].([]any)[0].(map[string]any)["output"].(map[string]any)["output_id"].(string)
+	old := start(root, node, "text", 1)
+	run, e := s.claimCanvasRun(ctx)
+	if e != nil || run == nil || run.ID != old["run_id"] {
+		t.Fatalf("claim stale %v", e)
+	}
+	if ok, e := s.startCanvasStep(ctx, *run, run.Plan.Steps[0]); e != nil || !ok {
+		t.Fatalf("start stale %v", e)
+	}
+	mutate(func(model *canvasModel) {
+		model.Elements[node]["incarnation"] = float64(2)
+		model.Tombstones[node] = 1
+		model.TombstoneOwners[node] = root
+	})
+	state, e := s.finishCanvasStep(ctx, *run, run.Plan.Steps[0], "late output", "", true)
+	if e != nil || state != "cancelled" {
+		t.Fatalf("restored target accepted old callback %s %v", state, e)
+	}
+	if e = s.completeCanvasRun(ctx, *run, nil); e != nil {
+		t.Fatal(e)
+	}
+	if read().Elements[node]["data"].(map[string]any)["text"] != "keep this" {
+		t.Fatal("restore was overwritten")
+	}
+	staleApplyKey := modelTestID(6201)
+	staleApply := call("POST", stalePath+"/apply", response{"protocol_version": 2, "request_id": staleApplyKey, "operation_id": modelTestID(6205), "target_incarnation": 1, "target_canvas_id": root, "node_id": node, "output_id": staleOutput}, 409, read().Versions[root], staleApplyKey)
+	if staleApply["status"] != "not-applied" || staleApply["terminal"] != true || !modelEqual(staleApply, call("GET", base(root)+"/ai/operations/"+staleApplyKey, nil, 200, 0, "")) {
+		t.Fatal("stale apply has no queryable zero-effect receipt")
+	}
+
+	bad, badKey := command(root, node, "text", 1)
+	call("POST", base(root)+"/ai/runs", bad, 409, read().Versions[root], badKey)
+	restored := start(root, node, "text", 2)
+	cancelPath := base(root) + "/ai/runs/" + restored["run_id"].(string) + "/cancel"
+	cancelKey := modelTestID(6202)
+	cancelInput := response{"protocol_version": 2, "request_id": cancelKey, "operation_id": modelTestID(6203)}
+	cancelled := call("POST", cancelPath, cancelInput, 200, 0, cancelKey)
+	cancelAgain := call("POST", cancelPath, cancelInput, 200, 0, cancelKey)
+	cancelReceipt := call("GET", base(root)+"/ai/operations/"+cancelKey, nil, 200, 0, "")
+	if cancelled["status"] != "applied" || cancelled["run_status"] != "cancelled" || !modelEqual(cancelled, cancelAgain) || !modelEqual(cancelled, cancelReceipt) {
+		t.Fatal("cancel receipt changed on retry/query")
+	}
+	duplicateCancelKey := modelTestID(6204)
+	call("POST", cancelPath, response{"protocol_version": 2, "request_id": duplicateCancelKey, "operation_id": modelTestID(6203)}, 409, 0, duplicateCancelKey)
+	if executions.Load() != 3 {
+		t.Fatal("duplicate/cancelled/old execution called the model")
+	}
+	// Image output resolves a managed resource while retaining the element envelope.
+	imageID := modelTestID(6300)
+	mutate(func(model *canvasModel) {
+		record := modelTestNode(imageID, root)
+		record["componentId"] = "plain-image"
+		record["data"].(map[string]any)["src"] = "data:image/png;base64," + base64.StdEncoding.EncodeToString(pngBytes.Bytes())
+		record["geometry"].(map[string]any)["width"] = float64(10000)
+		model.Elements[imageID] = record
+	})
+	imageRun := start(root, imageID, "image", 1)
+	execute(imageRun["run_id"].(string))
+	imageRecord := read().Elements[imageID]
+	imageData := imageRecord["data"].(map[string]any)
+	if imageRecord["geometry"].(map[string]any)["width"] != float64(10000) || imageData["assetId"] == nil || !strings.HasPrefix(modelString(imageData["src"]), s.assetURL(project, workspace, "")) {
+		t.Fatal("image result lost geometry or resource identity")
+	}
+	request := httptest.NewRequest("GET", modelString(imageData["src"]), nil)
+	request.Header.Set("Authorization", "Bearer "+token)
+	download := httptest.NewRecorder()
+	mux.ServeHTTP(download, request)
+	if download.Code != 200 || !bytes.Equal(download.Body.Bytes(), pngBytes.Bytes()) {
+		t.Fatal("canonical generated asset is unreadable")
+	}
+	moved := start(root, imageID, "image", 1)
+	moving, e := s.claimCanvasRun(ctx)
+	if e != nil || moving == nil || moving.ID != moved["run_id"] {
+		t.Fatalf("claim move %v", e)
+	}
+	if ok, e := s.startCanvasStep(ctx, *moving, moving.Plan.Steps[0]); e != nil || !ok {
+		t.Fatalf("start move %v", e)
+	}
+	child, frame := modelTestID(6301), modelTestID(6302)
+	mutate(func(model *canvasModel) {
+		entry := modelTestNode(frame, root)
+		entry["componentId"] = "frame"
+		model.Elements[frame] = entry
+		model.Canvases[child] = modelCanvas{ID: child, Parent: &modelParent{CanvasID: root, EntryElementID: frame}}
+		model.Elements[imageID]["ownerCanvasId"] = child
+	})
+	busyInput, busyKey := command(child, imageID, "image", 1)
+	busy := call("POST", base(child)+"/ai/runs", busyInput, 409, read().Versions[child], busyKey)
+	if busy["error"] != "node_busy" {
+		t.Fatal("owner move admitted a duplicate paid task")
+	}
+	beforeMovedOutput := read()
+	state, e = s.finishCanvasStepOutput(ctx, *moving, moving.Plan.Steps[0], codex.CanvasOutput{Kind: "image", Image: &codex.CanvasImage{MIME: "image/png", Data: pngBytes.Bytes()}}, "", true)
+	if e != nil || state != "succeeded" {
+		t.Fatalf("owner-only move rejected output %s %v", state, e)
+	}
+	afterMovedOutput := read()
+	if afterMovedOutput.Elements[imageID]["ownerCanvasId"] != child || afterMovedOutput.Versions[root] != beforeMovedOutput.Versions[root] || afterMovedOutput.Versions[child] != beforeMovedOutput.Versions[child]+1 || afterMovedOutput.Elements[imageID]["geometry"].(map[string]any)["width"] != float64(10000) {
+		t.Fatal("relocated result rewrote ownership, geometry or the origin version")
+	}
+	movedStatus := call("GET", base(root)+"/ai/runs/"+moving.ID, nil, 200, 0, "")
+	foundRelocation := false
+	for _, value := range movedStatus["events"].([]any) {
+		event := value.(map[string]any)
+		if event["type"] == "step.applied" {
+			foundRelocation = event["board_id"] == child && event["origin_board_id"] == root && event["canonical_root"] == root && event["model"].(map[string]any)["complete"] == true
+		}
+	}
+	if !foundRelocation || movedStatus["applied_versions"].(map[string]any)[child] != float64(afterMovedOutput.Versions[child]) {
+		t.Fatal("moved output lost current-owner version or canonical context")
+	}
+
+	if e = s.completeCanvasRun(ctx, *moving, nil); e != nil {
+		t.Fatal(e)
+	}
+	staleInput, staleKey := command(child, imageID, "image", 1)
+	staleVersions := staleInput["expected_versions"].(map[string]int64)
+	staleVersions[root]-- // The target version is current; its ancestor context is not.
+	beforeRejected := read()
+	denied := call("POST", base(child)+"/ai/runs", staleInput, 412, read().Versions[child], staleKey)
+	if denied["status"] != "not-applied" || denied["terminal"] != true || denied["action"] != "run.start" || !modelEqual(beforeRejected, read()) {
+		t.Fatal("rejection was not a zero-effect receipt")
+	}
+	if queried := call("GET", base(child)+"/ai/operations/"+staleKey, nil, 200, 0, ""); !modelEqual(denied, queried) {
+		t.Fatal("negative admission receipt lost")
+	}
+	// A later context change cannot turn an old rejected key into a paid execution.
+	mutate(func(model *canvasModel) { model.Elements[imageID]["geometry"].(map[string]any)["x"] = float64(123) })
+	if retried := call("POST", base(child)+"/ai/runs", staleInput, 412, beforeRejected.Versions[child], staleKey); !modelEqual(denied, retried) {
+		t.Fatal("rejected request was reevaluated")
+	}
+	missingRunKey := modelTestID(6400)
+	missingCancel := call("POST", base(child)+"/ai/runs/"+modelTestID(6401)+"/cancel", response{"protocol_version": 2, "request_id": missingRunKey, "operation_id": modelTestID(6402)}, 404, 0, missingRunKey)
+	if missingCancel["status"] != "not-applied" || missingCancel["terminal"] != true {
+		t.Fatal("missing run cancel has no stable rejection")
+	}
+	if queried := call("GET", base(child)+"/ai/operations/"+missingRunKey, nil, 200, 0, ""); !modelEqual(missingCancel, queried) {
+		t.Fatal("negative cancel receipt lost")
+	}
+	missingInput, missingKey := command(child, imageID, "image", 1)
+	delete(missingInput, "expected_versions")
+	call("POST", base(child)+"/ai/runs", missingInput, 400, read().Versions[child], missingKey)
+	// An explicit replan can reuse a logical operation after its known zero-effect rejection.
+	replanned := response{}
+	for key, value := range staleInput {
+		replanned[key] = value
+	}
+	replanKey := modelTestID(6405)
+	replanned["request_id"], replanned["expected_versions"] = replanKey, read().Versions
+	childRun := call("POST", base(child)+"/ai/runs", replanned, 202, read().Versions[child], replanKey)
+
+	execute(childRun["run_id"].(string))
+	beforeLateCancel := read()
+	lateKey := modelTestID(6406)
+	lateCancel := call("POST", base(child)+"/ai/runs/"+childRun["run_id"].(string)+"/cancel", response{"protocol_version": 2, "request_id": lateKey, "operation_id": modelTestID(6407)}, 200, 0, lateKey)
+	if lateCancel["run_status"] != "succeeded" || !modelEqual(beforeLateCancel, read()) {
+		t.Fatal("late cancellation pretended to undo a completed result")
+	}
+	if read().Elements[imageID]["ownerCanvasId"] != child {
+		t.Fatal("child result moved its target back")
+	}
+	queuedMove := start(child, imageID, "image", 1)
+	mutate(func(model *canvasModel) {
+		model.Elements[imageID]["ownerCanvasId"] = root
+		delete(model.Canvases, child)
+	})
+	execute(queuedMove["run_id"].(string))
+	archivedRoute := base(child) + "/ai/runs/" + queuedMove["run_id"].(string)
+	archivedResult := call("GET", archivedRoute, nil, 200, 0, "")
+	if archivedResult["status"] != "succeeded" || read().Elements[imageID]["ownerCanvasId"] != root {
+		t.Fatal("queued move or archived admission route stopped the run")
+	}
+	lateArchiveKey := modelTestID(6500)
+	if result := call("POST", archivedRoute+"/cancel", response{"protocol_version": 2, "request_id": lateArchiveKey, "operation_id": modelTestID(6501)}, 200, 0, lateArchiveKey); result["run_status"] != "succeeded" {
+		t.Fatal("archived route lost cancellation identity")
+	}
+	// Content changes still conflict after a move; explicit application targets the current owner.
+	movedConflict := start(root, node, "text", 2)
+	hooks <- func() {
+		mutate(func(model *canvasModel) {
+			model.Canvases[child] = modelCanvas{ID: child, Parent: &modelParent{CanvasID: root, EntryElementID: frame}}
+			model.Elements[node]["ownerCanvasId"] = child
+			model.Elements[node]["data"].(map[string]any)["text"] = "keep moved edit"
+		})
+	}
+	execute(movedConflict["run_id"].(string))
+	movedConflictPath := base(root) + "/ai/runs/" + movedConflict["run_id"].(string)
+	conflictMovedResult := call("GET", movedConflictPath, nil, 200, 0, "")
+	if conflictMovedResult["status"] != "conflict" || read().Elements[node]["data"].(map[string]any)["text"] != "keep moved edit" {
+		t.Fatal("move allowed a content conflict overwrite")
+	}
+	movedOutput := conflictMovedResult["outputs"].([]any)[0].(map[string]any)["output"].(map[string]any)["output_id"].(string)
+	movedApplyKey := modelTestID(6502)
+	movedApplied := call("POST", movedConflictPath+"/apply", response{"protocol_version": 2, "request_id": movedApplyKey, "operation_id": modelTestID(6503), "node_id": node, "output_id": movedOutput, "target_incarnation": 2, "target_canvas_id": child}, 200, read().Versions[child], movedApplyKey)
+	if movedApplied["board_id"] != child || movedApplied["origin_board_id"] != root || read().Elements[node]["ownerCanvasId"] != child {
+		t.Fatal("explicit application wrote to the frozen owner")
+	}
+	doomed := start(child, node, "text", 2)
+	mutate(func(model *canvasModel) {
+		record := model.Elements[node]
+		model.DeadRecords[node] = record
+		model.Tombstones[node] = 2
+		model.TombstoneOwners[node] = child
+		delete(model.Elements, node)
+		for id, element := range model.Elements {
+			if element["structure"] == "connection" && (element["source"].(map[string]any)["elementId"] == node || element["target"].(map[string]any)["elementId"] == node) {
+				model.DeadRecords[id] = element
+				model.Tombstones[id] = modelInt(element["incarnation"])
+				model.TombstoneOwners[id] = modelString(element["ownerCanvasId"])
+				delete(model.Elements, id)
+			}
+		}
+	})
+	execute(doomed["run_id"].(string))
+	if result := call("GET", base(child)+"/ai/runs/"+doomed["run_id"].(string), nil, 200, 0, ""); result["status"] != "cancelled" {
+		t.Fatal("deleting a moved target failed to revoke its old job")
+	}
+
+	revoked := start(root, imageID, "image", 1)
+	mutate(func(model *canvasModel) { model.Elements[imageID]["ownerCanvasId"] = child })
+	beforeRevoked := executions.Load()
+	if _, e = db.ExecContext(ctx, `UPDATE workspace_members SET role='viewer' WHERE project=$1 AND workspace_id=$2 AND account_id=$3`, project, workspace, account); e != nil {
+		t.Fatal(e)
+	}
+	execute(revoked["run_id"].(string))
+	if result := call("GET", base(root)+"/ai/runs/"+revoked["run_id"].(string), nil, 200, 0, ""); result["status"] != "failed" || executions.Load() != beforeRevoked {
+		t.Fatal("moved target executed after write permission was revoked")
+	}
+
+}

internal/platform/canvas_ai_model_test.go

@@ -0,0 +1,97 @@
+package platform
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestCanonicalAIPatchPreservesOpaqueModelAndGeometry(t *testing.T) {
+	before := modelTestDocument()
+	before.Elements["a"]["geometry"].(map[string]any)["width"] = float64(9000)
+	before.Elements["a"]["extension"] = map[string]any{"kept": true}
+	before.Elements["a"]["data"].(map[string]any)["opaque"] = map[string]any{"constructor": map[string]any{"kept": true}}
+	before.Elements["future"] = modelTestNode("future", modelRootID)
+	before.Elements["future"]["dataVersion"] = float64(12)
+	original := cloneModel(before)
+	after, err := prepareModelAIPatch(before, modelRootID, "a", response{"text": "generated"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !modelEqual(before, original) {
+		t.Fatal("AI staging changed its source")
+	}
+	if after.Elements["a"]["data"].(map[string]any)["text"] != "generated" || after.Versions[modelRootID] != 2 {
+		t.Fatal("AI text/version missing")
+	}
+	if !modelEqual(after.Elements["a"]["geometry"], before.Elements["a"]["geometry"]) || !modelEqual(after.Elements["a"]["extension"], before.Elements["a"]["extension"]) || !modelEqual(after.Elements["future"], before.Elements["future"]) {
+		t.Fatal("AI staging replaced unrelated fields")
+	}
+	if _, err = prepareModelAIPatch(before, modelRootID, "a", response{"geometry": map[string]any{}}); err != errAIInvalidPatch {
+		t.Fatalf("geometry patch was accepted: %v", err)
+	}
+	if _, err = prepareModelAIPatch(before, modelRootID, "future", response{"text": "lost"}); err != errAITargetChanged {
+		t.Fatalf("future schema was interpreted: %v", err)
+	}
+	if _, err = prepareModelAIPatch(before, modelChildID, "a", response{"text": "wrong owner"}); err != errAITargetChanged {
+		t.Fatalf("wrong owner was accepted: %v", err)
+	}
+}
+
+func TestCanonicalAIProjectionDoesNotExecuteFutureConnections(t *testing.T) {
+	model := modelTestDocument()
+	model.Elements["b"] = modelTestNode("b", modelRootID)
+	model.Elements["future-edge"] = map[string]any{"id": "future-edge", "incarnation": float64(1), "structure": "connection", "componentId": "connection", "dataVersion": float64(9), "ownerCanvasId": modelRootID, "source": map[string]any{"elementId": "a"}, "target": map[string]any{"elementId": "b"}, "path": nil, "data": map[string]any{}}
+	if err := validateCanvasModel(model); err != nil {
+		t.Fatal(err)
+	}
+	projection, err := projectCanvasModel(model)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var document map[string]any
+	if err = json.Unmarshal(projection[modelRootID], &document); err != nil {
+		t.Fatal(err)
+	}
+	if len(document["edges"].([]any)) != 0 || model.Elements["future-edge"] == nil {
+		t.Fatal("future connection was executed or removed")
+	}
+}
+
+func TestCanonicalAIAdmissionVersions(t *testing.T) {
+	model := modelTestDocument()
+	model.Canvases[modelChildID] = modelCanvas{ID: modelChildID}
+	model.Versions[modelChildID] = 3
+	// Include an archived version: it must not become an executable read dependency.
+	model.Versions["archived"] = 8
+	valid := map[string]int64{}
+	for id := range model.Canvases {
+		valid[id] = model.Versions[id]
+	}
+	if code := validateCanvasAIVersions(model, modelRootID, valid[modelRootID], valid); code != "" {
+		t.Fatal(code)
+	}
+	for _, test := range []struct {
+		name     string
+		versions map[string]int64
+		header   int64
+		want     string
+	}{
+		{"missing", nil, 1, "invalid_ai_versions"},
+		{"changed-header", valid, 99, "invalid_ai_versions"},
+		{"incomplete", map[string]int64{modelRootID: 1}, 1, "invalid_ai_versions"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			if got := validateCanvasAIVersions(model, modelRootID, test.header, test.versions); got != test.want {
+				t.Fatalf("got %q want %q", got, test.want)
+			}
+		})
+	}
+	stale := map[string]int64{}
+	for id, version := range valid {
+		stale[id] = version
+	}
+	stale[modelChildID]++
+	if code := validateCanvasAIVersions(model, modelRootID, valid[modelRootID], stale); code != "version_conflict" {
+		t.Fatal(code)
+	}
+}

internal/platform/canvas_ai_plan.go

@@ -15,18 +15,20 @@ type canvasAIStaticInput struct {
 	Content map[string]any `json:"content"`
 }
 type canvasAIStepPlan struct {
-	StaticInputs   []canvasAIStaticInput `json:"static_inputs"`
-	MaxExecutionMS int                   `json:"max_execution_ms"`
-	ID             string                `json:"step_id"`
-	BoardID        string                `json:"board_id"`
-	NodeID         string                `json:"node_id"`
-	Kind           string                `json:"kind"`
-	ModelID        string                `json:"model_id"`
-	Config         map[string]any        `json:"config"`
-	FrozenContent  map[string]any        `json:"frozen_content"`
-	Fingerprint    string                `json:"target_fingerprint"`
-	Status         string                `json:"status"`
-	Dependencies   []string              `json:"dependencies"`
+	CanonicalRoot     string                `json:"canonical_root,omitempty"`
+	TargetIncarnation int64                 `json:"target_incarnation,omitempty"`
+	StaticInputs      []canvasAIStaticInput `json:"static_inputs"`
+	MaxExecutionMS    int                   `json:"max_execution_ms"`
+	ID                string                `json:"step_id"`
+	BoardID           string                `json:"board_id"`
+	NodeID            string                `json:"node_id"`
+	Kind              string                `json:"kind"`
+	ModelID           string                `json:"model_id"`
+	Config            map[string]any        `json:"config"`
+	FrozenContent     map[string]any        `json:"frozen_content"`
+	Fingerprint       string                `json:"target_fingerprint"`
+	Status            string                `json:"status"`
+	Dependencies      []string              `json:"dependencies"`
 }
 type canvasAIEdgePlan struct {
 	ID     string `json:"logical_edge_id"`

internal/platform/canvas_ai_query.go

@@ -14,7 +14,7 @@ func publicAIPlan(plan canvasAIPlan) response {
 		for _, source := range step.StaticInputs {
 			static = append(static, response{"logical_edge_id": source.EdgeID, "board_id": source.BoardID, "node_id": source.NodeID, "kind": source.Kind, "source": "frozen_snapshot"})
 		}
-		steps = append(steps, response{"step_id": step.ID, "board_id": step.BoardID, "node_id": step.NodeID, "kind": step.Kind, "model_id": step.ModelID, "max_execution_ms": step.MaxExecutionMS, "status": step.Status, "dependencies": step.Dependencies, "static_inputs": static})
+		steps = append(steps, response{"step_id": step.ID, "board_id": step.BoardID, "node_id": step.NodeID, "target_incarnation": step.TargetIncarnation, "canonical_root": step.CanonicalRoot, "kind": step.Kind, "model_id": step.ModelID, "max_execution_ms": step.MaxExecutionMS, "status": step.Status, "dependencies": step.Dependencies, "static_inputs": static})
 	}
 	return response{"steps": steps, "edges": plan.Edges, "frozen_versions": plan.Versions}
 }
@@ -51,7 +51,7 @@ func (s *service) getCanvasAIRun(w http.ResponseWriter, r *http.Request, project
 		return err
 	}
 	defer tx.Rollback()
-	if _, _, err = lockMaterial(r.Context(), tx, project, workspace, board, account); err != nil {
+	if _, _, err = lockCanvasAIRunRoute(r.Context(), tx, project, workspace, board, account); err != nil {
 		return err
 	}
 	var status string
@@ -68,14 +68,21 @@ func (s *service) getCanvasAIRun(w http.ResponseWriter, r *http.Request, project
 	}
 	checked := map[string]bool{board: true}
 	for _, step := range plan.Steps {
-		if !checked[step.BoardID] {
-			if _, _, err = lockMaterial(r.Context(), tx, project, workspace, step.BoardID, account); err != nil {
-				return err
+		target, ok, e := resolveCanvasAITarget(r.Context(), tx, project, workspace, step)
+		if e != nil {
+			return e
+		}
+		if !ok {
+			target = step.BoardID
+		}
+		if !checked[target] {
+			if _, _, e = lockCanvasAIRunRoute(r.Context(), tx, project, workspace, target, account); e != nil {
+				return e
 			}
-			checked[step.BoardID] = true
+			checked[target] = true
 		}
 	}
-	rows, err := tx.QueryContext(r.Context(), `SELECT id,board_id::text,node_id,status,error_code,applied_version,CASE WHEN output IS NULL THEN NULL ELSE output-'text' END FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND run_id=$3 ORDER BY ordinal`, project, workspace, id)
+	rows, err := tx.QueryContext(r.Context(), `SELECT id,COALESCE(applied_board_id,board_id)::text,node_id,status,error_code,applied_version,CASE WHEN output IS NULL THEN NULL ELSE output-'text' END FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND run_id=$3 ORDER BY ordinal`, project, workspace, id)
 	if err != nil {
 		return err
 	}
@@ -158,3 +165,45 @@ func (s *service) getCanvasAIRun(w http.ResponseWriter, r *http.Request, project
 	reply(w, 200, result)
 	return nil
 }
+
+// Resolve admission by the original client key, before the caller knows a run ID.
+// Absence is unknown, not a terminal proof that an earlier invocation had no effect.
+func (s *service) getCanvasAIAdmission(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	key := r.PathValue("request")
+	if !uuidSlugPattern.MatchString(key) {
+		reject(w, 400, "invalid_request_id")
+		return nil
+	}
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	if _, _, err = lockCanvasAIRunRoute(r.Context(), tx, project, workspace, board, account); err != nil {
+		return err
+	}
+	var body json.RawMessage
+	err = tx.QueryRowContext(r.Context(), `SELECT response_body FROM canvas_ai_requests WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND account_id=$4 AND request_id=$5`, project, workspace, board, account, key).Scan(&body)
+	if err == nil {
+		reply(w, 200, body)
+		return nil
+	}
+	if err != sql.ErrNoRows {
+		return err
+	}
+	err = tx.QueryRowContext(r.Context(), `SELECT create_response FROM canvas_ai_runs WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND account_id=$4 AND idempotency_key=$5`, project, workspace, board, account, key).Scan(&body)
+	if err == sql.ErrNoRows {
+		reply(w, 404, response{"protocol_version": 2, "request_id": key, "status": "unknown", "error": "ai_admission_unknown"})
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	reply(w, 200, body)
+	return nil
+}

internal/platform/canvas_ai_receipts.go

@@ -0,0 +1,83 @@
+package platform
+
+import (
+	"database/sql"
+	"encoding/json"
+	"net/http"
+)
+
+type canvasAIRequest struct {
+	Key, Hash, Action, Board, Run, Operation string
+}
+
+// The workspace lock is acquired by the caller before this savepoint. Rejected
+// requests roll back every staged effect and retain that lock while recording
+// their zero-effect receipt, so a response can never race a second invocation.
+func beginCanvasAIRequest(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, workspace, account string, request *canvasAIRequest) (bool, error) {
+	if request == nil {
+		return false, nil
+	}
+	var board, run, action, hash string
+	var status int
+	var body json.RawMessage
+	err := tx.QueryRowContext(r.Context(), `SELECT board_id::text,COALESCE(run_id::text,''),action,payload_hash,response_status,response_body FROM canvas_ai_requests WHERE project=$1 AND workspace_id=$2 AND account_id=$3 AND request_id=$4`, project, workspace, account, request.Key).Scan(&board, &run, &action, &hash, &status, &body)
+	if err == nil {
+		if board != request.Board || run != request.Run || action != request.Action || hash != request.Hash {
+			reject(w, 409, "idempotency_conflict")
+			return true, nil
+		}
+		reply(w, status, body)
+		return true, nil
+	}
+	if err != sql.ErrNoRows {
+		return false, err
+	}
+	var completed bool
+	err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_requests WHERE project=$1 AND workspace_id=$2 AND account_id=$3 AND operation_id=$4 AND outcome='applied')`, project, workspace, account, request.Operation).Scan(&completed)
+	if err != nil {
+		return false, err
+	}
+	if completed {
+		reject(w, 409, "operation_identity_conflict")
+		return true, nil
+	}
+	_, err = tx.ExecContext(r.Context(), `SAVEPOINT canvas_ai_effects`)
+	return false, err
+}
+func bindCanvasAIReceipt(body response, request *canvasAIRequest) {
+	if request == nil {
+		return
+	}
+	body["protocol_version"], body["request_id"], body["operation_id"], body["action"] = 2, request.Key, request.Operation, request.Action
+	if request.Run != "" {
+		body["run_id"] = request.Run
+	}
+}
+func commitCanvasAIReceipt(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, workspace, account string, request *canvasAIRequest, status int, outcome string, body response) error {
+	if request != nil {
+		bindCanvasAIReceipt(body, request)
+		raw, err := json.Marshal(body)
+		if err != nil {
+			return err
+		}
+		_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_ai_requests(project,workspace_id,account_id,request_id,board_id,run_id,action,operation_id,payload_hash,outcome,response_status,response_body) VALUES($1,$2,$3,$4,$5,NULLIF($6,'')::uuid,$7,$8,$9,$10,$11,$12)`, project, workspace, account, request.Key, request.Board, request.Run, request.Action, request.Operation, request.Hash, outcome, status, raw)
+		if err != nil {
+			return err
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	reply(w, status, body)
+	return nil
+}
+func rejectCanvasAIRequest(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, workspace, account string, request *canvasAIRequest, status int, code string) error {
+	if request == nil {
+		reject(w, status, code)
+		return nil
+	}
+	if _, err := tx.ExecContext(r.Context(), `ROLLBACK TO SAVEPOINT canvas_ai_effects`); err != nil {
+		return err
+	}
+	return commitCanvasAIReceipt(w, r, tx, project, workspace, account, request, status, "not-applied", response{"status": "not-applied", "terminal": true, "error": code})
+}

internal/platform/canvas_ai_runs.go

@@ -47,11 +47,16 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		return nil
 	}
 	var input struct {
-		NodeID     string         `json:"node_id"`
-		ModelID    string         `json:"model_id"`
-		Prompt     string         `json:"prompt"`
-		Parameters map[string]any `json:"parameters"`
-		Propagate  bool           `json:"propagate"`
+		ProtocolVersion   int              `json:"protocol_version,omitempty"`
+		OperationID       string           `json:"operation_id,omitempty"`
+		RequestID         string           `json:"request_id,omitempty"`
+		TargetIncarnation int64            `json:"target_incarnation,omitempty"`
+		ExpectedVersions  map[string]int64 `json:"expected_versions,omitempty"`
+		NodeID            string           `json:"node_id"`
+		ModelID           string           `json:"model_id"`
+		Prompt            string           `json:"prompt"`
+		Parameters        map[string]any   `json:"parameters"`
+		Propagate         bool             `json:"propagate"`
 	}
 	decoder := json.NewDecoder(bytes.NewReader(raw))
 	decoder.DisallowUnknownFields()
@@ -59,6 +64,10 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		reject(w, 400, "invalid_ai_request")
 		return nil
 	}
+	if input.OperationID != "" && !uuidSlugPattern.MatchString(input.OperationID) {
+		reject(w, 400, "invalid_ai_request")
+		return nil
+	}
 	if input.Parameters == nil {
 		input.Parameters = map[string]any{}
 	}
@@ -68,6 +77,10 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		return nil
 	}
 	hash := payloadDigest(input)
+	if input.ProtocolVersion != 0 {
+		// The version header is part of the immutable canonical admission request.
+		hash = payloadDigest(response{"input": input, "if_match": expected})
+	}
 	workspace, board := r.PathValue("workspace"), r.PathValue("material")
 	tx, err := s.db.BeginTx(r.Context(), nil)
 	if err != nil {
@@ -78,13 +91,21 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	if err != nil {
 		return err
 	}
+	var receipt *canvasAIRequest
+	if input.ProtocolVersion == 2 && input.RequestID == key && uuidSlugPattern.MatchString(input.OperationID) && input.TargetIncarnation > 0 {
+		receipt = &canvasAIRequest{Key: key, Hash: hash, Action: "run.start", Board: board, Operation: input.OperationID}
+		if done, e := beginCanvasAIRequest(w, r, tx, project, workspace, account, receipt); done || e != nil {
+			return e
+		}
+	}
+	rejectRequest := func(status int, code string) error {
+		return rejectCanvasAIRequest(w, r, tx, project, workspace, account, receipt, status, code)
+	}
 	if kind != "board" {
-		reject(w, 400, "invalid_material")
-		return nil
+		return rejectRequest(400, "invalid_material")
 	}
 	if role == "viewer" {
-		reject(w, 403, "forbidden")
-		return nil
+		return rejectRequest(403, "forbidden")
 	}
 	var previousHash string
 	var previous json.RawMessage
@@ -105,13 +126,22 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	if err != sql.ErrNoRows {
 		return err
 	}
+	if input.OperationID != "" {
+		var admitted bool
+		if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_runs WHERE project=$1 AND workspace_id=$2 AND account_id=$3 AND logical_operation_id=$4)`, project, workspace, account, input.OperationID).Scan(&admitted); err != nil {
+			return err
+		}
+		if admitted {
+			reject(w, 409, "operation_identity_conflict")
+			return nil
+		}
+	}
 	parent, err := loadCanvas(r, tx, project, workspace, board)
 	if err != nil {
 		return err
 	}
 	if parent.Version != expected {
-		reject(w, 412, "version_conflict")
-		return nil
+		return rejectRequest(412, "version_conflict")
 	}
 	var doc map[string]any
 	_ = json.Unmarshal(parent.Document, &doc)
@@ -123,42 +153,59 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		}
 	}
 	if target == nil {
-		reject(w, 404, "not_found")
-		return nil
+		return rejectRequest(404, "not_found")
 	}
 	if !canvasChoice(target["kind"], "text", "script", "plain-text", "image", "plain-image") {
-		reject(w, 422, "model_incompatible")
-		return nil
+		return rejectRequest(422, "model_incompatible")
 	}
-	target["ai"] = map[string]any{"enabled": true, "modelId": input.ModelID, "prompt": input.Prompt, "parameters": input.Parameters, "propagate": input.Propagate}
-	doc["schema_version"] = 2
-	encoded, _ := json.Marshal(doc)
-	normalized, ok := normalizeCanvas(encoded)
-	if !ok {
-		reject(w, 400, "invalid_ai_request")
-		return nil
+	root, incarnation, _, err := canvasAIIdentity(r.Context(), tx, project, workspace, board, input.NodeID)
+	if err != nil {
+		return err
+	}
+	if root != "" {
+		if input.ProtocolVersion != 2 || input.RequestID != key || !uuidSlugPattern.MatchString(input.OperationID) || input.TargetIncarnation < 1 {
+			return rejectRequest(400, "invalid_ai_protocol")
+		}
+		if input.TargetIncarnation != incarnation {
+			return rejectRequest(409, "target_changed")
+		}
+	} else if input.ProtocolVersion != 0 || input.RequestID != "" || input.TargetIncarnation != 0 || input.OperationID != "" || input.ExpectedVersions != nil {
+		return rejectRequest(409, "canonical_migration_required")
+	}
+	change, err := prepareCanvasAIPatch(r, tx, project, workspace, parent, input.NodeID, response{"ai": map[string]any{"enabled": true, "modelId": input.ModelID, "prompt": input.Prompt, "parameters": input.Parameters, "propagate": input.Propagate}})
+	if err != nil {
+		return rejectRequest(400, "invalid_ai_request")
+	}
+	if change.Before != nil {
+		if code := validateCanvasAIVersions(*change.Before, board, expected, input.ExpectedVersions); code != "" {
+			status := http.StatusBadRequest
+			if code == "version_conflict" {
+				status = http.StatusPreconditionFailed
+			}
+			return rejectRequest(status, code)
+		}
 	}
 	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
 	defer cancel()
 	models, err := s.canvasAI.Models(ctx)
 	if err != nil {
-		reject(w, 503, "codex_unavailable")
-		return nil
+		return rejectRequest(503, "codex_unavailable")
 	}
 	catalogue := map[string]codex.CanvasModel{}
 	for _, model := range models {
 		catalogue[model.ID] = model
 	}
-	parent.Document = normalized
-	parent.Version++
+	parent = change.Snapshot
 	plan, err := loadCanvasAIPlan(r, tx, project, workspace, account, parent, input.NodeID, input.Propagate)
 	if err != nil {
 		if err.Error() == "execution_cycle" {
-			reject(w, 409, "execution_cycle")
+			return rejectRequest(409, "execution_cycle")
 		} else {
-			reject(w, 413, "graph_limit_exceeded")
+			return rejectRequest(413, "graph_limit_exceeded")
 		}
-		return nil
+	}
+	if err = bindCanvasAIIdentities(r.Context(), tx, project, workspace, &plan); err != nil {
+		return err
 	}
 	stepKinds := map[string]string{}
 	for _, step := range plan.Steps {
@@ -173,16 +220,14 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		}
 		model, exists := catalogue[step.ModelID]
 		if !exists || !model.Available {
-			reject(w, 422, "model_unavailable")
-			return nil
+			return rejectRequest(422, "model_unavailable")
 		}
 		modality := "text"
 		if canvasChoice(step.Kind, "image", "plain-image") {
 			modality = "image"
 		}
 		if !canvasModelSupports(model, modality) {
-			reject(w, 422, "model_incompatible")
-			return nil
+			return rejectRequest(422, "model_incompatible")
 		}
 		imageSources := map[string]bool{}
 		if canvasChoice(step.Kind, "image", "plain-image") {
@@ -199,12 +244,10 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			}
 		}
 		if len(imageSources) > 0 && !canvasModelAccepts(model, "image") {
-			reject(w, 422, "model_incompatible")
-			return nil
+			return rejectRequest(422, "model_incompatible")
 		}
 		if len(imageSources) > 4 {
-			reject(w, 413, "context_too_large")
-			return nil
+			return rejectRequest(413, "context_too_large")
 		}
 		plan.Steps[index].MaxExecutionMS = model.MaxExecutionMS
 		if canvasChoice(step.Kind, "image", "plain-image") {
@@ -215,8 +258,7 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 				frozenImages[step.ID] = content
 			}
 			if e != nil {
-				reject(w, 422, "model_incompatible")
-				return nil
+				return rejectRequest(422, "model_incompatible")
 			}
 			plan.Steps[index].FrozenContent = content
 		}
@@ -233,35 +275,34 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 				frozenImages[key] = content
 			}
 			if e != nil {
-				reject(w, 422, "model_incompatible")
-				return nil
+				return rejectRequest(422, "model_incompatible")
 			}
 			plan.Steps[index].StaticInputs[staticIndex].Content = content
 		}
 		if _, e := assembleCanvasTask(plan, plan.Steps[index], nil); e != nil {
-			reject(w, 413, "context_too_large")
-			return nil
+			return rejectRequest(413, "context_too_large")
 		}
 
 		parameters, _ := step.Config["parameters"].(map[string]any)
 		if len(parameters) > 0 {
-			reject(w, 400, "invalid_ai_request")
-			return nil
+			return rejectRequest(400, "invalid_ai_request")
 		}
 		prompt, _ := step.Config["prompt"].(string)
 		text, _ := step.FrozenContent["text"].(string)
 		if len(prompt)+len(text) > model.MaxInputBytes {
-			reject(w, 413, "context_too_large")
-			return nil
+			return rejectRequest(413, "context_too_large")
 		}
 		var busy bool
-		err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND node_id=$4 AND status IN('queued','running'))`, project, workspace, step.BoardID, step.NodeID).Scan(&busy)
+		if step.CanonicalRoot != "" {
+			err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND frozen_input->>'canonical_root'=$3 AND node_id=$4 AND frozen_input->>'target_incarnation'=$5::bigint::text AND status IN('queued','running'))`, project, workspace, step.CanonicalRoot, step.NodeID, step.TargetIncarnation).Scan(&busy)
+		} else {
+			err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND node_id=$4 AND status IN('queued','running'))`, project, workspace, step.BoardID, step.NodeID).Scan(&busy)
+		}
 		if err != nil {
 			return err
 		}
 		if busy {
-			reject(w, 409, "node_busy")
-			return nil
+			return rejectRequest(409, "node_busy")
 		}
 	}
 	// A project-scoped advisory lock makes the queue limit atomic across workspaces.
@@ -276,8 +317,7 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	}
 	if queued >= 128 {
 		w.Header().Set("Retry-After", "5")
-		reject(w, 429, "queue_full")
-		return nil
+		return rejectRequest(429, "queue_full")
 	}
 	var id string
 	err = tx.QueryRowContext(r.Context(), `SELECT gen_random_uuid()::text`).Scan(&id)
@@ -287,12 +327,17 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	planJSON, _ := json.Marshal(plan)
 	poll := "/projects/" + url.PathEscape(project) + "/workspaces/" + workspace + "/materials/" + board + "/canvas/ai/runs/" + id
 	result := response{"run_id": id, "status": "queued", "poll_url": poll, "plan": publicAIPlan(plan), "canvas_version": parent.Version}
+	if root != "" {
+		result["protocol_version"], result["request_id"], result["admission"], result["operation_id"] = 2, key, "accepted", input.OperationID
+		change.addCanonical(result)
+	}
+	bindCanvasAIReceipt(result, receipt)
 	resultJSON, _ := json.Marshal(result)
-	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_ai_runs(project,workspace_id,board_id,id,account_id,idempotency_key,payload_hash,status,plan,create_response) VALUES($1,$2,$3,$4,$5,$6,$7,'queued',$8,$9)`, project, workspace, board, id, account, key, hash, planJSON, resultJSON)
+	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_ai_runs(project,workspace_id,board_id,id,account_id,idempotency_key,payload_hash,status,plan,create_response,logical_operation_id) VALUES($1,$2,$3,$4,$5,$6,$7,'queued',$8,$9,NULLIF($10,'')::uuid)`, project, workspace, board, id, account, key, hash, planJSON, resultJSON, input.OperationID)
 	if err != nil {
 		return err
 	}
-	if err = s.saveCanvas(r, tx, project, workspace, parent); err != nil {
+	if err = s.saveCanvasAIChange(r, tx, project, workspace, account, change); err != nil {
 		return err
 	}
 	if err = appendAIEvent(r.Context(), tx, project, workspace, id, "run.queued", response{"status": "queued"}); err != nil {
@@ -308,10 +353,6 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			return err
 		}
 	}
-	if err = tx.Commit(); err != nil {
-		return err
-	}
 	setVersion(w, parent.Version)
-	reply(w, 202, result)
-	return nil
+	return commitCanvasAIReceipt(w, r, tx, project, workspace, account, receipt, 202, "applied", result)
 }

internal/platform/canvas_capabilities.go

@@ -39,17 +39,18 @@ func (s *service) canvasCapabilities(w http.ResponseWriter, r *http.Request, pro
 			}
 		}
 	}
-	ai := response{"available": textAvailable || imageAvailable, "text": textAvailable, "image": imageAvailable}
+	ai := response{"canonical_target_identity": true, "owner_relocation": true, "admission_protocol_version": 2, "admission_receipt_query": true, "mutation_protocol_version": 2, "terminal_rejection_receipts": true, "available": textAvailable || imageAvailable, "text": textAvailable, "image": imageAvailable}
 	if modelErr != nil {
 		ai["unavailable_reason"] = "codex_unavailable"
 	}
 	reply(w, 200, response{
-		"contract_version":          "canvas-v2-2026-11-06",
+		"contract_version":          "canvas-headless-2026-11-07",
+		"canonical_model":           response{"document_format_version": canvasModelFormat, "protocol_version": canvasModelProtocol, "explicit_migration": true, "stable_element_ids": true, "atomic_multi_canvas": true, "logical_operation_dedup": true, "legacy_snapshot_writes": false},
 		"supported_schema_versions": []int{1, 2},
 		"edge_features":             response{"appearance": true, "markers": true, "bezier_chain": true, "animation_configuration": true, "execution_events": true},
 		"subgraphs":                 response{"create": true, "migrate": true, "undo": true, "members": true, "dissolve": true, "connections": true, "member_positions": true},
 		"ai":                        ai,
-		"assets":                    response{"previews": true, "preview_max_edge": 1024, "originals_preserved": true},
+		"assets":                    response{"client_resource_ids": true, "receipt_protocol_version": 2, "previews": true, "preview_max_edge": 1024, "originals_preserved": true},
 		"limits":                    response{"max_depth": 8, "max_nodes": 500, "max_edges": 2000, "max_frame_ports": 4000, "max_curve_knots": 64, "max_snapshot_bytes": canvasLimit, "max_active_tasks": 128, "max_run_steps": 64, "max_execution_depth": 32, "max_input_images": 4, "max_input_image_bytes": 20 << 20, "max_coordinate": 1000000},
 		"retention":                 response{"idempotency_min_seconds": 86400, "undo_receipt_seconds": 604800},
 	})

internal/platform/canvas_headless_client_integration_test.go

@@ -0,0 +1,83 @@
+package platform
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// Runs the real Endoleap runtime against authenticated Foundry HTTP and PostgreSQL.
+// This opt-in is enabled by the existing remote schema runner, never local builds.
+func TestHeadlessClientHTTPIntegration(t *testing.T) {
+	source, dsn := os.Getenv("FOUNDRY_HEADLESS_SOURCE"), os.Getenv("PLATFORM_TEST_DATABASE_URL")
+	if source == "" {
+		t.Skip("requires remote headless checkout")
+	}
+	if dsn == "" {
+		t.Fatal("headless integration requires isolated PostgreSQL")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	ctx := context.Background()
+	var entropy [12]byte
+	_, _ = rand.Read(entropy[:])
+	project := "headless-" + hex.EncodeToString(entropy[:])
+	defer func() {
+		for _, table := range []string{"canvas_ai_runs", "canvas_model_operations", "canvas_model_identity_map", "canvas_model_requests", "canvas_model_projects", "canvas_asset_bindings", "canvas_assets", "canvas_subgraphs", "workspaces", "project_accounts"} {
+			_, _ = db.ExecContext(ctx, "DELETE FROM "+table+" WHERE project=$1", project)
+		}
+	}()
+	var account, workspace, root string
+	if err = db.QueryRowContext(ctx, `INSERT INTO project_accounts(project,id) VALUES($1,gen_random_uuid()) RETURNING id::text`, project).Scan(&account); err != nil {
+		t.Fatal(err)
+	}
+	var tokenBytes [32]byte
+	_, _ = rand.Read(tokenBytes[:])
+	token := base64.RawURLEncoding.EncodeToString(tokenBytes[:])
+	hash := sha256.Sum256([]byte(token))
+	if _, err = db.ExecContext(ctx, `INSERT INTO project_sessions(token_hash,project,account_id,expires_at) VALUES($1,$2,$3,now()+interval '1 hour')`, base64.RawURLEncoding.EncodeToString(hash[:]), project, account); err != nil {
+		t.Fatal(err)
+	}
+	if err = db.QueryRowContext(ctx, `INSERT INTO workspaces(project,name,owner_id) VALUES($1,'Headless integration',$2) RETURNING id::text`, project, account).Scan(&workspace); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = db.ExecContext(ctx, `INSERT INTO workspace_members(project,workspace_id,account_id,role) VALUES($1,$2,$3,'admin')`, project, workspace, account); err != nil {
+		t.Fatal(err)
+	}
+	legacy := json.RawMessage(`{"schema_version":1,"nodes":[` + modelLegacyFrame + `,{"id":"a","type":"plainText","position":{"x":150,"y":260},"width":240,"height":72,"data":{"kind":"plain-text","title":"a","text":"preserved","frameId":"f"}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`)
+	if err = db.QueryRowContext(ctx, `INSERT INTO materials(project,workspace_id,kind,title,created_by,canvas_document) VALUES($1,$2,'board','Root',$3,$4) RETURNING id::text`, project, workspace, account, legacy).Scan(&root); err != nil {
+		t.Fatal(err)
+	}
+	mux := headlessWorkerRoutes(t, db, map[string]string{project: "https://app.example.com/auth/callback"}, project, account)
+
+	server := httptest.NewServer(mux)
+	defer server.Close()
+	commandContext, cancel := context.WithTimeout(ctx, 2*time.Minute)
+	defer cancel()
+	command := exec.CommandContext(commandContext, "node", filepath.Join(source, "tests/headless/foundry.integration.mjs"))
+	command.Env = append(os.Environ(), "FOUNDRY_HTTP_URL="+server.URL, "FOUNDRY_TEST_PROJECT="+project, "FOUNDRY_TEST_ACCOUNT="+account, "FOUNDRY_TEST_WORKSPACE="+workspace, "FOUNDRY_TEST_ROOT="+root, "FOUNDRY_TEST_TOKEN="+token, "FOUNDRY_TEST_AI_WORKER=1")
+	output, err := command.CombinedOutput()
+	// The fixture token is ephemeral, but never print it even on client failures.
+	report := strings.ReplaceAll(string(output), token, "[fixture token redacted]")
+	if err != nil {
+		t.Fatalf("headless HTTP client failed: %v\n%s", err, report)
+	}
+	if !strings.Contains(report, `"status":"ok"`) || !strings.Contains(report, `"runtimeAI":true`) {
+		t.Fatalf("headless HTTP client did not return success: %s", report)
+	}
+	t.Log(report)
+}

internal/platform/canvas_headless_worker_integration_test.go

@@ -0,0 +1,155 @@
+package platform
+
+import (
+	"bytes"
+	"database/sql"
+	"encoding/json"
+	"image"
+	"image/color"
+	"image/png"
+	"net"
+	"net/http"
+	"path/filepath"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+
+	"gitea.entroia.com/Zayden-Jung/foundry-core/internal/codex"
+)
+
+// Only the generation transport is deterministic. Admission, claims, events,
+// canonical writes and action receipts use the real service and isolated DB.
+func headlessWorkerRoutes(t *testing.T, db *sql.DB, callbacks map[string]string, project, account string) http.Handler {
+	t.Helper()
+	type gate struct {
+		entered, release  chan struct{}
+		started, released sync.Once
+	}
+	var mu sync.Mutex
+	var held *gate
+	var executions atomic.Int32
+	var picture bytes.Buffer
+	pixels := image.NewRGBA(image.Rect(0, 0, 3, 2))
+	pixels.Set(0, 0, color.RGBA{B: 255, A: 255})
+	if err := png.Encode(&picture, pixels); err != nil {
+		t.Fatal(err)
+	}
+	socket := filepath.Join(t.TempDir(), "worker.sock")
+	listener, err := net.Listen("unix", socket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	worker := &http.Server{Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/canvas/models" {
+			reply(w, 200, response{"models": []any{
+				codex.CanvasModel{ID: "fixture-text", Label: "Fixture text", Available: true, InputModalities: []string{"text", "image"}, OutputModalities: []string{"text"}, MaxInputBytes: 1 << 20, MaxExecutionMS: 90000},
+				codex.CanvasModel{ID: "fixture-image", Label: "Fixture image", Available: true, InputModalities: []string{"text", "image"}, OutputModalities: []string{"image"}, MaxInputBytes: 1 << 20, MaxExecutionMS: 90000},
+			}})
+			return
+		}
+		if r.URL.Path != "/canvas/exec" {
+			reject(w, 404, "not_found")
+			return
+		}
+		var task codex.CanvasTask
+		if json.NewDecoder(r.Body).Decode(&task) != nil {
+			reject(w, 400, "invalid_request")
+			return
+		}
+		executions.Add(1)
+		mu.Lock()
+		current := held
+		mu.Unlock()
+		if current != nil {
+			current.started.Do(func() { close(current.entered) })
+			select {
+			case <-current.release:
+			case <-r.Context().Done():
+				return
+			}
+			mu.Lock()
+			if held == current {
+				held = nil
+			}
+			mu.Unlock()
+		}
+		if task.OutputModality == "image" {
+			reply(w, 200, response{"output": codex.CanvasOutput{Kind: "image", Image: &codex.CanvasImage{MIME: "image/png", Data: picture.Bytes()}}})
+		} else {
+			reply(w, 200, response{"result": "headless fixture output"})
+		}
+	})}
+	go worker.Serve(listener)
+	t.Cleanup(func() {
+		mu.Lock()
+		if held != nil {
+			held.released.Do(func() { close(held.release) })
+		}
+		mu.Unlock()
+		worker.Close()
+	})
+	s := &service{db: db, origin: "https://api.example.com", canvasAI: codex.NewCanvasClient(socket)}
+	mux := http.NewServeMux()
+	prefix := "/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai"
+	mux.HandleFunc("GET "+prefix+"/models", s.protected(callbacks, s.canvasAIModels))
+	mux.HandleFunc("POST "+prefix+"/runs", s.protected(callbacks, s.createCanvasAIRun))
+	mux.HandleFunc("GET "+prefix+"/runs/{run}", s.protected(callbacks, s.getCanvasAIRun))
+	mux.HandleFunc("GET "+prefix+"/operations/{request}", s.protected(callbacks, s.getCanvasAIAdmission))
+	mux.HandleFunc("POST "+prefix+"/runs/{run}/cancel", s.protected(callbacks, s.cancelCanvasAIRun))
+	mux.HandleFunc("POST "+prefix+"/runs/{run}/apply", s.protected(callbacks, s.applyCanvasAIOutput))
+	// Private test controls are not registered by production Register().
+	mux.HandleFunc("POST "+prefix+"/fixture/{action}", s.protected(callbacks, func(w http.ResponseWriter, r *http.Request, p, a string) error {
+		if p != project || a != account {
+			reject(w, 403, "forbidden")
+			return nil
+		}
+		switch r.PathValue("action") {
+		case "arm":
+			mu.Lock()
+			held = &gate{entered: make(chan struct{}), release: make(chan struct{})}
+			mu.Unlock()
+		case "wait":
+			mu.Lock()
+			current := held
+			mu.Unlock()
+			if current == nil {
+				reject(w, 409, "worker_not_armed")
+				return nil
+			}
+			select {
+			case <-current.entered:
+			case <-r.Context().Done():
+				return nil
+			}
+		case "release":
+			mu.Lock()
+			if held != nil {
+				held.released.Do(func() { close(held.release) })
+			}
+			mu.Unlock()
+		case "execute":
+			run, err := s.claimCanvasRun(r.Context())
+			if err != nil || run == nil || run.Project != project || run.Account != account || run.Workspace != r.PathValue("workspace") {
+				reject(w, 409, "fixture_run_unavailable")
+				return nil
+			}
+			s.executeCanvasRun(r.Context(), *run)
+		case "stats":
+		default:
+			reject(w, 404, "not_found")
+			return nil
+		}
+		reply(w, 200, response{"executions": executions.Load()})
+		return nil
+	}))
+	regular := http.NewServeMux()
+	Register(regular, db, callbacks, "https://api.example.com", nil)
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if strings.Contains(r.URL.Path, "/canvas/ai/") {
+			mux.ServeHTTP(w, r)
+		} else {
+			regular.ServeHTTP(w, r)
+		}
+	})
+}

internal/platform/canvas_model.go

@@ -0,0 +1,450 @@
+package platform
+
+import (
+	"encoding/json"
+	"errors"
+	"math"
+	"reflect"
+	"sort"
+	"strings"
+)
+
+const canvasModelFormat = 1
+const canvasModelProtocol = 2
+
+var errCanvasModel = errors.New("invalid_canvas_model")
+var errModelConflict = errors.New("canvas_model_field_conflict")
+
+type modelParent struct {
+	CanvasID       string `json:"canvasId"`
+	EntryElementID string `json:"entryElementId"`
+}
+type modelCanvas struct {
+	ID     string       `json:"id"`
+	Parent *modelParent `json:"parent"`
+}
+type canvasModel struct {
+	Root            string
+	Canvases        map[string]modelCanvas
+	Elements        map[string]map[string]any
+	Tombstones      map[string]int64
+	TombstoneOwners map[string]string
+	DeadRecords     map[string]map[string]any
+	Versions        map[string]int64
+}
+type modelView struct {
+	Format     int              `json:"documentFormatVersion"`
+	ProjectID  string           `json:"projectId"`
+	Canvases   []modelCanvas    `json:"canvases"`
+	Elements   []map[string]any `json:"elements"`
+	Tombstones map[string]int64 `json:"tombstones"`
+	Versions   map[string]int64 `json:"versions"`
+	Complete   bool             `json:"complete"`
+	Removed    []string         `json:"removedCanvasIds"`
+}
+type modelTarget struct {
+	ID          string `json:"id"`
+	Incarnation int64  `json:"incarnation"`
+}
+type modelChange struct {
+	Kind          string          `json:"kind"`
+	ID            string          `json:"id,omitempty"`
+	Target        modelTarget     `json:"target,omitempty"`
+	Field         string          `json:"field,omitempty"`
+	Before        json.RawMessage `json:"before"`
+	After         json.RawMessage `json:"after"`
+	BeforePresent *bool           `json:"beforePresent,omitempty"`
+	AfterPresent  *bool           `json:"afterPresent,omitempty"`
+}
+type modelOperation struct {
+	ID      string        `json:"id"`
+	Changes []modelChange `json:"changes"`
+}
+type modelBatch struct {
+	ProtocolVersion int              `json:"protocol_version"`
+	RequestID       string           `json:"request_id"`
+	Expected        map[string]int64 `json:"expected_versions"`
+	Operations      []modelOperation `json:"operations"`
+}
+
+func emptyModel(root string) canvasModel {
+	return canvasModel{Root: root, Canvases: map[string]modelCanvas{}, Elements: map[string]map[string]any{}, Tombstones: map[string]int64{}, TombstoneOwners: map[string]string{}, DeadRecords: map[string]map[string]any{}, Versions: map[string]int64{}}
+}
+func modelString(value any) string { text, _ := value.(string); return text }
+func modelInt(value any) int64 {
+	number, ok := value.(float64)
+	if !ok || number < 1 || number > 9007199254740991 || math.Trunc(number) != number {
+		return 0
+	}
+	return int64(number)
+}
+func modelJSONSafe(value any, depth int) bool {
+	if depth > 64 {
+		return false
+	}
+	switch value := value.(type) {
+	case nil, bool, string:
+		return true
+	case float64:
+		return !math.IsNaN(value) && !math.IsInf(value, 0)
+	case []any:
+		for _, item := range value {
+			if !modelJSONSafe(item, depth+1) {
+				return false
+			}
+		}
+		return true
+	case map[string]any:
+		for _, item := range value {
+			if !modelJSONSafe(item, depth+1) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}
+func modelEqual(left, right any) bool {
+	// Round-trip numeric Go structs and JSON records to the same JSON value domain.
+	a, ea := json.Marshal(left)
+	b, eb := json.Marshal(right)
+	if ea != nil || eb != nil {
+		return false
+	}
+	var av, bv any
+	return json.Unmarshal(a, &av) == nil && json.Unmarshal(b, &bv) == nil && reflect.DeepEqual(av, bv)
+}
+func (model canvasModel) view(participants map[string]int64) modelView {
+	view := modelView{Format: canvasModelFormat, ProjectID: model.Root, Canvases: []modelCanvas{}, Elements: []map[string]any{}, Tombstones: map[string]int64{}, Versions: map[string]int64{}, Complete: participants == nil, Removed: []string{}}
+	for _, id := range sortedKeys(model.Canvases) {
+		if participants != nil {
+			if _, exists := participants[id]; !exists {
+				continue
+			}
+		}
+		view.Canvases = append(view.Canvases, model.Canvases[id])
+		view.Versions[id] = model.Versions[id]
+	}
+	for _, id := range sortedKeys(model.Elements) {
+		element := model.Elements[id]
+		if participants != nil {
+			if _, exists := participants[modelString(element["ownerCanvasId"])]; !exists {
+				continue
+			}
+		}
+		view.Elements = append(view.Elements, element)
+	}
+	for id, incarnation := range model.Tombstones {
+		owner := model.TombstoneOwners[id]
+		if live := model.Elements[id]; live != nil {
+			owner = modelString(live["ownerCanvasId"])
+		}
+		if participants != nil {
+			if _, exists := participants[owner]; !exists {
+				continue
+			}
+		}
+		view.Tombstones[id] = incarnation
+	}
+	for _, id := range sortedKeys(model.Versions) {
+		if participants != nil {
+			if _, exists := participants[id]; !exists {
+				continue
+			}
+		}
+		view.Versions[id] = model.Versions[id]
+		if _, exists := model.Canvases[id]; !exists {
+			view.Removed = append(view.Removed, id)
+		}
+	}
+	return view
+}
+func sortedKeys[T any](values map[string]T) []string {
+	keys := make([]string, 0, len(values))
+	for key := range values {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	return keys
+}
+func cloneModel(model canvasModel) canvasModel {
+	raw, _ := json.Marshal(model)
+	var copy canvasModel
+	_ = json.Unmarshal(raw, &copy)
+	return copy
+}
+func modelAncestors(model canvasModel, id string) ([]string, error) {
+	path, seen := []string{}, map[string]bool{}
+	for id != "" {
+		canvas, exists := model.Canvases[id]
+		if !exists || seen[id] || len(path) > 8 {
+			return nil, errCanvasModel
+		}
+		seen[id] = true
+		path = append(path, id)
+		id = ""
+		if canvas.Parent != nil {
+			id = canvas.Parent.CanvasID
+		}
+	}
+	return path, nil
+}
+func modelCommonCanvas(model canvasModel, left, right string) (string, error) {
+	a, err := modelAncestors(model, left)
+	if err != nil {
+		return "", err
+	}
+	b, err := modelAncestors(model, right)
+	if err != nil {
+		return "", err
+	}
+	seen := map[string]bool{}
+	for _, id := range a {
+		seen[id] = true
+	}
+	for _, id := range b {
+		if seen[id] {
+			return id, nil
+		}
+	}
+	return "", errCanvasModel
+}
+func validateCanvasModel(model canvasModel) error {
+	if !uuidSlugPattern.MatchString(model.Root) || len(model.Canvases) == 0 || len(model.Canvases) > 256 || len(model.Elements) > 128000 {
+		return errCanvasModel
+	}
+	roots, entries, counts := 0, map[string]bool{}, map[string][2]int{}
+	for id, canvas := range model.Canvases {
+		if id != canvas.ID || !uuidSlugPattern.MatchString(id) {
+			return errCanvasModel
+		}
+		if _, err := modelAncestors(model, id); err != nil {
+			return err
+		}
+		if canvas.Parent == nil {
+			roots++
+			if id != model.Root {
+				return errCanvasModel
+			}
+			continue
+		}
+		entry := model.Elements[canvas.Parent.EntryElementID]
+		if entry == nil || entry["structure"] != "node" || entry["ownerCanvasId"] != canvas.Parent.CanvasID || entries[canvas.Parent.EntryElementID] {
+			return errCanvasModel
+		}
+		entries[canvas.Parent.EntryElementID] = true
+	}
+	if roots != 1 {
+		return errCanvasModel
+	}
+	for id, incarnation := range model.Tombstones {
+		if !canvasID.MatchString(id) || incarnation < 1 || incarnation > 9007199254740991 {
+			return errCanvasModel
+		}
+	}
+	for id, element := range model.Elements {
+		if !modelJSONSafe(element, 0) {
+			return errCanvasModel
+		}
+		owner, component := modelString(element["ownerCanvasId"]), modelString(element["componentId"])
+		_, canvasExists := model.Canvases[owner]
+		incarnation, version := modelInt(element["incarnation"]), modelInt(element["dataVersion"])
+		data, dataOK := element["data"].(map[string]any)
+		if !canvasID.MatchString(id) || element["id"] != id || !canvasExists || incarnation == 0 || incarnation <= model.Tombstones[id] || version == 0 || component == "" || len(component) > 128 || !dataOK || data == nil {
+			return errCanvasModel
+		}
+		encoded, err := json.Marshal(element)
+		if err != nil || len(encoded) > 1<<20 {
+			return errCanvasModel
+		}
+		count := counts[owner]
+		switch element["structure"] {
+		case "node":
+			count[0]++
+			geometry, ok := element["geometry"].(map[string]any)
+			if !ok || !canvasNumber(geometry["x"], -1e6, 1e6) || !canvasNumber(geometry["y"], -1e6, 1e6) || !canvasNumber(geometry["width"], 0.000001, 1e6) || !canvasNumber(geometry["height"], 0.000001, 1e6) || !canvasNumber(geometry["rotation"], 0, math.Nextafter(360, 0)) {
+				return errCanvasModel
+			}
+			if version == 1 && canvasChoice(component, "text", "image", "script", "plain-text", "plain-image", "icon", "frame") {
+				// Canonical frames can inherit rotation while changing owners. The
+				// legacy snapshot writer's zero-angle restriction does not apply here.
+				if !canvasString(data["title"], 300) || !canvasString(data["text"], 100000) {
+					return errCanvasModel
+				}
+				if ai, exists := data["ai"]; exists && !validCanvasAI(ai, component) {
+					return errCanvasModel
+				}
+				if asset, exists := data["assetId"]; exists && (!canvasChoice(component, "image", "plain-image") || !uuidSlugPattern.MatchString(modelString(asset))) {
+					return errCanvasModel
+				}
+			}
+		case "connection":
+			count[1]++
+			source, sourceOK := element["source"].(map[string]any)
+			target, targetOK := element["target"].(map[string]any)
+			if !sourceOK || !targetOK {
+				return errCanvasModel
+			}
+			a, b := model.Elements[modelString(source["elementId"])], model.Elements[modelString(target["elementId"])]
+			if a == nil || b == nil || a["structure"] != "node" || b["structure"] != "node" {
+				return errCanvasModel
+			}
+			for _, endpoint := range []map[string]any{source, target} {
+				if port, exists := endpoint["portId"]; exists && (!canvasString(port, 256) || modelString(port) == "") {
+					return errCanvasModel
+				}
+			}
+			common, err := modelCommonCanvas(model, modelString(a["ownerCanvasId"]), modelString(b["ownerCanvasId"]))
+			if err != nil || common != owner {
+				return errCanvasModel
+			}
+		default:
+			return errCanvasModel
+		}
+		if count[0] > 500 || count[1] > 2000 {
+			return errGraphCapacity
+		}
+		counts[owner] = count
+	}
+	return nil
+}
+
+// Pure transaction reducer. Unknown component data/envelope fields are retained.
+func applyModelOperations(initial canvasModel, operations []modelOperation) (canvasModel, map[string]bool, error) {
+	model, touched, seen := cloneModel(initial), map[string]bool{}, map[string]bool{}
+	if len(operations) == 0 || len(operations) > 2500 {
+		return model, nil, errCanvasModel
+	}
+	changeCount := 0
+	for _, operation := range operations {
+		if !uuidSlugPattern.MatchString(operation.ID) || seen[operation.ID] || len(operation.Changes) == 0 {
+			return model, nil, errCanvasModel
+		}
+		seen[operation.ID] = true
+		for _, change := range operation.Changes {
+			changeCount++
+			if changeCount > 10000 {
+				return model, nil, errGraphCapacity
+			}
+			var before, after any
+			if json.Unmarshal(change.Before, &before) != nil || json.Unmarshal(change.After, &after) != nil {
+				return model, nil, errCanvasModel
+			}
+			switch change.Kind {
+			case "field":
+				element := model.Elements[change.Target.ID]
+				if element == nil || modelInt(element["incarnation"]) != change.Target.Incarnation {
+					return model, nil, errModelConflict
+				}
+				touched[modelString(element["ownerCanvasId"])] = true
+				if strings.HasPrefix(change.Field, "data.") {
+					key := strings.TrimPrefix(change.Field, "data.")
+					if key == "" || canvasChoice(key, "__proto__", "constructor", "prototype") {
+						return model, nil, errCanvasModel
+					}
+					data := element["data"].(map[string]any)
+					prior, present := data[key]
+					if present != (change.BeforePresent == nil || *change.BeforePresent) || !modelEqual(prior, before) {
+						return model, nil, errModelConflict
+					}
+					if change.AfterPresent != nil && !*change.AfterPresent {
+						delete(data, key)
+					} else {
+						data[key] = after
+					}
+				} else {
+					if !canvasChoice(change.Field, "geometry", "ownerCanvasId", "source", "target", "path") {
+						return model, nil, errCanvasModel
+					}
+					if !modelEqual(element[change.Field], before) {
+						return model, nil, errModelConflict
+					}
+					element[change.Field] = after
+					if change.Field == "ownerCanvasId" {
+						touched[modelString(after)] = true
+					}
+				}
+			case "element":
+				if !canvasID.MatchString(change.ID) || !modelEqual(model.Elements[change.ID], before) {
+					return model, nil, errModelConflict
+				}
+				if prior := model.Elements[change.ID]; prior != nil {
+					touched[modelString(prior["ownerCanvasId"])] = true
+				}
+				if after == nil {
+					if prior := model.Elements[change.ID]; prior != nil {
+						model.Tombstones[change.ID] = modelInt(prior["incarnation"])
+						model.TombstoneOwners[change.ID] = modelString(prior["ownerCanvasId"])
+						model.DeadRecords[change.ID] = prior
+					}
+					delete(model.Elements, change.ID)
+				} else {
+					record, ok := after.(map[string]any)
+					if !ok || record["id"] != change.ID {
+						return model, nil, errCanvasModel
+					}
+					if before == nil && modelInt(record["incarnation"]) <= model.Tombstones[change.ID] {
+						return model, nil, errModelConflict
+					}
+					if prior := model.Elements[change.ID]; prior != nil && modelInt(record["incarnation"]) != modelInt(prior["incarnation"]) {
+						return model, nil, errModelConflict
+					}
+					model.Elements[change.ID] = record
+					touched[modelString(record["ownerCanvasId"])] = true
+				}
+			case "canvas":
+				prior, exists := model.Canvases[change.ID]
+				var priorValue any
+				if exists {
+					priorValue = prior
+				}
+				if !uuidSlugPattern.MatchString(change.ID) || !modelEqual(priorValue, before) {
+					return model, nil, errModelConflict
+				}
+				touched[change.ID] = true
+				if prior.Parent != nil {
+					touched[prior.Parent.CanvasID] = true
+				}
+				if after == nil {
+					delete(model.Canvases, change.ID)
+				} else {
+					var canvas modelCanvas
+					if json.Unmarshal(change.After, &canvas) != nil || canvas.ID != change.ID {
+						return model, nil, errCanvasModel
+					}
+					model.Canvases[change.ID] = canvas
+					if canvas.Parent != nil {
+						touched[canvas.Parent.CanvasID] = true
+					}
+				}
+			default:
+				return model, nil, errCanvasModel
+			}
+		}
+	}
+	if err := validateCanvasModel(model); err != nil {
+		return model, nil, err
+	}
+	// Endpoint owners are read participants, guarding against delete/restore races in child canvases.
+	for _, operation := range operations {
+		for _, change := range operation.Changes {
+			if change.Kind == "element" && string(change.Before) == "null" || change.Kind == "field" && (change.Field == "source" || change.Field == "target") {
+				id := change.ID
+				if change.Kind == "field" {
+					id = change.Target.ID
+				}
+				element := model.Elements[id]
+				if element != nil && element["structure"] == "connection" {
+					for _, field := range []string{"source", "target"} {
+						endpoint := element[field].(map[string]any)
+						touched[modelString(model.Elements[modelString(endpoint["elementId"])]["ownerCanvasId"])] = true
+					}
+				}
+			}
+		}
+	}
+	for id := range touched {
+		model.Versions[id] = initial.Versions[id] + 1
+	}
+	return model, touched, nil
+}

internal/platform/canvas_model_atomic_integration_test.go

@@ -0,0 +1,389 @@
+package platform
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+	"time"
+)
+
+type canonicalAtomicFixture struct {
+	db                                       *sql.DB
+	mux                                      *http.ServeMux
+	project, account, workspace, root, token string
+	legacy                                   json.RawMessage
+}
+
+func newCanonicalAtomicFixture(t *testing.T) *canonicalAtomicFixture {
+	t.Helper()
+	dsn := os.Getenv("PLATFORM_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("requires an isolated integration database")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { db.Close() })
+	var entropy [12]byte
+	_, _ = rand.Read(entropy[:])
+	f := &canonicalAtomicFixture{db: db, project: "canonical-atomic-" + hex.EncodeToString(entropy[:])}
+	ctx := context.Background()
+	t.Cleanup(func() {
+		for _, table := range []string{"canvas_ai_runs", "canvas_model_operations", "canvas_model_identity_map", "canvas_model_requests", "canvas_model_projects", "canvas_asset_bindings", "canvas_subgraphs", "workspaces", "project_accounts"} {
+			_, _ = db.ExecContext(ctx, "DELETE FROM "+table+" WHERE project=$1", f.project)
+		}
+	})
+	if err = db.QueryRowContext(ctx, `INSERT INTO project_accounts(project,id) VALUES($1,gen_random_uuid()) RETURNING id::text`, f.project).Scan(&f.account); err != nil {
+		t.Fatal(err)
+	}
+	var tokenBytes [32]byte
+	_, _ = rand.Read(tokenBytes[:])
+	f.token = base64.RawURLEncoding.EncodeToString(tokenBytes[:])
+	hash := sha256.Sum256([]byte(f.token))
+	if _, err = db.ExecContext(ctx, `INSERT INTO project_sessions(token_hash,project,account_id,expires_at) VALUES($1,$2,$3,now()+interval '1 hour')`, base64.RawURLEncoding.EncodeToString(hash[:]), f.project, f.account); err != nil {
+		t.Fatal(err)
+	}
+	if err = db.QueryRowContext(ctx, `INSERT INTO workspaces(project,name,owner_id) VALUES($1,'Canonical atomic',$2) RETURNING id::text`, f.project, f.account).Scan(&f.workspace); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = db.ExecContext(ctx, `INSERT INTO workspace_members(project,workspace_id,account_id,role) VALUES($1,$2,$3,'admin')`, f.project, f.workspace, f.account); err != nil {
+		t.Fatal(err)
+	}
+	f.legacy = json.RawMessage(`{"schema_version":1,"nodes":[` + modelLegacyFrame + `,{"id":"a","type":"material","position":{"x":150,"y":260},"width":240,"height":72,"data":{"kind":"text","title":"a","text":"preserved","frameId":"f"}},{"id":"b","type":"material","position":{"x":180,"y":300},"width":240,"height":72,"data":{"kind":"text","title":"b","text":"preserved","frameId":"f"}},{"id":"c","type":"material","position":{"x":0,"y":0},"width":240,"height":72,"data":{"kind":"text","title":"c","text":"unrelated"}}],"edges":[{"id":"e","source":"a","target":"b"}],"viewport":{"x":0,"y":0,"zoom":1}}`)
+	if err = db.QueryRowContext(ctx, `INSERT INTO materials(project,workspace_id,kind,title,created_by,canvas_document) VALUES($1,$2,'board','Root',$3,$4) RETURNING id::text`, f.project, f.workspace, f.account, f.legacy).Scan(&f.root); err != nil {
+		t.Fatal(err)
+	}
+	f.mux = http.NewServeMux()
+	Register(f.mux, db, map[string]string{f.project: "https://app.example.com/auth/callback"}, "https://api.example.com", nil)
+	return f
+}
+
+func (f *canonicalAtomicFixture) path() string {
+	return "/projects/" + f.project + "/workspaces/" + f.workspace + "/materials/" + f.root + "/canvas/model"
+}
+
+func (f *canonicalAtomicFixture) request(ctx context.Context, method, path, key string, raw []byte) *httptest.ResponseRecorder {
+	r := httptest.NewRequest(method, path, bytes.NewReader(raw)).WithContext(ctx)
+	r.Header.Set("Authorization", "Bearer "+f.token)
+	r.Header.Set("X-Expected-Account", f.account)
+	r.Header.Set("Accept", "application/vnd.foundry.canvas+json;version=2")
+	if key != "" {
+		r.Header.Set("Idempotency-Key", key)
+	}
+	w := httptest.NewRecorder()
+	f.mux.ServeHTTP(w, r)
+	return w
+}
+
+func canonicalAtomicResponse(t *testing.T, w *httptest.ResponseRecorder, status int) response {
+	t.Helper()
+	if w.Code != status {
+		t.Fatalf("canonical response got %d %s want %d", w.Code, w.Body.String(), status)
+	}
+	var body response
+	if err := json.Unmarshal(w.Body.Bytes(), &body); err != nil {
+		t.Fatal(err)
+	}
+	return body
+}
+
+func (f *canonicalAtomicFixture) read(t *testing.T) canvasModel {
+	t.Helper()
+	tx, err := f.db.BeginTx(context.Background(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer tx.Rollback()
+	model, err := loadCanvasModel(context.Background(), tx, f.project, f.workspace, f.root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return model
+}
+
+func (f *canonicalAtomicFixture) concurrent(t *testing.T, path string, keys []string, bodies [][]byte) []*httptest.ResponseRecorder {
+	t.Helper()
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	defer cancel()
+	type result struct {
+		index  int
+		writer *httptest.ResponseRecorder
+	}
+	start, done := make(chan struct{}), make(chan result, len(keys))
+	for i := range keys {
+		go func(index int) {
+			<-start
+			done <- result{index, f.request(ctx, "POST", path, keys[index], bodies[index])}
+		}(i)
+	}
+	close(start)
+	out := make([]*httptest.ResponseRecorder, len(keys))
+	for range keys {
+		select {
+		case value := <-done:
+			out[value.index] = value.writer
+		case <-ctx.Done():
+			t.Fatal("canonical concurrent requests did not finish")
+		}
+	}
+	return out
+}
+
+func TestCanonicalConcurrentMigrationAndOwnershipWrites(t *testing.T) {
+	f := newCanonicalAtomicFixture(t)
+	ctx := context.Background()
+	key := modelTestID(8000)
+	input := response{"protocol_version": 2, "request_id": key, "expected_versions": map[string]int64{f.root: 1}}
+	raw := modelJSON(input)
+	replies := f.concurrent(t, f.path()+"/migrate", []string{key, key, key, key}, [][]byte{raw, raw, raw, raw})
+	first := canonicalAtomicResponse(t, replies[0], 200)
+	for _, reply := range replies[1:] {
+		if !modelEqual(first, canonicalAtomicResponse(t, reply, 200)) {
+			t.Fatal("concurrent migration allocated different identities or receipts")
+		}
+	}
+	ids := map[string]string{}
+	for _, value := range first["identity_map"].([]any) {
+		mapping := value.(map[string]any)
+		ids[mapping["sourceId"].(string)] = mapping["elementId"].(string)
+	}
+	before := f.read(t)
+	child := modelString(before.Elements[ids["a"]]["ownerCanvasId"])
+	if len(before.Canvases) != 2 || len(ids) != 5 || child == f.root || before.Versions[f.root] != 2 || before.Versions[child] != 1 {
+		t.Fatal("concurrent migration duplicated the implicit partition or version barrier")
+	}
+	key = modelTestID(8001)
+	edit := modelBatch{ProtocolVersion: 2, RequestID: key, Expected: map[string]int64{child: 1}, Operations: []modelOperation{{ID: modelTestID(8002), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: ids["a"], Incarnation: 1}, Field: "data.title", Before: modelJSON("a"), After: modelJSON("renamed")}}}}}
+	raw = modelJSON(edit)
+	replies = f.concurrent(t, f.path()+"/operations", []string{key, key, key, key}, [][]byte{raw, raw, raw, raw})
+	first = canonicalAtomicResponse(t, replies[0], 200)
+	for _, reply := range replies[1:] {
+		if !modelEqual(first, canonicalAtomicResponse(t, reply, 200)) {
+			t.Fatal("concurrent edit retry changed its original receipt")
+		}
+	}
+	before = f.read(t)
+	if before.Versions[child] != 2 || before.Versions[f.root] != 2 || modelString(before.Elements[ids["a"]]["data"].(map[string]any)["title"]) != "renamed" {
+		t.Fatal("concurrent edit executed more than once")
+	}
+	var batches []modelBatch
+	var keys []string
+	var bodies [][]byte
+	for index, node := range []string{ids["a"], ids["b"]} {
+		key := modelTestID(8100 + index)
+		batch := modelBatch{ProtocolVersion: 2, RequestID: key, Expected: map[string]int64{f.root: 2, child: 2}, Operations: []modelOperation{{ID: modelTestID(8200 + index), Changes: []modelChange{
+			{Kind: "field", Target: modelTarget{ID: node, Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(child), After: modelJSON(f.root)},
+			{Kind: "field", Target: modelTarget{ID: ids["e"], Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(child), After: modelJSON(f.root)},
+		}}}}
+		batches, keys, bodies = append(batches, batch), append(keys, key), append(bodies, modelJSON(batch))
+	}
+	replies = f.concurrent(t, f.path()+"/operations", keys, bodies)
+	winner, successes := -1, 0
+	for index, reply := range replies {
+		status := 412
+		if reply.Code == 200 {
+			winner, successes, status = index, successes+1, 200
+		}
+		body := canonicalAtomicResponse(t, reply, status)
+		queried := canonicalAtomicResponse(t, f.request(ctx, "GET", f.path()+"/operations/"+keys[index], "", nil), 200)
+		if !modelEqual(body, queried) || status == 412 && (body["status"] != "not-applied" || body["terminal"] != true || body["error"] != "version_conflict") {
+			t.Fatal("a competing write lost its queryable applied or zero-effect receipt")
+		}
+	}
+	if successes != 1 {
+		t.Fatal("competing conditional ownership writes did not have exactly one winner")
+	}
+	after := f.read(t)
+	if err := validateCanvasModel(after); err != nil {
+		t.Fatal(err)
+	}
+	nodes := []string{ids["a"], ids["b"]}
+	if after.Versions[f.root] != 3 || after.Versions[child] != 3 || modelString(after.Elements[nodes[winner]]["ownerCanvasId"]) != f.root || modelString(after.Elements[nodes[1-winner]]["ownerCanvasId"]) != child || modelString(after.Elements[ids["e"]]["ownerCanvasId"]) != f.root || !modelEqual(before.Elements[ids["c"]], after.Elements[ids["c"]]) || !modelEqual(before.Canvases, after.Canvases) {
+		t.Fatal("competing ownership writes published a partial node/edge/tree or advanced versions twice")
+	}
+	var count int
+	if err := f.db.QueryRowContext(ctx, `SELECT count(*) FROM canvas_model_operations WHERE project=$1`, f.project).Scan(&count); err != nil || count != 2 {
+		t.Fatalf("logical operations: %d %v", count, err)
+	}
+	changed := batches[winner]
+	changed.Operations[0].ID = modelTestID(8999)
+	body := canonicalAtomicResponse(t, f.request(ctx, "POST", f.path()+"/operations", keys[winner], modelJSON(changed)), 409)
+	if body["error"] != "idempotency_conflict" || !modelEqual(after, f.read(t)) {
+		t.Fatal("same key with different bytes changed the canonical model")
+	}
+}
+
+func TestCanonicalMigrationLateCancellationRollsBack(t *testing.T) {
+	f := newCanonicalAtomicFixture(t)
+	ctx, stop := context.WithTimeout(context.Background(), 20*time.Second)
+	defer stop()
+	barrier, err := f.db.BeginTx(ctx, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer barrier.Rollback()
+	if _, err = barrier.ExecContext(ctx, `LOCK TABLE canvas_model_identity_map IN ACCESS EXCLUSIVE MODE`); err != nil {
+		t.Fatal(err)
+	}
+	var blocker int
+	if err = barrier.QueryRowContext(ctx, `SELECT pg_backend_pid()`).Scan(&blocker); err != nil {
+		t.Fatal(err)
+	}
+	key := modelTestID(8300)
+	input := response{"protocol_version": 2, "request_id": key, "expected_versions": map[string]int64{f.root: 1}}
+	requestContext, cancel := context.WithCancel(ctx)
+	defer cancel()
+	done := make(chan *httptest.ResponseRecorder, 1)
+	go func() { done <- f.request(requestContext, "POST", f.path()+"/migrate", key, modelJSON(input)) }()
+	// Observe the actual late INSERT blocked behind this transaction. A timer
+	// alone cannot prove migration reached canonical/material/subgraph writes.
+	ticker := time.NewTicker(10 * time.Millisecond)
+	defer ticker.Stop()
+	observed := false
+	for !observed {
+		if err = f.db.QueryRowContext(ctx, `SELECT EXISTS(SELECT 1 FROM pg_stat_activity WHERE usename=current_user AND query LIKE 'INSERT INTO canvas_model_identity_map%' AND $1=ANY(pg_blocking_pids(pid)))`, blocker).Scan(&observed); err != nil {
+			t.Fatal(err)
+		}
+		if observed {
+			break
+		}
+		select {
+		case reply := <-done:
+			t.Fatalf("migration did not reach its late write: %d %s", reply.Code, reply.Body.String())
+		case <-ctx.Done():
+			t.Fatal("migration never reached its late identity-map INSERT")
+		case <-ticker.C:
+		}
+	}
+	cancel()
+	select {
+	case reply := <-done:
+		canonicalAtomicResponse(t, reply, 503)
+	case <-ctx.Done():
+		t.Fatal("cancelled migration did not finish")
+	}
+	if err = barrier.Rollback(); err != nil {
+		t.Fatal(err)
+	}
+	for _, table := range []string{"canvas_model_projects", "canvas_model_canvases", "canvas_model_elements", "canvas_model_identity_map", "canvas_model_requests", "canvas_model_operations", "canvas_subgraphs"} {
+		var count int
+		if err = f.db.QueryRowContext(ctx, "SELECT count(*) FROM "+table+" WHERE project=$1", f.project).Scan(&count); err != nil || count != 0 {
+			t.Fatalf("late cancellation left %s rows: %d %v", table, count, err)
+		}
+	}
+	var count int
+	var version int64
+	var source json.RawMessage
+	if err = f.db.QueryRowContext(ctx, `SELECT count(*) FROM materials WHERE project=$1`, f.project).Scan(&count); err != nil || count != 1 {
+		t.Fatalf("synthetic partition material survived rollback: %d %v", count, err)
+	}
+	if err = f.db.QueryRowContext(ctx, `SELECT canvas_version,canvas_document FROM materials WHERE project=$1 AND id=$2`, f.project, f.root).Scan(&version, &source); err != nil || version != 1 || !modelEqual(f.legacy, source) {
+		t.Fatalf("late cancellation changed legacy source/version: %d %v", version, err)
+	}
+	// Infrastructure failure saved no result. The same original request can be
+	// retried safely, and all subsequent retries must return its one identity map.
+	first := canonicalAtomicResponse(t, f.request(ctx, "POST", f.path()+"/migrate", key, modelJSON(input)), 200)
+	retry := canonicalAtomicResponse(t, f.request(ctx, "POST", f.path()+"/migrate", key, modelJSON(input)), 200)
+	if !modelEqual(first, retry) || len(f.read(t).Canvases) != 2 {
+		t.Fatal("retry after rollback duplicated identities or the implicit partition")
+	}
+}
+
+func TestCanonicalMigrationPermissionVersionAndRunGuards(t *testing.T) {
+	f := newCanonicalAtomicFixture(t)
+	ctx := context.Background()
+	input := func(key string, version int64) response {
+		return response{"protocol_version": 2, "request_id": key, "expected_versions": map[string]int64{f.root: version}}
+	}
+	call := func(key string, version int64, status int) response {
+		t.Helper()
+		return canonicalAtomicResponse(t, f.request(ctx, "POST", f.path()+"/migrate", key, modelJSON(input(key, version))), status)
+	}
+	assertLegacy := func(version int64) {
+		t.Helper()
+		for _, table := range []string{"canvas_model_projects", "canvas_model_canvases", "canvas_model_elements", "canvas_model_identity_map", "canvas_subgraphs"} {
+			var count int
+			if err := f.db.QueryRowContext(ctx, "SELECT count(*) FROM "+table+" WHERE project=$1", f.project).Scan(&count); err != nil || count != 0 {
+				t.Fatalf("rejected migration left %s rows: %d %v", table, count, err)
+			}
+		}
+		var count int
+		var current int64
+		var source json.RawMessage
+		if err := f.db.QueryRowContext(ctx, `SELECT count(*) FROM materials WHERE project=$1`, f.project).Scan(&count); err != nil || count != 1 {
+			t.Fatalf("rejected migration created a material: %d %v", count, err)
+		}
+		if err := f.db.QueryRowContext(ctx, `SELECT canvas_version,canvas_document FROM materials WHERE project=$1 AND id=$2`, f.project, f.root).Scan(&current, &source); err != nil || current != version || !modelEqual(f.legacy, source) {
+			t.Fatalf("rejected migration changed legacy source/version: %d %v", current, err)
+		}
+	}
+	if _, err := f.db.ExecContext(ctx, `UPDATE workspace_members SET role='viewer' WHERE project=$1 AND workspace_id=$2 AND account_id=$3`, f.project, f.workspace, f.account); err != nil {
+		t.Fatal(err)
+	}
+	if call(modelTestID(8500), 1, 403)["error"] != "forbidden" {
+		t.Fatal("viewer crossed the identity migration barrier")
+	}
+	assertLegacy(1)
+	if _, err := f.db.ExecContext(ctx, `UPDATE workspace_members SET role='admin' WHERE project=$1 AND workspace_id=$2 AND account_id=$3`, f.project, f.workspace, f.account); err != nil {
+		t.Fatal(err)
+	}
+	staleKey := modelTestID(8501)
+	rejected := call(staleKey, 2, 412)
+	if rejected["status"] != "not-applied" || rejected["terminal"] != true || rejected["error"] != "migration_version_conflict" {
+		t.Fatal("stale source migration did not produce a zero-effect receipt")
+	}
+	assertLegacy(1)
+	// Advance the old writer to the formerly rejected expected version. That
+	// cannot turn the same frozen negative request into a migration later.
+	if _, err := f.db.ExecContext(ctx, `UPDATE materials SET canvas_version=2 WHERE project=$1 AND id=$2`, f.project, f.root); err != nil {
+		t.Fatal(err)
+	}
+	if !modelEqual(rejected, call(staleKey, 2, 412)) {
+		t.Fatal("a source version change reevaluated a rejected migration key")
+	}
+	assertLegacy(2)
+	run := modelTestID(8400)
+	if _, err := f.db.ExecContext(ctx, `INSERT INTO canvas_ai_runs(project,workspace_id,board_id,id,account_id,idempotency_key,payload_hash,status,plan,create_response) VALUES($1,$2,$3,$4,$5,$6,'fixture','queued','{}','{}')`, f.project, f.workspace, f.root, run, f.account, modelTestID(8401)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.db.ExecContext(ctx, `INSERT INTO canvas_ai_steps(project,workspace_id,run_id,id,board_id,node_id,ordinal,status,model_id,frozen_input,target_fingerprint) VALUES($1,$2,$3,'fixture',$4,'a',0,'queued','fixture','{}','fixture')`, f.project, f.workspace, run, f.root); err != nil {
+		t.Fatal(err)
+	}
+	for index, status := range []string{"queued", "running"} {
+		if _, err := f.db.ExecContext(ctx, `UPDATE canvas_ai_runs SET status=$4 WHERE project=$1 AND workspace_id=$2 AND id=$3`, f.project, f.workspace, run, status); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := f.db.ExecContext(ctx, `UPDATE canvas_ai_steps SET status=$4 WHERE project=$1 AND workspace_id=$2 AND run_id=$3`, f.project, f.workspace, run, status); err != nil {
+			t.Fatal(err)
+		}
+		body := call(modelTestID(8600+index), 2, 409)
+		if body["status"] != "not-applied" || body["terminal"] != true || body["error"] != "migration_waiting_for_runs" {
+			t.Fatal("identity migration crossed queued or outcome-unknown execution")
+		}
+		assertLegacy(2)
+	}
+	if _, err := f.db.ExecContext(ctx, `UPDATE canvas_ai_steps SET status='cancelled' WHERE project=$1 AND workspace_id=$2 AND run_id=$3`, f.project, f.workspace, run); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.db.ExecContext(ctx, `UPDATE canvas_ai_runs SET status='cancelled' WHERE project=$1 AND workspace_id=$2 AND id=$3`, f.project, f.workspace, run); err != nil {
+		t.Fatal(err)
+	}
+	if call(modelTestID(8601), 2, 409)["error"] != "migration_waiting_for_runs" {
+		t.Fatal("settling paid work changed the frozen rejection")
+	}
+	call(modelTestID(8602), 2, 200)
+	model := f.read(t)
+	if model.Versions[f.root] != 3 || len(model.Canvases) != 2 {
+		t.Fatal("explicit migration after execution settled lost its source version barrier")
+	}
+}

internal/platform/canvas_model_guard.go

@@ -0,0 +1,41 @@
+package platform
+
+import (
+	"net/http"
+	"strings"
+)
+
+// Old frozen receipts remain readable. Old whole-snapshot/ownership writers may
+// not edit a migrated tree, even when their old client has not seen the barrier.
+func (s *service) guardLegacyCanonicalRequest(w http.ResponseWriter, r *http.Request, project, account string) (bool, error) {
+	if r.PathValue("material") == "" {
+		return false, nil
+	}
+	path := r.URL.Path
+	legacy := strings.HasSuffix(path, "/canvas")
+	if r.Method != http.MethodGet {
+		for _, part := range []string{"/canvas/subgraphs", "/canvas/connections", "/canvas/transactions", "/canvas/operations"} {
+			legacy = legacy || strings.Contains(path, part)
+		}
+	}
+	if !legacy {
+		return false, nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return false, err
+	}
+	defer tx.Rollback()
+	if _, _, err = lockMaterial(r.Context(), tx, project, r.PathValue("workspace"), r.PathValue("material"), account); err != nil {
+		return false, err
+	}
+	root, err := canonicalRoot(r.Context(), tx, project, r.PathValue("workspace"), r.PathValue("material"))
+	if err != nil {
+		return false, err
+	}
+	if root == "" {
+		return false, nil
+	}
+	reply(w, 409, response{"error": "canonical_write_required", "root_id": root, "model_path": "canvas/model"})
+	return true, nil
+}

internal/platform/canvas_model_http.go

@@ -0,0 +1,496 @@
+package platform
+
+import (
+	"context"
+	"crypto/rand"
+	"database/sql"
+	"encoding/hex"
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+const modelMigrateAction = "model.migrate.v1"
+const modelEditAction = "model.operations.v2"
+
+func newModelID() string {
+	var value [16]byte
+	if _, err := rand.Read(value[:]); err != nil {
+		return ""
+	}
+	value[6], value[8] = value[6]&0x0f|0x40, value[8]&0x3f|0x80
+	text := hex.EncodeToString(value[:])
+	return text[:8] + "-" + text[8:12] + "-" + text[12:16] + "-" + text[16:20] + "-" + text[20:]
+}
+func legacyModelRoot(r *http.Request, tx *sql.Tx, project, workspace, board string) (string, error) {
+	seen := map[string]bool{}
+	for len(seen) <= 8 {
+		if seen[board] {
+			return "", errCanvasModel
+		}
+		seen[board] = true
+		relation, err := readSubgraphRelation(r, tx, project, workspace, board)
+		if err == sql.ErrNoRows {
+			return board, nil
+		}
+		if err != nil {
+			return "", err
+		}
+		if relation.Archived {
+			return "", sql.ErrNoRows
+		}
+		board = relation.Parent
+	}
+	return "", errCanvasModel
+}
+func collectLegacyModel(r *http.Request, tx *sql.Tx, project, workspace, root string) (map[string]canvasSnapshot, []subgraphRelation, error) {
+	rows, err := tx.QueryContext(r.Context(), `WITH RECURSIVE tree(id,path) AS (SELECT $3::uuid,ARRAY[$3::uuid] UNION ALL SELECT s.child_board_id,t.path||s.child_board_id FROM tree t JOIN canvas_subgraphs s ON s.project=$1 AND s.workspace_id=$2 AND s.parent_board_id=t.id WHERE s.archived_at IS NULL AND NOT s.child_board_id=ANY(t.path) AND cardinality(t.path)<=8) SELECT m.id::text,m.canvas_version,COALESCE(m.canvas_document,'{"schema_version":2,"nodes":[],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}'::jsonb) FROM tree t JOIN materials m ON m.project=$1 AND m.workspace_id=$2 AND m.id=t.id WHERE m.kind='board' ORDER BY m.id LIMIT 257`, project, workspace, root)
+	if err != nil {
+		return nil, nil, err
+	}
+	snapshots := map[string]canvasSnapshot{}
+	for rows.Next() {
+		var snapshot canvasSnapshot
+		if err = rows.Scan(&snapshot.BoardID, &snapshot.Version, &snapshot.Document); err != nil {
+			rows.Close()
+			return nil, nil, err
+		}
+		snapshots[snapshot.BoardID] = snapshot
+	}
+	err = rows.Err()
+	rows.Close()
+	if err != nil {
+		return nil, nil, err
+	}
+	if len(snapshots) == 0 || len(snapshots) > 256 {
+		return nil, nil, errGraphCapacity
+	}
+	rows, err = tx.QueryContext(r.Context(), `SELECT parent_board_id::text,frame_id,child_board_id::text FROM canvas_subgraphs WHERE project=$1 AND workspace_id=$2 AND archived_at IS NULL ORDER BY child_board_id`, project, workspace)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer rows.Close()
+	relations := []subgraphRelation{}
+	for rows.Next() {
+		var relation subgraphRelation
+		if err = rows.Scan(&relation.Parent, &relation.Frame, &relation.Child); err != nil {
+			return nil, nil, err
+		}
+		if _, exists := snapshots[relation.Parent]; exists {
+			relations = append(relations, relation)
+		}
+	}
+	return snapshots, relations, rows.Err()
+}
+func modelRequestRetry(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, workspace, account, root, action, key, hash string) (bool, error) {
+	var previousRoot, previousAction, previousHash string
+	var status int
+	var body json.RawMessage
+	err := tx.QueryRowContext(r.Context(), `SELECT root_id::text,action,payload_hash,response_status,response_body FROM canvas_model_requests WHERE project=$1 AND workspace_id=$2 AND account_id=$3 AND request_id=$4`, project, workspace, account, key).Scan(&previousRoot, &previousAction, &previousHash, &status, &body)
+	if err == sql.ErrNoRows {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	if previousRoot != root || previousAction != action || previousHash != hash {
+		reject(w, 409, "idempotency_conflict")
+		return true, nil
+	}
+	reply(w, status, body)
+	return true, nil
+}
+func commitModelReceipt(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, workspace, account, root, action, key, hash string, status int, body response) error {
+	body["request_id"], body["protocol_version"] = key, canvasModelProtocol
+	raw, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_model_requests(project,workspace_id,account_id,request_id,root_id,action,protocol_version,payload_hash,response_status,response_body) VALUES($1,$2,$3,$4,$5,$6,$7,$8,$9,$10)`, project, workspace, account, key, root, action, canvasModelProtocol, hash, status, raw)
+	if err != nil {
+		return err
+	}
+	if err = tx.Commit(); err != nil {
+		return err
+	}
+	reply(w, status, body)
+	return nil
+}
+func decodeModelRequest(w http.ResponseWriter, r *http.Request, input any) bool {
+	decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, canvasLimit))
+	decoder.DisallowUnknownFields()
+	if decoder.Decode(input) != nil || decoder.Decode(new(any)) != io.EOF {
+		reject(w, 400, "invalid_model_request")
+		return false
+	}
+	return true
+}
+
+func (s *service) getCanvasModel(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	kind, _, err := lockMaterial(r.Context(), tx, project, workspace, board, account)
+	if err != nil {
+		return err
+	}
+	if kind != "board" {
+		reject(w, 400, "invalid_material")
+		return nil
+	}
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, board)
+	if err != nil {
+		return err
+	}
+	if root == "" {
+		root, err = legacyModelRoot(r, tx, project, workspace, board)
+		if err != nil {
+			return err
+		}
+		snapshots, _, err := collectLegacyModel(r, tx, project, workspace, root)
+		if err != nil {
+			return err
+		}
+		versions := map[string]int64{}
+		for id, snapshot := range snapshots {
+			versions[id] = snapshot.Version
+		}
+		reply(w, 409, response{"error": "canonical_migration_required", "root_id": root, "source_versions": versions, "document_format_version": canvasModelFormat})
+		return nil
+	}
+	model, err := loadCanvasModel(r.Context(), tx, project, workspace, root)
+	if err != nil {
+		return err
+	}
+	if err = tx.Rollback(); err != nil {
+		return err
+	}
+	if r.Header.Get("Accept") == modelStreamType {
+		writeCanvasModelStream(r.Context(), w, model)
+		return nil
+	}
+	w.Header().Add("Vary", "Accept")
+	reply(w, 200, response{"model": model.view(nil)})
+	return nil
+}
+
+func (s *service) migrateCanonicalCanvas(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodPost {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	var input struct {
+		ProtocolVersion int              `json:"protocol_version"`
+		RequestID       string           `json:"request_id"`
+		Expected        map[string]int64 `json:"expected_versions"`
+	}
+	if !decodeModelRequest(w, r, &input) {
+		return nil
+	}
+	key := canvasIdempotencyKey(r)
+	if input.ProtocolVersion != canvasModelProtocol || !uuidSlugPattern.MatchString(key) || input.RequestID != key || len(input.Expected) == 0 || len(input.Expected) > 256 {
+		reject(w, 400, "invalid_model_migration")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	kind, role, err := lockMaterial(r.Context(), tx, project, workspace, board, account)
+	if err != nil {
+		return err
+	}
+	if kind != "board" {
+		reject(w, 400, "invalid_material")
+		return nil
+	}
+	if role == "viewer" {
+		reject(w, 403, "forbidden")
+		return nil
+	}
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, board)
+	if err != nil {
+		return err
+	}
+	already := root != ""
+	if !already {
+		root, err = legacyModelRoot(r, tx, project, workspace, board)
+		if err != nil {
+			return err
+		}
+	}
+	done, err := modelRequestRetry(w, r, tx, project, workspace, account, root, modelMigrateAction, key, payloadDigest(input))
+	if err != nil || done {
+		return err
+	}
+	rejectMigration := func(status int, code string) error {
+		return commitModelReceipt(w, r, tx, project, workspace, account, root, modelMigrateAction, key, payloadDigest(input), status, response{"status": "not-applied", "terminal": true, "error": code})
+	}
+	if already {
+		return rejectMigration(409, "canonical_migration_already_applied")
+	}
+	snapshots, relations, err := collectLegacyModel(r, tx, project, workspace, root)
+	if err != nil {
+		return err
+	}
+	if len(snapshots) != len(input.Expected) {
+		return rejectMigration(412, "migration_version_conflict")
+	}
+	for id, snapshot := range snapshots {
+		if input.Expected[id] != snapshot.Version {
+			return rejectMigration(412, "migration_version_conflict")
+		}
+	}
+	// Active or outcome-unknown paid work must settle before the identity barrier.
+	for id := range snapshots {
+		var busy bool
+		if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_ai_steps WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND status IN('queued','running'))`, project, workspace, id).Scan(&busy); err != nil {
+			return err
+		}
+		if busy {
+			return rejectMigration(409, "migration_waiting_for_runs")
+		}
+	}
+	migration, err := migrateCanvasModel(root, snapshots, relations, newModelID)
+	if err != nil {
+		return rejectMigration(422, "model_migration_failed")
+	}
+	versionsRaw, _ := json.Marshal(input.Expected)
+	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_model_projects(project,workspace_id,root_id,migration_id,source_versions) VALUES($1,$2,$3,$4,$5)`, project, workspace, root, key, versionsRaw)
+	if err != nil {
+		return err
+	}
+	before := emptyModel(root)
+	for id, snapshot := range snapshots {
+		before.Versions[id] = snapshot.Version
+	}
+	participants := map[string]bool{}
+	for id := range migration.Model.Canvases {
+		participants[id] = true
+	}
+	if err = s.saveCanvasModel(r, tx, project, workspace, account, before, migration.Model, participants); err != nil {
+		return err
+	}
+	for _, identity := range migration.Identities {
+		_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_model_identity_map(project,workspace_id,root_id,source_canvas_id,source_structure,source_element_id,element_id) VALUES($1,$2,$3,$4,$5,$6,$7)`, project, workspace, root, identity.SourceCanvasID, identity.Structure, identity.SourceID, identity.ElementID)
+		if err != nil {
+			return err
+		}
+	}
+	return commitModelReceipt(w, r, tx, project, workspace, account, root, modelMigrateAction, key, payloadDigest(input), 200, response{"status": "applied", "model": migration.Model.view(nil), "identity_map": migration.Identities, "source_versions": input.Expected})
+}
+
+func (s *service) submitCanvasModelOperations(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodPost {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	var input modelBatch
+	if !decodeModelRequest(w, r, &input) {
+		return nil
+	}
+	key := canvasIdempotencyKey(r)
+	if input.ProtocolVersion != canvasModelProtocol || !uuidSlugPattern.MatchString(key) || input.RequestID != key || len(input.Expected) == 0 || len(input.Expected) > 256 || len(input.Operations) == 0 || len(input.Operations) > 2500 {
+		reject(w, 400, "invalid_model_request")
+		return nil
+	}
+	for id, version := range input.Expected {
+		if !uuidSlugPattern.MatchString(id) || version < 0 || version > 9007199254740990 {
+			reject(w, 400, "invalid_model_version")
+			return nil
+		}
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	kind, role, err := lockMaterial(r.Context(), tx, project, workspace, board, account)
+	if err != nil {
+		return err
+	}
+	if kind != "board" {
+		reject(w, 400, "invalid_material")
+		return nil
+	}
+	if role == "viewer" {
+		reject(w, 403, "forbidden")
+		return nil
+	}
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, board)
+	if err != nil {
+		return err
+	}
+	if root == "" {
+		reject(w, 409, "canonical_migration_required")
+		return nil
+	}
+	done, err := modelRequestRetry(w, r, tx, project, workspace, account, root, modelEditAction, key, payloadDigest(input))
+	if err != nil || done {
+		return err
+	}
+	rejectBatch := func(status int, code string) error {
+		return commitModelReceipt(w, r, tx, project, workspace, account, root, modelEditAction, key, payloadDigest(input), status, response{"status": "not-applied", "terminal": true, "error": code})
+	}
+	before, err := loadCanvasModel(r.Context(), tx, project, workspace, root)
+	if err != nil {
+		return err
+	}
+	for id, expected := range input.Expected {
+		if before.Versions[id] != expected {
+			return rejectBatch(412, "version_conflict")
+		}
+	}
+	for _, operation := range input.Operations {
+		if !uuidSlugPattern.MatchString(operation.ID) {
+			return rejectBatch(400, "invalid_model_operation")
+		}
+		var used bool
+		if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_model_operations WHERE project=$1 AND workspace_id=$2 AND operation_id=$3)`, project, workspace, operation.ID).Scan(&used); err != nil {
+			return err
+		}
+		if used {
+			return rejectBatch(409, "operation_already_applied")
+		}
+	}
+	after, touched, err := applyModelOperations(before, input.Operations)
+	if err != nil {
+		code := "invalid_model_operation"
+		if err == errModelConflict {
+			code = "canvas_model_field_conflict"
+		}
+		return rejectBatch(409, code)
+	}
+	for id := range touched {
+		if _, exists := input.Expected[id]; !exists {
+			return rejectBatch(428, "version_required")
+		}
+	}
+	for id := range input.Expected {
+		if _, existed := before.Versions[id]; !existed {
+			if _, created := after.Canvases[id]; !created {
+				return rejectBatch(409, "invalid_model_participant")
+			}
+			var exists bool
+			if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM materials WHERE project=$1 AND workspace_id=$2 AND id=$3)`, project, workspace, id).Scan(&exists); err != nil {
+				return err
+			}
+			if exists {
+				return rejectBatch(409, "canvas_identity_conflict")
+			}
+		}
+		if !touched[id] {
+			touched[id] = true
+			after.Versions[id] = before.Versions[id] + 1
+		}
+	}
+	for id, element := range after.Elements {
+		if before.Elements[id] == nil {
+			var foreign bool
+			if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_model_elements WHERE project=$1 AND element_id=$2 AND (workspace_id<>$3 OR root_id<>$4))`, project, id, workspace, root).Scan(&foreign); err != nil {
+				return err
+			}
+			if foreign {
+				return rejectBatch(409, "element_identity_conflict")
+			}
+		}
+		if element["structure"] == "node" {
+			data := element["data"].(map[string]any)
+			if asset := modelString(data["assetId"]); asset != "" {
+				prior := before.Elements[id]
+				if prior == nil || !modelEqual(prior["data"].(map[string]any)["assetId"], data["assetId"]) {
+					readable, e := assetReadable(r, tx, project, workspace, asset, account)
+					if e != nil {
+						return e
+					}
+					if !readable {
+						return rejectBatch(400, "invalid_asset_reference")
+					}
+				}
+			}
+		}
+	}
+	for id := range after.DeadRecords {
+		if before.Elements[id] != nil || before.Tombstones[id] > 0 {
+			continue
+		}
+		var foreign bool
+		if err = tx.QueryRowContext(r.Context(), `SELECT EXISTS(SELECT 1 FROM canvas_model_elements WHERE project=$1 AND element_id=$2 AND (workspace_id<>$3 OR root_id<>$4))`, project, id, workspace, root).Scan(&foreign); err != nil {
+			return err
+		}
+		if foreign {
+			return rejectBatch(409, "element_identity_conflict")
+		}
+	}
+	if err = s.saveCanvasModel(r, tx, project, workspace, account, before, after, touched); err != nil {
+		return err
+	}
+	ids := []string{}
+	for _, operation := range input.Operations {
+		ids = append(ids, operation.ID)
+		_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_model_operations(project,workspace_id,operation_id,request_id,account_id) VALUES($1,$2,$3,$4,$5)`, project, workspace, operation.ID, key, account)
+		if err != nil {
+			return err
+		}
+	}
+	return commitModelReceipt(w, r, tx, project, workspace, account, root, modelEditAction, key, payloadDigest(input), 200, response{"status": "applied", "operation_ids": ids, "model": after.view(input.Expected)})
+}
+func (s *service) getCanvasModelOperation(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	key := r.PathValue("request")
+	if !uuidSlugPattern.MatchString(key) {
+		reject(w, 400, "invalid_request_id")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	if _, _, err = lockMaterial(r.Context(), tx, project, workspace, board, account); err != nil {
+		return err
+	}
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, board)
+	if err != nil {
+		return err
+	}
+	if root == "" {
+		root, err = legacyModelRoot(r, tx, project, workspace, board)
+		if err != nil {
+			return err
+		}
+	}
+	var body json.RawMessage
+	err = tx.QueryRowContext(r.Context(), `SELECT response_body FROM canvas_model_requests WHERE project=$1 AND workspace_id=$2 AND account_id=$3 AND request_id=$4 AND root_id=$5`, project, workspace, account, key, root).Scan(&body)
+	if err == sql.ErrNoRows {
+		reply(w, 404, response{"status": "unknown", "error": "operation_receipt_unknown", "request_id": key})
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	if err = tx.Rollback(); err != nil {
+		return err
+	}
+	reply(w, 200, body)
+	return nil
+}
+
+func modelExists(ctx context.Context, tx *sql.Tx, project, workspace, board string) (bool, error) {
+	root, err := canonicalRoot(ctx, tx, project, workspace, board)
+	return root != "", err
+}

internal/platform/canvas_model_integration_test.go

@@ -0,0 +1,398 @@
+package platform
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+)
+
+func TestCanonicalModelMigrationAndIncrementalLifecycle(t *testing.T) {
+	dsn := os.Getenv("PLATFORM_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("requires an isolated integration database")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	ctx := context.Background()
+	var entropy [12]byte
+	_, _ = rand.Read(entropy[:])
+	project := "canonical-" + hex.EncodeToString(entropy[:])
+	defer func() {
+		for _, table := range []string{"canvas_model_operations", "canvas_model_identity_map", "canvas_model_requests", "canvas_model_projects", "canvas_asset_bindings", "canvas_subgraphs", "workspaces", "project_accounts"} {
+			_, _ = db.ExecContext(ctx, "DELETE FROM "+table+" WHERE project=$1", project)
+		}
+	}()
+	var account, workspace, root string
+	if err = db.QueryRowContext(ctx, `INSERT INTO project_accounts(project,id) VALUES($1,gen_random_uuid()) RETURNING id::text`, project).Scan(&account); err != nil {
+		t.Fatal(err)
+	}
+	var tokenBytes [32]byte
+	_, _ = rand.Read(tokenBytes[:])
+	token := base64.RawURLEncoding.EncodeToString(tokenBytes[:])
+	hash := sha256.Sum256([]byte(token))
+	if _, err = db.ExecContext(ctx, `INSERT INTO project_sessions(token_hash,project,account_id,expires_at) VALUES($1,$2,$3,now()+interval '1 hour')`, base64.RawURLEncoding.EncodeToString(hash[:]), project, account); err != nil {
+		t.Fatal(err)
+	}
+	if err = db.QueryRowContext(ctx, `INSERT INTO workspaces(project,name,owner_id) VALUES($1,'Canonical',$2) RETURNING id::text`, project, account).Scan(&workspace); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = db.ExecContext(ctx, `INSERT INTO workspace_members(project,workspace_id,account_id,role) VALUES($1,$2,$3,'admin')`, project, workspace, account); err != nil {
+		t.Fatal(err)
+	}
+	legacy := json.RawMessage(`{"schema_version":1,"nodes":[` + modelLegacyFrame + `,{"id":"a","type":"plainText","position":{"x":150,"y":260},"width":240,"height":72,"data":{"kind":"plain-text","title":"a","text":"preserved","frameId":"f"}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`)
+	if err = db.QueryRowContext(ctx, `INSERT INTO materials(project,workspace_id,kind,title,created_by,canvas_document) VALUES($1,$2,'board','Root',$3,$4) RETURNING id::text`, project, workspace, account, legacy).Scan(&root); err != nil {
+		t.Fatal(err)
+	}
+	mux := http.NewServeMux()
+	Register(mux, db, map[string]string{project: "https://app.example.com/auth/callback"}, "https://api.example.com", nil)
+	base := "/projects/" + project + "/workspaces/" + workspace + "/materials/" + root + "/canvas"
+	call := func(method, path string, input any, key string, status int) response {
+		t.Helper()
+		raw, _ := json.Marshal(input)
+		request := httptest.NewRequest(method, path, bytes.NewReader(raw))
+		request.Header.Set("Authorization", "Bearer "+token)
+		request.Header.Set("Accept", "application/vnd.foundry.canvas+json;version=2")
+		if key != "" {
+			request.Header.Set("Idempotency-Key", key)
+		}
+		writer := httptest.NewRecorder()
+		mux.ServeHTTP(writer, request)
+		if writer.Code != status {
+			t.Fatalf("%s %s got %d %s want %d", method, path, writer.Code, writer.Body.String(), status)
+		}
+		out := response{}
+		if writer.Body.Len() > 0 {
+			if err := json.Unmarshal(writer.Body.Bytes(), &out); err != nil {
+				t.Fatal(err)
+			}
+		}
+		return out
+	}
+	read := func() canvasModel {
+		t.Helper()
+		tx, err := db.BeginTx(ctx, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer tx.Rollback()
+		model, err := loadCanvasModel(ctx, tx, project, workspace, root)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return model
+	}
+	if call("GET", base+"/model", nil, "", 409)["error"] != "canonical_migration_required" {
+		t.Fatal("legacy read silently migrated")
+	}
+	var count int
+	if err = db.QueryRowContext(ctx, `SELECT count(*) FROM canvas_model_projects WHERE project=$1`, project).Scan(&count); err != nil || count != 0 {
+		t.Fatal("GET created a canonical project")
+	}
+	migrationKey := modelTestID(1000)
+	migrationInput := response{"protocol_version": 2, "request_id": migrationKey, "expected_versions": map[string]int64{root: 1}}
+	migration := call("POST", base+"/model/migrate", migrationInput, migrationKey, 200)
+	if migration["status"] != "applied" {
+		t.Fatal("migration missing applied receipt")
+	}
+	retry := call("POST", base+"/model/migrate", migrationInput, migrationKey, 200)
+	if !modelEqual(migration["identity_map"], retry["identity_map"]) {
+		t.Fatal("migration retry allocated a second identity map")
+	}
+	identities := migration["identity_map"].([]any)
+	nodeID, frameID := "", ""
+	for _, item := range identities {
+		mapping := item.(map[string]any)
+		switch mapping["sourceId"] {
+		case "a":
+			nodeID = mapping["elementId"].(string)
+		case "f":
+			frameID = mapping["elementId"].(string)
+		}
+	}
+	model := read()
+	if nodeID == "" || frameID == "" || len(model.Canvases) != 2 {
+		t.Fatal("migration lost identities or an implicit partition")
+	}
+	child := modelString(model.Elements[nodeID]["ownerCanvasId"])
+	if child == root || model.Canvases[child].Parent.EntryElementID != frameID || model.Versions[root] != 2 || model.Versions[child] != 1 {
+		t.Fatal("canonical owning tree or version barrier is incorrect")
+	}
+	if call("PATCH", base, response{"document": legacy}, "", 409)["error"] != "canonical_write_required" {
+		t.Fatal("old snapshot writer can overwrite canonical records")
+	}
+	call("GET", base, nil, "", 409)
+	if _, err = db.ExecContext(ctx, `UPDATE materials SET canvas_document=$4,canvas_version=canvas_version+1 WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, root, legacy); err == nil {
+		t.Fatal("database identity barrier allowed an old writer")
+	}
+	edit := func(n int, versions map[string]int64, changes ...modelChange) response {
+		t.Helper()
+		key := modelTestID(n)
+		input := modelBatch{ProtocolVersion: 2, RequestID: key, Expected: versions, Operations: []modelOperation{{ID: modelTestID(n + 10000), Changes: changes}}}
+		return call("POST", base+"/model/operations", input, key, 200)
+	}
+	titleChange := modelChange{Kind: "field", Target: modelTarget{ID: nodeID, Incarnation: 1}, Field: "data.title", Before: modelJSON("a"), After: modelJSON("renamed")}
+	first := edit(1001, map[string]int64{child: 1}, titleChange)
+	if first["model"].(map[string]any)["complete"] != false {
+		t.Fatal("operation receipt pretends to be a full project snapshot")
+	}
+	model = read()
+	if model.Versions[root] != 2 || model.Versions[child] != 2 || model.Elements[nodeID]["data"].(map[string]any)["text"] != "preserved" {
+		t.Fatal("child edit changed unrelated canvas/version/content")
+	}
+	requestKey := modelTestID(1001)
+	repeat := modelBatch{ProtocolVersion: 2, RequestID: requestKey, Expected: map[string]int64{child: 1}, Operations: []modelOperation{{ID: modelTestID(11001), Changes: []modelChange{titleChange}}}}
+	call("POST", base+"/model/operations", repeat, requestKey, 200)
+	if read().Versions[child] != 2 {
+		t.Fatal("exact retry executed twice")
+	}
+	if call("GET", base+"/model/operations/"+requestKey, nil, "", 200)["status"] != "applied" {
+		t.Fatal("lost ACK cannot be queried")
+	}
+	if call("GET", base+"/model/operations/"+modelTestID(9999), nil, "", 404)["status"] != "unknown" {
+		t.Fatal("missing receipt claimed zero writes")
+	}
+	// Move is a row owner update, retaining ElementId and incarnation.
+	geometry := model.Elements[nodeID]["geometry"]
+	edit(1002, map[string]int64{root: 2, child: 2}, modelChange{Kind: "field", Target: modelTarget{ID: nodeID, Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(child), After: modelJSON(root)}, modelChange{Kind: "field", Target: modelTarget{ID: nodeID, Incarnation: 1}, Field: "geometry", Before: modelJSON(geometry), After: modelJSON(map[string]any{"x": 150, "y": 260, "width": 240, "height": 72, "rotation": 0})})
+	model = read()
+	if model.Elements[nodeID]["ownerCanvasId"] != root || modelInt(model.Elements[nodeID]["incarnation"]) != 1 {
+		t.Fatal("move recreated the element")
+	}
+	// Future component/envelope bytes survive editing another object and legacy projections.
+	opaqueID := modelTestID(3000)
+	opaque := modelTestNode(opaqueID, root)
+	opaque["componentId"], opaque["dataVersion"], opaque["data"], opaque["futureEnvelope"] = "future.plugin", float64(9), map[string]any{"raw": []any{map[string]any{"keep": true}}}, map[string]any{"extension": "retained"}
+	edit(1003, map[string]int64{root: 3}, modelChange{Kind: "element", ID: opaqueID, Before: modelJSON(nil), After: modelJSON(opaque)})
+	model = read()
+	if !modelEqual(model.Elements[opaqueID], opaque) {
+		t.Fatal("future component data changed")
+	}
+	edit(1004, map[string]int64{root: 4}, modelChange{Kind: "element", ID: nodeID, Before: modelJSON(model.Elements[nodeID]), After: modelJSON(nil)})
+	model = read()
+	if model.Tombstones[nodeID] != 1 {
+		t.Fatal("delete did not persist its lifecycle tombstone")
+	}
+	restored := modelTestNode(nodeID, root)
+	restored["componentId"] = "plain-text"
+	restored["incarnation"] = float64(2)
+	restored["data"].(map[string]any)["title"] = "restored"
+	edit(1005, map[string]int64{root: 5}, modelChange{Kind: "element", ID: nodeID, Before: modelJSON(nil), After: modelJSON(restored)})
+	staleKey := modelTestID(1006)
+	stale := modelBatch{ProtocolVersion: 2, RequestID: staleKey, Expected: map[string]int64{root: 6}, Operations: []modelOperation{{ID: modelTestID(11006), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: nodeID, Incarnation: 1}, Field: "data.title", Before: modelJSON("restored"), After: modelJSON("stale callback")}}}}}
+	if call("POST", base+"/model/operations", stale, staleKey, 409)["status"] != "not-applied" {
+		t.Fatal("stale callback did not receive a zero-write receipt")
+	}
+	if call("GET", base+"/model/operations/"+staleKey, nil, "", 200)["terminal"] != true {
+		t.Fatal("terminal rejection was not queryable")
+	}
+	model = read()
+	if model.Versions[root] != 6 || !modelEqual(model.Elements[opaqueID], opaque) || modelInt(model.Elements[nodeID]["incarnation"]) != 2 {
+		t.Fatal("stale callback or unrelated update damaged state")
+	}
+	duplicateKey := modelTestID(1007)
+	duplicate := modelBatch{ProtocolVersion: 2, RequestID: duplicateKey, Expected: map[string]int64{root: 6}, Operations: []modelOperation{{ID: modelTestID(11002), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: nodeID, Incarnation: 2}, Field: "data.title", Before: modelJSON("restored"), After: modelJSON("duplicate effect")}}}}}
+	if call("POST", base+"/model/operations", duplicate, duplicateKey, 409)["error"] != "operation_already_applied" {
+		t.Fatal("logical operation was executed under a new request ID")
+	}
+	var owner string
+	var incarnation int64
+	if err = db.QueryRowContext(ctx, `SELECT owner_canvas_id::text,incarnation FROM canvas_model_elements WHERE project=$1 AND element_id=$2 AND NOT deleted`, project, nodeID).Scan(&owner, &incarnation); err != nil || owner != root || incarnation != 2 {
+		t.Fatal("canonical row authority disagrees with the API")
+	}
+	if call("GET", base+"/model", nil, "", 200)["model"].(map[string]any)["complete"] != true {
+		t.Fatal("initial read has no explicit coverage")
+	}
+	// Negotiate the same authenticated canonical read as a streamed transfer.
+	streamRequest := httptest.NewRequest("GET", base+"/model", nil)
+	streamRequest.Header.Set("Authorization", "Bearer "+token)
+	streamRequest.Header.Set("Accept", modelStreamType)
+	streamWriter := httptest.NewRecorder()
+	mux.ServeHTTP(streamWriter, streamRequest)
+	streamed := streamRecords(t, streamWriter)
+	if streamWriter.Code != 200 || streamWriter.Header().Get("Content-Type") != modelStreamType || len(streamed) < 2 || streamed[0]["projectId"] != root || streamed[len(streamed)-1]["kind"] != "complete" || !modelEqual(streamed[0]["versions"], read().Versions) {
+		t.Fatal("authenticated stream lost canonical snapshot coverage")
+	}
+	// An object created and removed inside one transaction still has a lifecycle fact.
+	ghostID := modelTestID(4000)
+	ghost := modelTestNode(ghostID, root)
+	edit(1008, map[string]int64{root: 6}, modelChange{Kind: "element", ID: ghostID, Before: modelJSON(nil), After: modelJSON(ghost)}, modelChange{Kind: "element", ID: ghostID, Before: modelJSON(ghost), After: modelJSON(nil)})
+	model = read()
+	if model.Tombstones[ghostID] != 1 || model.Elements[ghostID] != nil {
+		t.Fatal("in-batch create/delete lost its tombstone")
+	}
+	ghost["incarnation"] = float64(2)
+	edit(1009, map[string]int64{root: 7}, modelChange{Kind: "element", ID: ghostID, Before: modelJSON(nil), After: modelJSON(ghost)})
+	if modelInt(read().Elements[ghostID]["incarnation"]) != 2 {
+		t.Fatal("restore after an in-batch delete did not preserve identity")
+	}
+	// Session changes cannot send an old account's queued request as a new account.
+	request := httptest.NewRequest("GET", base+"/model", nil)
+	request.Header.Set("Authorization", "Bearer "+token)
+	request.Header.Set("X-Expected-Account", modelTestID(7777))
+	writer := httptest.NewRecorder()
+	mux.ServeHTTP(writer, request)
+	if writer.Code != 409 {
+		t.Fatal("expected-account barrier was ignored")
+	}
+	// A new partition's entry, owning canvas and versions publish atomically.
+	newCanvas, newFrame := modelTestID(5000), modelTestID(5001)
+	frame := modelTestNode(newFrame, root)
+	frame["componentId"] = "frame"
+	canvas := modelCanvas{ID: newCanvas, Parent: &modelParent{CanvasID: root, EntryElementID: newFrame}}
+	edit(1010, map[string]int64{root: 8, newCanvas: 0}, modelChange{Kind: "canvas", ID: newCanvas, Before: modelJSON(nil), After: modelJSON(canvas)}, modelChange{Kind: "element", ID: newFrame, Before: modelJSON(nil), After: modelJSON(frame)})
+	model = read()
+	if model.Versions[newCanvas] != 1 || model.Canvases[newCanvas].Parent.EntryElementID != newFrame {
+		t.Fatal("partition creation was not atomic")
+	}
+	edit(1011, map[string]int64{root: 9, newCanvas: 1}, modelChange{Kind: "canvas", ID: newCanvas, Before: modelJSON(canvas), After: modelJSON(nil)}, modelChange{Kind: "element", ID: newFrame, Before: modelJSON(frame), After: modelJSON(nil)})
+	model = read()
+	if _, exists := model.Canvases[newCanvas]; exists || model.Versions[newCanvas] != 2 {
+		t.Fatal("partition archive lost its version fence")
+	}
+	frame["incarnation"] = float64(2)
+	edit(1012, map[string]int64{root: 10, newCanvas: 2}, modelChange{Kind: "element", ID: newFrame, Before: modelJSON(nil), After: modelJSON(frame)}, modelChange{Kind: "canvas", ID: newCanvas, Before: modelJSON(nil), After: modelJSON(canvas)})
+	model = read()
+	if model.Versions[newCanvas] != 3 || modelInt(model.Elements[newFrame]["incarnation"]) != 2 {
+		t.Fatal("partition restore reused a stale lifecycle or version")
+	}
+
+	// A cross-scale entry move writes ownership, child binding and presentation units together.
+	innerCanvas, innerFrame, memberID := modelTestID(5100), modelTestID(5101), modelTestID(5102)
+	container := modelTestNode(innerFrame, root)
+	container["componentId"] = "frame"
+	originalPresentation := response{"contentScale": .75, "future": response{"keep": "metadata"}}
+	container["data"].(map[string]any)["presentation"] = originalPresentation
+	member := modelTestNode(memberID, innerCanvas)
+	member["data"].(map[string]any)["fontSize"] = float64(17)
+	inner := modelCanvas{ID: innerCanvas, Parent: &modelParent{CanvasID: root, EntryElementID: innerFrame}}
+	absent := false
+	edit(1013, map[string]int64{root: model.Versions[root], newCanvas: model.Versions[newCanvas], innerCanvas: 0},
+		modelChange{Kind: "field", Target: modelTarget{ID: newFrame, Incarnation: 2}, Field: "data.presentation", Before: modelJSON(nil), BeforePresent: &absent, After: modelJSON(response{"contentScale": 2})},
+		modelChange{Kind: "element", ID: innerFrame, Before: modelJSON(nil), After: modelJSON(container)},
+		modelChange{Kind: "canvas", ID: innerCanvas, Before: modelJSON(nil), After: modelJSON(inner)},
+		modelChange{Kind: "element", ID: memberID, Before: modelJSON(nil), After: modelJSON(member)})
+	model = read()
+	oldGeometry := model.Elements[innerFrame]["geometry"]
+	containerGeometry := oldGeometry.(map[string]any)
+	normalizedGeometry := response{"x": (containerGeometry["x"].(float64) - 24) / 2, "y": (containerGeometry["y"].(float64) - 36) / 2, "width": containerGeometry["width"].(float64) / 2, "height": containerGeometry["height"].(float64) / 2, "rotation": containerGeometry["rotation"]}
+	normalizedPresentation := response{"contentScale": .75, "unitScale": .5, "future": response{"keep": "metadata"}}
+	movedInner := inner
+	movedInner.Parent = &modelParent{CanvasID: newCanvas, EntryElementID: innerFrame}
+	edit(1014, map[string]int64{root: model.Versions[root], newCanvas: model.Versions[newCanvas], innerCanvas: model.Versions[innerCanvas]},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(root), After: modelJSON(newCanvas)},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "geometry", Before: modelJSON(oldGeometry), After: modelJSON(normalizedGeometry)},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "data.presentation", Before: modelJSON(originalPresentation), After: modelJSON(normalizedPresentation)},
+		modelChange{Kind: "canvas", ID: innerCanvas, Before: modelJSON(inner), After: modelJSON(movedInner)})
+	model = read()
+	if modelString(model.Elements[innerFrame]["ownerCanvasId"]) != newCanvas || model.Canvases[innerCanvas].Parent.CanvasID != newCanvas || !modelEqual(model.Elements[innerFrame]["data"].(map[string]any)["presentation"], normalizedPresentation) || !modelEqual(model.Elements[memberID], member) {
+		t.Fatal("scaled container move changed its member or lost the atomic unit/ownership boundary")
+	}
+	if call("GET", base+"/model/operations/"+modelTestID(1014), nil, "", 200)["status"] != "applied" {
+		t.Fatal("scaled move receipt was not queryable by its original identity")
+	}
+	edit(1015, map[string]int64{root: model.Versions[root], newCanvas: model.Versions[newCanvas], innerCanvas: model.Versions[innerCanvas]},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(newCanvas), After: modelJSON(root)},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "geometry", Before: modelJSON(normalizedGeometry), After: modelJSON(oldGeometry)},
+		modelChange{Kind: "field", Target: modelTarget{ID: innerFrame, Incarnation: 1}, Field: "data.presentation", Before: modelJSON(normalizedPresentation), After: modelJSON(originalPresentation)},
+		modelChange{Kind: "canvas", ID: innerCanvas, Before: modelJSON(movedInner), After: modelJSON(inner)})
+	model = read()
+	if _, exists := model.Elements[innerFrame]["data"].(map[string]any)["presentation"].(map[string]any)["unitScale"]; exists || !modelEqual(model.Elements[memberID], member) || model.Canvases[innerCanvas].Parent.CanvasID != root {
+		t.Fatal("scaled move inverse did not restore absent unit metadata and the original child binding")
+	}
+	// Several logical edits share one atomic request while retaining every deduplication identity.
+	batchKey, firstLogical, secondLogical := modelTestID(1016), modelTestID(22001), modelTestID(22002)
+	batchVersion := model.Versions[innerCanvas]
+	batch := modelBatch{ProtocolVersion: 2, RequestID: batchKey, Expected: map[string]int64{innerCanvas: batchVersion}, Operations: []modelOperation{
+		{ID: firstLogical, Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON(memberID), After: modelJSON("intermediate")}}},
+		{ID: secondLogical, Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON("intermediate"), After: modelJSON("batched")}}},
+	}}
+	batched := call("POST", base+"/model/operations", batch, batchKey, 200)
+	if !modelEqual(batched["operation_ids"], []string{firstLogical, secondLogical}) {
+		t.Fatal("batch receipt did not cover every original logical ID")
+	}
+	model = read()
+	if model.Versions[innerCanvas] != batchVersion+1 || modelString(model.Elements[memberID]["data"].(map[string]any)["title"]) != "batched" {
+		t.Fatal("batch lost ordered conditions or advanced the canvas version more than once")
+	}
+	if !modelEqual(call("GET", base+"/model/operations/"+batchKey, nil, "", 200), batched) || !modelEqual(call("POST", base+"/model/operations", batch, batchKey, 200), batched) {
+		t.Fatal("batch query/retry did not return its original receipt")
+	}
+	batch.RequestID = modelTestID(1017)
+	batch.Expected[innerCanvas] = model.Versions[innerCanvas]
+	batch.Operations = batch.Operations[:1]
+	if call("POST", base+"/model/operations", batch, batch.RequestID, 409)["error"] != "operation_already_applied" {
+		t.Fatal("a covered logical ID was executable under a new request key")
+	}
+	// A later failed condition cannot publish the earlier edit or consume its logical identity.
+	failedKey := modelTestID(1018)
+	batch.RequestID = failedKey
+	batch.Operations = []modelOperation{
+		{ID: modelTestID(22003), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON("batched"), After: modelJSON("must roll back")}}},
+		{ID: modelTestID(22004), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON("wrong before"), After: modelJSON("invalid")}}},
+	}
+	if call("POST", base+"/model/operations", batch, failedKey, 409)["status"] != "not-applied" {
+		t.Fatal("failed batch did not produce a zero-write terminal receipt")
+	}
+	model = read()
+	if model.Versions[innerCanvas] != batchVersion+1 || modelString(model.Elements[memberID]["data"].(map[string]any)["title"]) != "batched" {
+		t.Fatal("a failed batch leaked its successful prefix")
+	}
+	var consumed int
+	if err = db.QueryRowContext(ctx, `SELECT count(*) FROM canvas_model_operations WHERE project=$1 AND operation_id=$2`, project, modelTestID(22003)).Scan(&consumed); err != nil || consumed != 0 {
+		t.Fatal("a rejected atomic prefix consumed a logical operation ID")
+	}
+
+	// A compacted wire projection retains prefix IDs with conditional no-ops, including in a child scope.
+	projectedKey, guardLogical, effectLogical := modelTestID(1019), modelTestID(22005), modelTestID(22006)
+	projectedGhost := modelTestID(5200)
+	finalGhost := modelTestNode(projectedGhost, innerCanvas)
+	finalGhost["data"].(map[string]any)["text"] = "composed final value"
+	parentVersion := model.Versions[root]
+	projection := modelBatch{ProtocolVersion: 2, RequestID: projectedKey, Expected: map[string]int64{innerCanvas: model.Versions[innerCanvas]}, Operations: []modelOperation{
+		{ID: guardLogical, Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON("batched"), After: modelJSON("batched")}}},
+		{ID: effectLogical, Changes: []modelChange{
+			{Kind: "field", Target: modelTarget{ID: memberID, Incarnation: 1}, Field: "data.title", Before: modelJSON("batched"), After: modelJSON("projected final")},
+			{Kind: "element", ID: projectedGhost, Before: modelJSON(nil), After: modelJSON(finalGhost)},
+			{Kind: "element", ID: projectedGhost, Before: modelJSON(finalGhost), After: modelJSON(nil)},
+		}},
+	}}
+	projectedReceipt := call("POST", base+"/model/operations", projection, projectedKey, 200)
+	model = read()
+	if !modelEqual(projectedReceipt["operation_ids"], []string{guardLogical, effectLogical}) || model.Versions[innerCanvas] != batchVersion+2 || model.Versions[root] != parentVersion {
+		t.Fatal("projected prefix lost its logical coverage or widened the child writer scope")
+	}
+	if modelString(model.Elements[memberID]["data"].(map[string]any)["title"]) != "projected final" || model.Tombstones[projectedGhost] != 1 || !modelEqual(model.DeadRecords[projectedGhost], finalGhost) {
+		t.Fatal("projected effect lost final data, tombstone or archived lifecycle record")
+	}
+	if !modelEqual(call("GET", base+"/model/operations/"+projectedKey, nil, "", 200), projectedReceipt) {
+		t.Fatal("compacted projection receipt was not recoverable by its original key")
+	}
+
+	// A locally canceled incarnation was never sent; undo may first publish incarnation 2.
+	locallyElidedID := modelTestID(5201)
+	locallyRestored := modelTestNode(locallyElidedID, innerCanvas)
+	locallyRestored["incarnation"] = float64(2)
+	edit(1020, map[string]int64{innerCanvas: model.Versions[innerCanvas]}, modelChange{Kind: "element", ID: locallyElidedID, Before: modelJSON(nil), After: modelJSON(locallyRestored)})
+	model = read()
+	if modelInt(model.Elements[locallyElidedID]["incarnation"]) != 2 || model.Tombstones[locallyElidedID] != 0 {
+		t.Fatal("local elision undo reused a canceled life or invented an ACK tombstone")
+	}
+	staleElisionKey := modelTestID(1021)
+	staleElision := modelBatch{ProtocolVersion: 2, RequestID: staleElisionKey, Expected: map[string]int64{innerCanvas: model.Versions[innerCanvas]}, Operations: []modelOperation{{ID: modelTestID(22007), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: locallyElidedID, Incarnation: 1}, Field: "data.title", Before: modelJSON(locallyElidedID), After: modelJSON("stale local callback")}}}}}
+	if call("POST", base+"/model/operations", staleElision, staleElisionKey, 409)["status"] != "not-applied" || !modelEqual(read().Elements[locallyElidedID], locallyRestored) {
+		t.Fatal("a callback from the locally canceled incarnation changed its restored successor")
+	}
+
+}

internal/platform/canvas_model_migration.go

@@ -0,0 +1,282 @@
+package platform
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+type modelIdentity struct {
+	SourceCanvasID string `json:"sourceCanvasId"`
+	Structure      string `json:"structure"`
+	SourceID       string `json:"sourceId"`
+	ElementID      string `json:"elementId"`
+}
+type modelMigration struct {
+	Model       canvasModel
+	Identities  []modelIdentity
+	NewCanvases []string
+}
+type modelSpace struct{ X, Y, Scale float64 }
+
+// No source document is changed. IDs are allocated once inside the eventual
+// migration transaction and the complete mapping is stored with its receipt.
+func migrateCanvasModel(root string, snapshots map[string]canvasSnapshot, relations []subgraphRelation, allocate func() string) (modelMigration, error) {
+	result := modelMigration{Model: emptyModel(root), Identities: []modelIdentity{}, NewCanvases: []string{}}
+	documents, nodes := map[string]map[string]any{}, map[string]map[string]any{}
+	identities, children, synthetic := map[string]string{}, map[string]string{}, map[string]bool{}
+	used := map[string]bool{}
+	for board := range snapshots {
+		used[board] = true
+	}
+	nextID := func() (string, error) {
+		id := allocate()
+		if !uuidSlugPattern.MatchString(id) || used[id] {
+			return "", errCanvasModel
+		}
+		used[id] = true
+		return id, nil
+	}
+	identityKey := func(board, structure, id string) string { return board + "/" + structure + "/" + id }
+	for _, board := range sortedKeys(snapshots) {
+		if !uuidSlugPattern.MatchString(board) || snapshots[board].Version < 1 {
+			return result, errCanvasModel
+		}
+		normalized, valid := normalizeCanvas(snapshots[board].Document)
+		if !valid {
+			return result, errCanvasModel
+		}
+		var document map[string]any
+		if json.Unmarshal(normalized, &document) != nil {
+			return result, errCanvasModel
+		}
+		documents[board] = document
+		result.Model.Canvases[board] = modelCanvas{ID: board}
+		result.Model.Versions[board] = snapshots[board].Version + 1
+		for _, collection := range []string{"nodes", "edges"} {
+			structure := "node"
+			if collection == "edges" {
+				structure = "connection"
+			}
+			for _, value := range document[collection].([]any) {
+				record := value.(map[string]any)
+				old := record["id"].(string)
+				id, err := nextID()
+				if err != nil {
+					return result, err
+				}
+				identities[identityKey(board, structure, old)] = id
+				result.Identities = append(result.Identities, modelIdentity{SourceCanvasID: board, Structure: structure, SourceID: old, ElementID: id})
+				if structure == "node" {
+					nodes[canvasNodeKey(board, old)] = record
+				}
+			}
+		}
+	}
+	for _, relation := range relations {
+		if relation.Archived {
+			continue
+		}
+		key := canvasNodeKey(relation.Parent, relation.Frame)
+		frame := nodes[key]
+		if frame == nil || documents[relation.Child] == nil || children[key] != "" || relation.Child == root {
+			return result, errCanvasModel
+		}
+		data := frame["data"].(map[string]any)
+		sub, _ := data["subgraph"].(map[string]any)
+		if data["kind"] != "frame" || sub["boardId"] != relation.Child || result.Model.Canvases[relation.Child].Parent != nil {
+			return result, errCanvasModel
+		}
+		children[key] = relation.Child
+		result.Model.Canvases[relation.Child] = modelCanvas{ID: relation.Child, Parent: &modelParent{CanvasID: relation.Parent, EntryElementID: identities[identityKey(relation.Parent, "node", relation.Frame)]}}
+	}
+	// Ordinary legacy frameId groups also become actual canvases, even if empty.
+	for _, key := range sortedKeys(nodes) {
+		node := nodes[key]
+		data := node["data"].(map[string]any)
+		if data["kind"] != "frame" {
+			continue
+		}
+		if _, linked := data["subgraph"]; linked && children[key] == "" {
+			return result, errCanvasModel
+		}
+		if children[key] != "" {
+			continue
+		}
+		id, err := nextID()
+		if err != nil {
+			return result, err
+		}
+		board := strings.SplitN(key, "/", 2)[0]
+		children[key], synthetic[key] = id, true
+		result.Model.Canvases[id] = modelCanvas{ID: id, Parent: &modelParent{CanvasID: board, EntryElementID: identities[identityKey(board, "node", node["id"].(string))]}}
+		result.Model.Versions[id] = 1
+		result.NewCanvases = append(result.NewCanvases, id)
+	}
+	for _, board := range sortedKeys(documents) {
+		for index, value := range documents[board]["nodes"].([]any) {
+			node := value.(map[string]any)
+			original := node["data"].(map[string]any)
+			data := map[string]any{}
+			for key, value := range original {
+				data[key] = value
+			}
+			kind := data["kind"].(string)
+			owner := board
+			geometry := legacyModelGeometry(node, kind)
+			if frameID, exists := data["frameId"].(string); exists {
+				frame := nodes[canvasNodeKey(board, frameID)]
+				child := children[canvasNodeKey(board, frameID)]
+				if frame == nil || child == "" {
+					return result, errCanvasModel
+				}
+				position := frame["position"].(map[string]any)
+				frameData := frame["data"].(map[string]any)
+				scale := modelContentScale(frameData)
+				geometry["x"] = (geometry["x"].(float64) - position["x"].(float64) - 24) / scale
+				geometry["y"] = (geometry["y"].(float64) - position["y"].(float64) - 36) / scale
+				geometry["width"], geometry["height"] = geometry["width"].(float64)/scale, geometry["height"].(float64)/scale
+				owner = child
+			}
+			for _, key := range []string{"kind", "rotation", "frameId", "subgraph", "ports"} {
+				delete(data, key)
+			}
+			id := identities[identityKey(board, "node", node["id"].(string))]
+			result.Model.Elements[id] = map[string]any{"id": id, "incarnation": float64(1), "ownerCanvasId": owner, "componentId": kind, "dataVersion": float64(1), "structure": "node", "geometry": geometry, "data": data, "orderKey": fmt.Sprintf("%s/%012d", board, index)}
+		}
+	}
+	spaces, err := modelSpaces(result.Model)
+	if err != nil {
+		return result, err
+	}
+	resolve := func(board, node, handle, direction string) (map[string]any, error) {
+		seen := map[string]bool{}
+		for depth := 0; depth <= 8; depth++ {
+			key := canvasNodeKey(board, node)
+			legacy := nodes[key]
+			if legacy == nil || seen[key+"/"+handle] {
+				return nil, errCanvasModel
+			}
+			seen[key+"/"+handle] = true
+			data := legacy["data"].(map[string]any)
+			if data["kind"] != "frame" || !strings.HasPrefix(handle, "port:") {
+				endpoint := map[string]any{"elementId": identities[identityKey(board, "node", node)]}
+				if handle != "" {
+					endpoint["portId"] = handle
+				}
+				return endpoint, nil
+			}
+			ports, _ := data["ports"].([]any)
+			found := false
+			for _, value := range ports {
+				port := value.(map[string]any)
+				if port["id"] == strings.TrimPrefix(handle, "port:") && port["direction"] == direction {
+					node, handle = modelString(port["nodeId"]), modelString(port["handle"])
+					if !synthetic[key] {
+						board = children[key]
+					}
+					found = true
+					break
+				}
+			}
+			if !found {
+				return nil, errCanvasModel
+			}
+		}
+		return nil, errCanvasModel
+	}
+	for _, board := range sortedKeys(documents) {
+		for index, value := range documents[board]["edges"].([]any) {
+			edge := value.(map[string]any)
+			source, err := resolve(board, modelString(edge["source"]), modelString(edge["sourceHandle"]), "output")
+			if err != nil {
+				return result, err
+			}
+			target, err := resolve(board, modelString(edge["target"]), modelString(edge["targetHandle"]), "input")
+			if err != nil {
+				return result, err
+			}
+			owner, err := modelCommonCanvas(result.Model, modelString(result.Model.Elements[source["elementId"].(string)]["ownerCanvasId"]), modelString(result.Model.Elements[target["elementId"].(string)]["ownerCanvasId"]))
+			if err != nil {
+				return result, err
+			}
+			from, to := spaces[board], spaces[owner]
+			projectEdgePath(edge, from.Scale/to.Scale, (from.X-to.X)/to.Scale, (from.Y-to.Y)/to.Scale)
+			data, _ := edge["data"].(map[string]any)
+			if data == nil {
+				data = map[string]any{}
+			}
+			path := data["path"]
+			delete(data, "path")
+			id := identities[identityKey(board, "connection", edge["id"].(string))]
+			result.Model.Elements[id] = map[string]any{"id": id, "incarnation": float64(1), "ownerCanvasId": owner, "componentId": "connection", "dataVersion": float64(1), "structure": "connection", "source": source, "target": target, "path": path, "data": data, "orderKey": fmt.Sprintf("%s/%012d", board, index)}
+		}
+	}
+	if err := validateCanvasModel(result.Model); err != nil {
+		return result, err
+	}
+	return result, nil
+}
+func modelContentScale(data map[string]any) float64 {
+	presentation, _ := data["presentation"].(map[string]any)
+	if scale, ok := presentation["contentScale"].(float64); ok && scale > 0 {
+		return scale
+	}
+	return 1
+}
+func legacyModelGeometry(node map[string]any, kind string) map[string]any {
+	width, height := float64(260), float64(200)
+	switch kind {
+	case "plain-text":
+		width, height = 240, 72
+	case "plain-image":
+		width, height = 320, 240
+	case "icon":
+		width, height = 80, 80
+	case "frame":
+		width, height = 640, 400
+	}
+	if value, exists := node["width"].(float64); exists {
+		width = value
+	}
+	if value, exists := node["height"].(float64); exists {
+		height = value
+	}
+	position := node["position"].(map[string]any)
+	data := node["data"].(map[string]any)
+	rotation, _ := data["rotation"].(float64)
+	return map[string]any{"x": position["x"], "y": position["y"], "width": width, "height": height, "rotation": rotation}
+}
+func modelSpaces(model canvasModel) (map[string]modelSpace, error) {
+	result := map[string]modelSpace{model.Root: {Scale: 1}}
+	remaining := len(model.Canvases) - 1
+	for depth := 0; remaining > 0 && depth < 9; depth++ {
+		progress := false
+		for _, id := range sortedKeys(model.Canvases) {
+			canvas := model.Canvases[id]
+			if _, exists := result[id]; exists || canvas.Parent == nil {
+				continue
+			}
+			parent, exists := result[canvas.Parent.CanvasID]
+			if !exists {
+				continue
+			}
+			entry := model.Elements[canvas.Parent.EntryElementID]
+			if entry == nil {
+				return nil, errCanvasModel
+			}
+			geometry := entry["geometry"].(map[string]any)
+			data := entry["data"].(map[string]any)
+			result[id] = modelSpace{X: parent.X + (geometry["x"].(float64)+24)*parent.Scale, Y: parent.Y + (geometry["y"].(float64)+36)*parent.Scale, Scale: parent.Scale * modelContentScale(data)}
+			remaining--
+			progress = true
+		}
+		if !progress {
+			return nil, errCanvasModel
+		}
+	}
+	if remaining != 0 {
+		return nil, errCanvasModel
+	}
+	return result, nil
+}

internal/platform/canvas_model_store.go

@@ -0,0 +1,320 @@
+package platform
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"net/http"
+	"sort"
+)
+
+func canonicalRoot(ctx context.Context, tx *sql.Tx, project, workspace, board string) (string, error) {
+	var root string
+	err := tx.QueryRowContext(ctx, `SELECT root_id::text FROM canvas_model_canvases WHERE project=$1 AND workspace_id=$2 AND canvas_id=$3`, project, workspace, board).Scan(&root)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	return root, err
+}
+func loadCanvasModel(ctx context.Context, tx *sql.Tx, project, workspace, root string) (canvasModel, error) {
+	model := emptyModel(root)
+	rows, err := tx.QueryContext(ctx, `SELECT canvas_id::text,parent_canvas_id::text,entry_element_id,version,archived FROM canvas_model_canvases WHERE project=$1 AND workspace_id=$2 AND root_id=$3 ORDER BY canvas_id`, project, workspace, root)
+	if err != nil {
+		return model, err
+	}
+	for rows.Next() {
+		var canvas modelCanvas
+		var parent, entry sql.NullString
+		var version int64
+		var archived bool
+		if err = rows.Scan(&canvas.ID, &parent, &entry, &version, &archived); err != nil {
+			rows.Close()
+			return model, err
+		}
+		if parent.Valid {
+			canvas.Parent = &modelParent{CanvasID: parent.String, EntryElementID: entry.String}
+		}
+		model.Versions[canvas.ID] = version
+		if !archived {
+			model.Canvases[canvas.ID] = canvas
+		}
+	}
+	err = rows.Err()
+	rows.Close()
+	if err != nil {
+		return model, err
+	}
+	rows, err = tx.QueryContext(ctx, `SELECT element_id,record,deleted,deleted_incarnation FROM canvas_model_elements WHERE project=$1 AND workspace_id=$2 AND root_id=$3 ORDER BY element_id`, project, workspace, root)
+	if err != nil {
+		return model, err
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var id string
+		var raw json.RawMessage
+		var deleted bool
+		var dead int64
+		if err = rows.Scan(&id, &raw, &deleted, &dead); err != nil {
+			return model, err
+		}
+		if dead > 0 {
+			model.Tombstones[id] = dead
+		}
+		var element map[string]any
+		if err = json.Unmarshal(raw, &element); err != nil {
+			return model, err
+		}
+		if dead > 0 {
+			model.TombstoneOwners[id] = modelString(element["ownerCanvasId"])
+		}
+		if !deleted {
+			model.Elements[id] = element
+		} else {
+			model.DeadRecords[id] = element
+		}
+	}
+	if err = rows.Err(); err != nil {
+		return model, err
+	}
+	return model, validateCanvasModel(model)
+}
+
+// Only changed element rows are written. canvas_document is a compatibility
+// projection for internal AI readers, never the source of a canonical GET/replay.
+func (s *service) saveCanvasModel(r *http.Request, tx *sql.Tx, project, workspace, account string, before, after canvasModel, participants map[string]bool) error {
+	ctx := r.Context()
+	if err := invalidateCanonicalAIIdentities(r, tx, project, workspace, before, after); err != nil {
+		return err
+	}
+	if _, err := tx.ExecContext(ctx, `SELECT set_config('foundry.canonical_writer','on',true)`); err != nil {
+		return err
+	}
+	projection, err := projectCanvasModel(after)
+	if err != nil {
+		return err
+	}
+	for _, id := range sortedKeys(participants) {
+		canvas, active := after.Canvases[id]
+		if active {
+			if _, existed := before.Versions[id]; !existed {
+				title := "Canvas"
+				if canvas.Parent != nil {
+					data := after.Elements[canvas.Parent.EntryElementID]["data"].(map[string]any)
+					if value := modelString(data["title"]); value != "" {
+						title = value
+					}
+				}
+				if _, err = tx.ExecContext(ctx, `INSERT INTO materials(project,workspace_id,id,kind,title,created_by) VALUES($1,$2,$3,'board',$4,$5)`, project, workspace, id, title, account); err != nil {
+					return err
+				}
+			}
+			var parent, entry any
+			if canvas.Parent != nil {
+				parent, entry = canvas.Parent.CanvasID, canvas.Parent.EntryElementID
+			}
+			_, err = tx.ExecContext(ctx, `INSERT INTO canvas_model_canvases(project,workspace_id,root_id,canvas_id,parent_canvas_id,entry_element_id,version) VALUES($1,$2,$3,$4,$5,$6,$7) ON CONFLICT(project,workspace_id,canvas_id) DO UPDATE SET parent_canvas_id=EXCLUDED.parent_canvas_id,entry_element_id=EXCLUDED.entry_element_id,version=EXCLUDED.version,archived=false`, project, workspace, after.Root, id, parent, entry, after.Versions[id])
+		} else {
+			_, err = tx.ExecContext(ctx, `UPDATE canvas_model_canvases SET archived=true,version=$4 WHERE project=$1 AND workspace_id=$2 AND canvas_id=$3`, project, workspace, id, after.Versions[id])
+		}
+		if err != nil {
+			return err
+		}
+	}
+	for _, id := range sortedKeys(after.Elements) {
+		element := after.Elements[id]
+		if modelEqual(before.Elements[id], element) && before.Tombstones[id] == after.Tombstones[id] {
+			continue
+		}
+		raw, err := json.Marshal(element)
+		if err != nil {
+			return err
+		}
+		written, err := tx.ExecContext(ctx, `INSERT INTO canvas_model_elements(project,workspace_id,root_id,element_id,owner_canvas_id,incarnation,deleted_incarnation,record) VALUES($1,$2,$3,$4,$5,$6,$7,$8) ON CONFLICT(project,element_id) DO UPDATE SET owner_canvas_id=EXCLUDED.owner_canvas_id,incarnation=EXCLUDED.incarnation,deleted_incarnation=EXCLUDED.deleted_incarnation,record=EXCLUDED.record,deleted=false WHERE canvas_model_elements.workspace_id=EXCLUDED.workspace_id AND canvas_model_elements.root_id=EXCLUDED.root_id`, project, workspace, after.Root, id, element["ownerCanvasId"], modelInt(element["incarnation"]), after.Tombstones[id], raw)
+		if err != nil {
+			return err
+		}
+		if count, err := written.RowsAffected(); err != nil {
+			return err
+		} else if count != 1 {
+			return errModelConflict
+		}
+	}
+	for _, id := range sortedKeys(after.Tombstones) {
+		if after.Elements[id] != nil || before.Elements[id] == nil && before.Tombstones[id] == after.Tombstones[id] {
+			continue
+		}
+		record := after.DeadRecords[id]
+		if record == nil {
+			return errCanvasModel
+		}
+		raw, err := json.Marshal(record)
+		if err != nil {
+			return err
+		}
+		written, err := tx.ExecContext(ctx, `INSERT INTO canvas_model_elements(project,workspace_id,root_id,element_id,owner_canvas_id,incarnation,deleted_incarnation,record,deleted) VALUES($1,$2,$3,$4,$5,$6,$6,$7,true) ON CONFLICT(project,element_id) DO UPDATE SET owner_canvas_id=EXCLUDED.owner_canvas_id,incarnation=EXCLUDED.incarnation,deleted_incarnation=EXCLUDED.deleted_incarnation,record=EXCLUDED.record,deleted=true WHERE canvas_model_elements.workspace_id=EXCLUDED.workspace_id AND canvas_model_elements.root_id=EXCLUDED.root_id`, project, workspace, after.Root, id, record["ownerCanvasId"], after.Tombstones[id], raw)
+		if err != nil {
+			return err
+		}
+		if count, err := written.RowsAffected(); err != nil {
+			return err
+		} else if count != 1 {
+			return errModelConflict
+		}
+	}
+	// Archive relations first; parent/entry changes then install the final owning tree.
+	for _, id := range sortedKeys(participants) {
+		if id != after.Root {
+			if _, err = tx.ExecContext(ctx, `UPDATE canvas_subgraphs SET archived_at=now() WHERE project=$1 AND workspace_id=$2 AND child_board_id=$3`, project, workspace, id); err != nil {
+				return err
+			}
+		}
+	}
+	canvases := sortedKeys(after.Canvases)
+	sort.SliceStable(canvases, func(i, j int) bool {
+		a, _ := modelAncestors(after, canvases[i])
+		b, _ := modelAncestors(after, canvases[j])
+		return len(a) < len(b)
+	})
+	for _, id := range canvases {
+		canvas := after.Canvases[id]
+		if !participants[id] || canvas.Parent == nil {
+			continue
+		}
+		_, err = tx.ExecContext(ctx, `INSERT INTO canvas_subgraphs(project,workspace_id,parent_board_id,frame_id,child_board_id) VALUES($1,$2,$3,$4,$5) ON CONFLICT(project,workspace_id,child_board_id) DO UPDATE SET parent_board_id=EXCLUDED.parent_board_id,frame_id=EXCLUDED.frame_id,archived_at=NULL`, project, workspace, canvas.Parent.CanvasID, canvas.Parent.EntryElementID, id)
+		if err != nil {
+			return err
+		}
+	}
+	for _, id := range sortedKeys(participants) {
+		if _, active := after.Canvases[id]; !active {
+			_, err = tx.ExecContext(ctx, `UPDATE materials SET canvas_version=$4 WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, id, after.Versions[id])
+			if err != nil {
+				return err
+			}
+			continue
+		}
+		// Asset bindings still run through service checks; canonical identity
+		// invalidation has already run on the normalized before/after models.
+		if err = s.saveCanvas(r, tx, project, workspace, canvasSnapshot{BoardID: id, Version: after.Versions[id], Document: projection[id]}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func projectCanvasModel(model canvasModel) (map[string]json.RawMessage, error) {
+	documents := map[string]map[string]any{}
+	for id := range model.Canvases {
+		documents[id] = map[string]any{"schema_version": float64(2), "nodes": []any{}, "edges": []any{}, "viewport": map[string]any{"x": float64(0), "y": float64(0), "zoom": float64(1)}}
+	}
+	elements := sortedKeys(model.Elements)
+	sort.SliceStable(elements, func(i, j int) bool {
+		return modelString(model.Elements[elements[i]]["orderKey"]) < modelString(model.Elements[elements[j]]["orderKey"])
+	})
+	childByEntry := map[string]string{}
+	for id, canvas := range model.Canvases {
+		if canvas.Parent != nil {
+			childByEntry[canvas.Parent.EntryElementID] = id
+		}
+	}
+	for _, id := range elements {
+		element := model.Elements[id]
+		if element["structure"] != "node" {
+			continue
+		}
+		kind := modelString(element["componentId"])
+		if modelInt(element["dataVersion"]) != 1 || !canvasChoice(kind, "text", "script", "image", "plain-text", "plain-image", "icon", "frame") {
+			continue
+		}
+		data := map[string]any{}
+		for key, value := range element["data"].(map[string]any) {
+			data[key] = value
+		}
+		data["kind"] = kind
+		geometry := element["geometry"].(map[string]any)
+		data["rotation"] = geometry["rotation"]
+		typ := "material"
+		switch kind {
+		case "plain-text":
+			typ = "plainText"
+		case "plain-image":
+			typ = "plainImage"
+		case "icon":
+			typ = "icon"
+		case "frame":
+			typ = "frame"
+		}
+		if child := childByEntry[id]; child != "" {
+			data["subgraph"], data["ports"] = map[string]any{"boardId": child}, []any{}
+		}
+		node := map[string]any{"id": id, "type": typ, "position": map[string]any{"x": geometry["x"], "y": geometry["y"]}, "width": geometry["width"], "height": geometry["height"], "data": data}
+		owner := modelString(element["ownerCanvasId"])
+		documents[owner]["nodes"] = append(documents[owner]["nodes"].([]any), node)
+	}
+	for _, id := range elements {
+		element := model.Elements[id]
+		if element["structure"] != "connection" || element["componentId"] != "connection" || modelInt(element["dataVersion"]) != 1 {
+			continue
+		}
+		owner := modelString(element["ownerCanvasId"])
+		endpoints := []canvasConnectionEndpoint{}
+		skip := false
+		for index, field := range []string{"source", "target"} {
+			endpoint := element[field].(map[string]any)
+			node := model.Elements[modelString(endpoint["elementId"])]
+			board := modelString(node["ownerCanvasId"])
+			if connectionNode(documents[board], modelString(node["id"])) == nil {
+				skip = true
+				break
+			}
+			handle := modelString(endpoint["portId"])
+			if handle == "" {
+				handle = "left"
+				if index == 0 {
+					handle = "right"
+				}
+			}
+			path := []subgraphRelation{}
+			for next := board; next != owner; {
+				canvas := model.Canvases[next]
+				if canvas.Parent == nil {
+					return nil, errCanvasModel
+				}
+				path = append(path, subgraphRelation{Parent: canvas.Parent.CanvasID, Frame: canvas.Parent.EntryElementID, Child: next})
+				next = canvas.Parent.CanvasID
+			}
+			direction := "output"
+			if index == 1 {
+				direction = "input"
+			}
+			resolved, _, err := exposeConnectionEndpoint(canvasConnectionEndpoint{Board: board, Node: modelString(node["id"]), Handle: handle}, direction, path, documents)
+			// Direct frame/icon endpoints are canonical concepts; old AI readers cannot execute them.
+			if err != nil {
+				skip = true
+				break
+			}
+			endpoints = append(endpoints, resolved)
+		}
+		if skip {
+			continue
+		}
+		data := map[string]any{}
+		for key, value := range element["data"].(map[string]any) {
+			data[key] = value
+		}
+		if element["path"] != nil {
+			data["path"] = element["path"]
+		}
+		edge := map[string]any{"id": id, "source": endpoints[0].Node, "target": endpoints[1].Node, "sourceHandle": endpoints[0].Handle, "targetHandle": endpoints[1].Handle, "data": data}
+		documents[owner]["edges"] = append(documents[owner]["edges"].([]any), edge)
+	}
+	result := map[string]json.RawMessage{}
+	for id, document := range documents {
+		raw, err := json.Marshal(document)
+		if err != nil {
+			return nil, err
+		}
+		result[id] = raw
+	}
+	return result, nil
+}

internal/platform/canvas_model_stream.go

@@ -0,0 +1,111 @@
+package platform
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+)
+
+const modelStreamType = "application/vnd.foundry.canvas-model+ndjson;version=1"
+
+// The caller captures a coherent model while holding the workspace lock, then
+// releases its transaction before writing. A slow reader must not hold a writer.
+// This streams transfer/encoding; it does not stream database row acquisition.
+func writeCanvasModelStream(ctx context.Context, w http.ResponseWriter, model canvasModel) {
+	token := newModelID()
+	if token == "" {
+		reject(w, 500, "model_stream_unavailable")
+		return
+	}
+	view := model.view(nil)
+	// A count covers direct members only; an empty canvas is explicit too.
+	counts := map[string]int{}
+	owners := map[string]string{}
+	for _, canvas := range view.Canvases {
+		counts[canvas.ID] = 0
+	}
+	for _, element := range view.Elements {
+		owner := modelString(element["ownerCanvasId"])
+		if _, ok := counts[owner]; !ok {
+			reject(w, 500, "invalid_model_coverage")
+			return
+		}
+		id := modelString(element["id"])
+		if id == "" || owners[id] != "" {
+			reject(w, 500, "invalid_model_identity")
+			return
+		}
+		owners[id] = owner
+		counts[owner]++
+	}
+	header := response{"streamVersion": 1, "kind": "header", "sequence": 0, "snapshotToken": token,
+		"documentFormatVersion": canvasModelFormat, "projectId": model.Root, "canvases": view.Canvases,
+		"versions": view.Versions, "tombstones": view.Tombstones, "removedCanvasIds": view.Removed, "elementCount": len(view.Elements), "canvasElementCounts": counts, "elementOwners": owners}
+	const maxLine = 8 * 1024 * 1024
+	const maxBytes = 64 * 1024 * 1024
+	sequence, total := 0, 0
+	started := false
+	write := func(value response) bool {
+		if ctx.Err() != nil {
+			return false
+		}
+		raw, err := json.Marshal(value)
+		if err != nil || len(raw) > maxLine || total+len(raw)+1 > maxBytes || sequence >= 4096 {
+			if !started {
+				reject(w, 413, "model_stream_budget")
+			}
+			return false
+		}
+		if !started {
+			w.Header().Set("Content-Type", modelStreamType)
+			w.Header().Set("Cache-Control", "no-store")
+			w.Header().Add("Vary", "Accept")
+			w.Header().Set("X-Content-Type-Options", "nosniff")
+			w.WriteHeader(http.StatusOK)
+			started = true
+		}
+		total += len(raw) + 1
+		if n, writeErr := w.Write(append(raw, '\n')); writeErr != nil || n != len(raw)+1 {
+			return false
+		}
+		sequence++
+		// A missing terminal record is an explicit incomplete stream at the client.
+		// Never append an unrelated JSON error after streaming has begun.
+		return http.NewResponseController(w).Flush() == nil
+	}
+	if !write(header) {
+		return
+	}
+	batch := []map[string]any{}
+	batchBytes := 0
+	flush := func() bool {
+		if len(batch) == 0 {
+			return true
+		}
+		if !write(response{"streamVersion": 1, "kind": "elements", "sequence": sequence, "snapshotToken": token, "elements": batch}) {
+			return false
+		}
+		batch, batchBytes = []map[string]any{}, 0
+		return true
+	}
+	for _, element := range view.Elements {
+		if ctx.Err() != nil {
+			return
+		}
+		raw, err := json.Marshal(element)
+		if err != nil {
+			return
+		}
+		if len(batch) > 0 && (len(batch) == 64 || batchBytes+len(raw) > 512*1024) {
+			if !flush() {
+				return
+			}
+		}
+		batch = append(batch, element)
+		batchBytes += len(raw)
+	}
+	if !flush() {
+		return
+	}
+	write(response{"streamVersion": 1, "kind": "complete", "sequence": sequence, "snapshotToken": token, "elementCount": len(view.Elements)})
+}

internal/platform/canvas_model_stream_test.go

@@ -0,0 +1,137 @@
+package platform
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http/httptest"
+	"testing"
+)
+
+func streamRecords(t *testing.T, writer *httptest.ResponseRecorder) []response {
+	t.Helper()
+	var records []response
+	scanner := bufio.NewScanner(writer.Body)
+	for scanner.Scan() {
+		var record response
+		if err := json.Unmarshal(scanner.Bytes(), &record); err != nil {
+			t.Fatal(err)
+		}
+		records = append(records, record)
+	}
+	if err := scanner.Err(); err != nil {
+		t.Fatal(err)
+	}
+	return records
+}
+func TestCanonicalModelStreamFramesAndSnapshot(t *testing.T) {
+	model := modelTestDocument()
+	for i := 0; i < 129; i++ {
+		id := fmt.Sprintf("extra-%03d", i)
+		model.Elements[id] = modelTestNode(id, modelRootID)
+	}
+	model.Tombstones["deleted"] = 2
+	model.TombstoneOwners["deleted"] = modelRootID
+	writer := httptest.NewRecorder()
+	writeCanvasModelStream(context.Background(), writer, model)
+	if writer.Code != 200 || writer.Header().Get("Content-Type") != modelStreamType || !writer.Flushed {
+		t.Fatal("stream was not negotiated/flushed", writer.Code, writer.Header())
+	}
+	records := streamRecords(t, writer)
+	if len(records) != 5 || records[0]["kind"] != "header" || records[4]["kind"] != "complete" {
+		t.Fatal("missing stream framing", len(records))
+	}
+	token := modelString(records[0]["snapshotToken"])
+	if !uuidSlugPattern.MatchString(token) || records[0]["projectId"] != modelRootID || !modelEqual(records[0]["versions"], model.Versions) || !modelEqual(records[0]["tombstones"], model.Tombstones) {
+		t.Fatal("stream header lost snapshot identity")
+	}
+	owners := records[0]["elementOwners"].(map[string]any)
+	if len(owners) != len(model.Elements) {
+		t.Fatal("identity manifest must cover unloaded elements too")
+	}
+	for id, element := range model.Elements {
+		if owners[id] != element["ownerCanvasId"] {
+			t.Fatal("identity manifest mixed owners", id)
+		}
+	}
+	seen := map[string]bool{}
+	for i, record := range records {
+		if record["sequence"] != float64(i) || record["snapshotToken"] != token || record["streamVersion"] != float64(1) {
+			t.Fatal("mixed or unordered snapshot")
+		}
+		if record["kind"] == "elements" {
+			items := record["elements"].([]any)
+			if len(items) == 0 || len(items) > 64 {
+				t.Fatal("unbounded record batch")
+			}
+			for _, item := range items {
+				element := item.(map[string]any)
+				id := modelString(element["id"])
+				if seen[id] || !modelEqual(element, model.Elements[id]) {
+					t.Fatal("duplicated or corrupted stream element")
+				}
+				seen[id] = true
+			}
+		}
+	}
+	if len(seen) != len(model.Elements) || records[4]["elementCount"] != float64(len(seen)) {
+		t.Fatal("terminal coverage mismatch")
+	}
+}
+
+type cancelStreamWriter struct {
+	*httptest.ResponseRecorder
+	cancel context.CancelFunc
+}
+
+func (writer cancelStreamWriter) Flush() {
+	writer.ResponseRecorder.Flush()
+	writer.cancel()
+}
+func TestCanonicalModelStreamCancellationNeverClaimsCompletion(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	writer := httptest.NewRecorder()
+	writeCanvasModelStream(ctx, cancelStreamWriter{writer, cancel}, modelTestDocument())
+	records := streamRecords(t, writer)
+	if len(records) != 1 || records[0]["kind"] != "header" {
+		t.Fatal("cancelled stream wrote a tail", len(records))
+	}
+}
+
+func TestCanonicalModelStreamDeclaresDirectScopeCountsIncludingEmptyCanvases(t *testing.T) {
+	model := modelTestDocument()
+	empty, nested := modelTestID(41), modelTestID(42)
+	model.Canvases[empty] = modelCanvas{ID: empty, Parent: &modelParent{CanvasID: model.Root, EntryElementID: "frame-empty"}}
+	model.Canvases[nested] = modelCanvas{ID: nested, Parent: &modelParent{CanvasID: model.Root, EntryElementID: "frame-nested"}}
+	model.Versions[empty], model.Versions[nested] = 1, 1
+	model.Elements["frame-empty"] = modelTestNode("frame-empty", model.Root)
+	model.Elements["frame-nested"] = modelTestNode("frame-nested", model.Root)
+	model.Elements["nested-node"] = modelTestNode("nested-node", nested)
+	writer := httptest.NewRecorder()
+	writeCanvasModelStream(context.Background(), writer, model)
+	records := streamRecords(t, writer)
+	if !modelEqual(records[0]["canvasElementCounts"], map[string]int{model.Root: 3, empty: 0, nested: 1}) {
+		t.Fatal("scope counts must count direct members, preserve empty scopes and match the captured snapshot")
+	}
+	bad := modelTestDocument()
+	bad.Elements["a"]["ownerCanvasId"] = "foreign"
+	failed := httptest.NewRecorder()
+	writeCanvasModelStream(context.Background(), failed, bad)
+	if failed.Code != 500 || failed.Flushed {
+		t.Fatal("invalid owner must fail before publishing a scope certificate")
+	}
+}
+
+func TestCanonicalModelStreamRejectsAmbiguousIdentityManifest(t *testing.T) {
+	for _, id := range []string{"", "a"} {
+		model := modelTestDocument()
+		model.Elements["other"] = modelTestNode(id, modelRootID)
+		writer := httptest.NewRecorder()
+		writeCanvasModelStream(context.Background(), writer, model)
+		if writer.Code != 500 || writer.Flushed {
+			t.Fatal("ambiguous identity was published before rejection")
+		}
+	}
+}

internal/platform/canvas_model_test.go

@@ -0,0 +1,244 @@
+package platform
+
+import (
+	"bytes"
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"testing"
+)
+
+const modelRootID = "10000000-0000-4000-8000-000000000001"
+const modelChildID = "10000000-0000-4000-8000-000000000002"
+const modelLegacyFrame = `{"id":"f","type":"frame","position":{"x":100,"y":200},"width":640,"height":400,"data":{"kind":"frame","title":"Partition","text":"","labelMode":"fixed"}}`
+
+// The schema runner mounts only the test binary, not the source tree.
+//
+//go:embed testdata/foundry-model-operation-v2.json
+var canonicalFrontendFixture []byte
+
+func modelJSON(value any) json.RawMessage { raw, _ := json.Marshal(value); return raw }
+func modelTestID(n int) string            { return fmt.Sprintf("90000000-0000-4000-8000-%012d", n) }
+func modelTestAllocator() func() string {
+	next := 0
+	return func() string { next++; return modelTestID(next) }
+}
+func modelTestNode(id, owner string) map[string]any {
+	return map[string]any{"id": id, "incarnation": float64(1), "ownerCanvasId": owner, "componentId": "text", "dataVersion": float64(1), "structure": "node", "data": map[string]any{"title": id, "text": "preserved"}, "geometry": map[string]any{"x": float64(0), "y": float64(0), "width": float64(260), "height": float64(200), "rotation": float64(0)}}
+}
+func modelTestDocument() canvasModel {
+	model := emptyModel(modelRootID)
+	model.Canvases[modelRootID] = modelCanvas{ID: modelRootID}
+	model.Versions[modelRootID] = 1
+	model.Elements["a"] = modelTestNode("a", modelRootID)
+	return model
+}
+
+func TestCanonicalFramesRetainRotationAcrossOwnerChanges(t *testing.T) {
+	model := modelTestDocument()
+	frame := modelTestNode("f", modelRootID)
+	frame["componentId"] = "frame"
+	frame["geometry"].(map[string]any)["rotation"] = float64(30)
+	model.Elements["f"] = frame
+	model.Canvases[modelChildID] = modelCanvas{ID: modelChildID, Parent: &modelParent{CanvasID: modelRootID, EntryElementID: "f"}}
+	model.Versions[modelChildID] = 1
+	member := modelTestNode("nested-frame", modelChildID)
+	member["componentId"] = "frame"
+	model.Elements["nested-frame"] = member
+	if err := validateCanvasModel(model); err != nil {
+		t.Fatalf("valid canonical frame rotation rejected: %v", err)
+	}
+	geometry := member["geometry"].(map[string]any)
+	moved := map[string]any{"x": float64(100), "y": float64(80), "width": float64(520), "height": float64(400), "rotation": float64(30)}
+	after, touched, err := applyModelOperations(model, []modelOperation{{ID: modelTestID(80), Changes: []modelChange{
+		{Kind: "field", Target: modelTarget{ID: "nested-frame", Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(modelChildID), After: modelJSON(modelRootID)},
+		{Kind: "field", Target: modelTarget{ID: "nested-frame", Incarnation: 1}, Field: "geometry", Before: modelJSON(geometry), After: modelJSON(moved)},
+	}}})
+	if err != nil || !touched[modelRootID] || !touched[modelChildID] {
+		t.Fatalf("rotated frame owner change failed: %v", err)
+	}
+	if after.Elements["nested-frame"]["ownerCanvasId"] != modelRootID || !modelEqual(after.Elements["nested-frame"]["geometry"], moved) || model.Elements["nested-frame"]["ownerCanvasId"] != modelChildID {
+		t.Fatal("owner change lost geometry or changed the source model")
+	}
+	projection, err := projectCanvasModel(after)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var document map[string]any
+	if err := json.Unmarshal(projection[modelRootID], &document); err != nil {
+		t.Fatal(err)
+	}
+	rotated := 0
+	for _, raw := range document["nodes"].([]any) {
+		node := raw.(map[string]any)
+		if node["id"] != "f" && node["id"] != "nested-frame" {
+			continue
+		}
+		rotated++
+		if node["data"].(map[string]any)["rotation"] != float64(30) {
+			t.Fatal("reader projection erased canonical rotation")
+		}
+	}
+	if rotated != 2 {
+		t.Fatal("reader projection omitted a rotated frame")
+	}
+	patched, err := prepareModelAIPatch(after, modelRootID, "a", response{"text": "new text"})
+	if err != nil || patched.Elements["f"]["geometry"].(map[string]any)["rotation"] != float64(30) {
+		t.Fatalf("unrelated canonical AI patch rejected or rewound rotation: %v", err)
+	}
+	bad := cloneModel(after)
+	bad.Elements["f"]["geometry"].(map[string]any)["rotation"] = float64(360)
+	if validateCanvasModel(bad) == nil {
+		t.Fatal("out-of-range canonical rotation accepted")
+	}
+	legacy := json.RawMessage(`{"schema_version":1,"nodes":[{"id":"f","type":"frame","position":{"x":0,"y":0},"width":640,"height":400,"data":{"kind":"frame","title":"F","text":"","rotation":30}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`)
+	if _, valid := normalizeCanvas(legacy); valid {
+		t.Fatal("canonical support changed the legacy snapshot write contract")
+	}
+}
+
+func TestCanonicalMigrationResolvesCanvasLocalIdentitiesAndPorts(t *testing.T) {
+	root := `{"schema_version":2,"nodes":[{"id":"a","type":"plainText","position":{"x":0,"y":0},"width":240,"height":72,"data":{"kind":"plain-text","title":"parent","text":""}},{"id":"f","type":"frame","position":{"x":100,"y":200},"width":640,"height":400,"data":{"kind":"frame","title":"F","text":"","subgraph":{"boardId":"` + modelChildID + `"},"ports":[{"id":"p","nodeId":"a","handle":"right","direction":"output"}]}}],"edges":[{"id":"e","source":"f","sourceHandle":"port:p","target":"a","targetHandle":"left"}],"viewport":{"x":0,"y":0,"zoom":1}}`
+	child := `{"schema_version":2,"nodes":[{"id":"a","type":"plainText","position":{"x":10,"y":20},"width":240,"height":72,"data":{"kind":"plain-text","title":"child","text":""}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`
+	snapshots := map[string]canvasSnapshot{modelRootID: {BoardID: modelRootID, Version: 3, Document: json.RawMessage(root)}, modelChildID: {BoardID: modelChildID, Version: 7, Document: json.RawMessage(child)}}
+	result, err := migrateCanvasModel(modelRootID, snapshots, []subgraphRelation{{Parent: modelRootID, Frame: "f", Child: modelChildID}}, modelTestAllocator())
+	if err != nil {
+		t.Fatal(err)
+	}
+	ids := map[string]string{}
+	for _, mapping := range result.Identities {
+		ids[mapping.SourceCanvasID+"/"+mapping.Structure+"/"+mapping.SourceID] = mapping.ElementID
+	}
+	parentA, childA := ids[modelRootID+"/node/a"], ids[modelChildID+"/node/a"]
+	if parentA == childA || parentA == "" || childA == "" {
+		t.Fatal("canvas-local node IDs were merged")
+	}
+	edge := result.Model.Elements[ids[modelRootID+"/connection/e"]]
+	if edge["source"].(map[string]any)["elementId"] != childA || edge["target"].(map[string]any)["elementId"] != parentA || edge["ownerCanvasId"] != modelRootID {
+		t.Fatal("logical endpoint or common ancestor owner was lost")
+	}
+	if result.Model.Canvases[modelChildID].Parent.EntryElementID != ids[modelRootID+"/node/f"] || result.Model.Versions[modelRootID] != 4 || result.Model.Versions[modelChildID] != 8 {
+		t.Fatal("migration did not publish an identity/version barrier")
+	}
+	if string(snapshots[modelRootID].Document) != root || string(snapshots[modelChildID].Document) != child {
+		t.Fatal("migration mutated source snapshots")
+	}
+	projection, err := projectCanvasModel(result.Model)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, raw := range projection {
+		if _, valid := normalizeCanvas(raw); !valid {
+			t.Fatalf("invalid compatibility projection: %s", raw)
+		}
+	}
+}
+func TestCanonicalMigrationTurnsImplicitFramesIntoOwningCanvases(t *testing.T) {
+	root := `{"schema_version":1,"nodes":[` + modelLegacyFrame + `,{"id":"a","type":"plainText","position":{"x":150,"y":260},"width":240,"height":72,"data":{"kind":"plain-text","title":"a","text":"","frameId":"f"}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`
+	result, err := migrateCanvasModel(modelRootID, map[string]canvasSnapshot{modelRootID: {BoardID: modelRootID, Version: 1, Document: json.RawMessage(root)}}, nil, modelTestAllocator())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(result.NewCanvases) != 1 || len(result.Model.Canvases) != 2 {
+		t.Fatal("legacy partition was not given a canvas")
+	}
+	var node map[string]any
+	for _, mapping := range result.Identities {
+		if mapping.SourceID == "a" {
+			node = result.Model.Elements[mapping.ElementID]
+		}
+	}
+	geometry := node["geometry"].(map[string]any)
+	if node["ownerCanvasId"] != result.NewCanvases[0] || geometry["x"] != float64(26) || geometry["y"] != float64(24) {
+		t.Fatal("membership or owner-local geometry changed")
+	}
+	if _, exists := node["data"].(map[string]any)["frameId"]; exists {
+		t.Fatal("second ownership fact leaked into canonical data")
+	}
+}
+func TestCanonicalOperationsPreserveOpaquePayloadAndStableMoveIdentity(t *testing.T) {
+	model := modelTestDocument()
+	frame := modelTestNode("f", modelRootID)
+	frame["componentId"] = "frame"
+	model.Elements["f"] = frame
+	model.Canvases[modelChildID] = modelCanvas{ID: modelChildID, Parent: &modelParent{CanvasID: modelRootID, EntryElementID: "f"}}
+	model.Versions[modelChildID] = 1
+	future := modelTestNode("future", modelRootID)
+	future["componentId"], future["dataVersion"], future["data"], future["futureEnvelope"] = "plugin.future", float64(42), map[string]any{"nested": map[string]any{"list": []any{"x", float64(2)}}}, map[string]any{"retain": true}
+	future["data"].(map[string]any)["constructor"] = map[string]any{"retain": true}
+	future["data"].(map[string]any)["__proto__"] = map[string]any{"ordinary": "JSON data"}
+	model.Elements["future"] = future
+	op := modelOperation{ID: modelTestID(1), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: "a", Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(modelRootID), After: modelJSON(modelChildID)}}}
+	after, touched, err := applyModelOperations(model, []modelOperation{op})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if after.Elements["a"]["id"] != "a" || after.Elements["a"]["ownerCanvasId"] != modelChildID || !touched[modelRootID] || !touched[modelChildID] {
+		t.Fatal("move changed identity or omitted a participant")
+	}
+	if !modelEqual(after.Elements["future"], future) || model.Elements["a"]["ownerCanvasId"] != modelRootID {
+		t.Fatal("opaque payload or old snapshot was mutated")
+	}
+}
+func TestCanonicalDeleteRestoreRejectsOldIncarnation(t *testing.T) {
+	model := modelTestDocument()
+	deleted, _, err := applyModelOperations(model, []modelOperation{{ID: modelTestID(1), Changes: []modelChange{{Kind: "element", ID: "a", Before: modelJSON(model.Elements["a"]), After: modelJSON(nil)}}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if deleted.Tombstones["a"] != 1 {
+		t.Fatal("missing tombstone")
+	}
+	restored := modelTestNode("a", modelRootID)
+	restored["incarnation"] = float64(2)
+	live, _, err := applyModelOperations(deleted, []modelOperation{{ID: modelTestID(2), Changes: []modelChange{{Kind: "element", ID: "a", Before: modelJSON(nil), After: modelJSON(restored)}}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _, err = applyModelOperations(live, []modelOperation{{ID: modelTestID(3), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: "a", Incarnation: 1}, Field: "data.title", Before: modelJSON("a"), After: modelJSON("stale")}}}})
+	if err != errModelConflict || live.Elements["a"]["data"].(map[string]any)["title"] != "a" {
+		t.Fatal("old callback claimed the restored incarnation")
+	}
+}
+func TestCanonicalValidationRejectsPartialChangesAndWrongEdgeOwner(t *testing.T) {
+	model := modelTestDocument()
+	before := modelJSON(model)
+	operations := []modelOperation{{ID: modelTestID(1), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: "a", Incarnation: 1}, Field: "data.title", Before: modelJSON("a"), After: modelJSON("changed")}, {Kind: "field", Target: modelTarget{ID: "missing", Incarnation: 1}, Field: "geometry", Before: modelJSON(nil), After: modelJSON(nil)}}}}
+	if _, _, err := applyModelOperations(model, operations); err == nil {
+		t.Fatal("invalid second change was accepted")
+	}
+	if string(modelJSON(model)) != string(before) {
+		t.Fatal("failed batch changed the source")
+	}
+	frame := modelTestNode("f", modelRootID)
+	frame["componentId"] = "frame"
+	model.Elements["f"] = frame
+	model.Canvases[modelChildID] = modelCanvas{ID: modelChildID, Parent: &modelParent{CanvasID: modelRootID, EntryElementID: "f"}}
+	model.Versions[modelChildID] = 1
+	model.Elements["child"] = modelTestNode("child", modelChildID)
+	model.Elements["e"] = map[string]any{"id": "e", "ownerCanvasId": modelChildID, "incarnation": float64(1), "componentId": "connection", "dataVersion": float64(1), "structure": "connection", "data": map[string]any{}, "source": map[string]any{"elementId": "a"}, "target": map[string]any{"elementId": "child"}, "path": nil}
+	if validateCanvasModel(model) == nil {
+		t.Fatal("cross-child connection acquired a child owner")
+	}
+}
+
+func TestCanonicalFrontendProtocolFixture(t *testing.T) {
+	var input modelBatch
+	decoder := json.NewDecoder(bytes.NewReader(canonicalFrontendFixture))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&input); err != nil {
+		t.Fatal(err)
+	}
+	if input.ProtocolVersion != canvasModelProtocol || !uuidSlugPattern.MatchString(input.RequestID) || input.Expected[modelRootID] != 3 {
+		t.Fatal("frontend fixture envelope is incompatible")
+	}
+	before := modelTestDocument()
+	before.Versions[modelRootID] = 3
+	after, touched, err := applyModelOperations(before, input.Operations)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !touched[modelRootID] || after.Versions[modelRootID] != 4 || after.Elements["a"]["data"].(map[string]any)["title"] != "renamed" || after.Elements["a"]["data"].(map[string]any)["text"] != "preserved" {
+		t.Fatal("frontend fixture did not apply exactly its intended field change")
+	}
+}

internal/platform/canvas_operations.go

@@ -0,0 +1,147 @@
+package platform
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+)
+
+const canvasOperationsProtocol = 1
+
+type canvasOperation struct {
+	ID        string                     `json:"id"`
+	Type      string                     `json:"type"`
+	CanvasID  string                     `json:"canvas_id"`
+	ElementID string                     `json:"element_id"`
+	Record    json.RawMessage            `json:"record,omitempty"`
+	Patch     map[string]json.RawMessage `json:"patch,omitempty"`
+}
+type canvasOperationBatch struct {
+	ProtocolVersion  int               `json:"protocol_version"`
+	RequestID        string            `json:"request_id"`
+	ExpectedVersions map[string]int64  `json:"expected_versions"`
+	Operations       []canvasOperation `json:"operations"`
+}
+
+var errInvalidCanvasOperation = errors.New("invalid_canvas_operation")
+
+// applyCanvasOperations stages a complete batch. Input snapshots are never mutated.
+// HTTP/auth/version/idempotency are checked by the transaction coordinator.
+func applyCanvasOperations(initial map[string]canvasSnapshot, operations []canvasOperation) (map[string]canvasSnapshot, error) {
+	if len(operations) == 0 || len(operations) > 2500 {
+		return nil, errInvalidCanvasOperation
+	}
+	documents := make(map[string]map[string]json.RawMessage, len(initial))
+	for id, snapshot := range initial {
+		var document map[string]json.RawMessage
+		if json.Unmarshal(snapshot.Document, &document) != nil {
+			return nil, errInvalidCanvasOperation
+		}
+		documents[id] = document
+	}
+	seen := map[string]bool{}
+	for _, operation := range operations {
+		if !uuidSlugPattern.MatchString(operation.ID) || seen[operation.ID] || !canvasID.MatchString(operation.ElementID) {
+			return nil, errInvalidCanvasOperation
+		}
+		seen[operation.ID] = true
+		document := documents[operation.CanvasID]
+		if document == nil {
+			return nil, errInvalidCanvasOperation
+		}
+		collection := ""
+		switch operation.Type {
+		case "node.create", "node.patch", "node.delete":
+			collection = "nodes"
+		case "edge.create", "edge.patch", "edge.delete":
+			collection = "edges"
+		default:
+			return nil, errInvalidCanvasOperation
+		}
+		var records []map[string]json.RawMessage
+		if json.Unmarshal(document[collection], &records) != nil {
+			return nil, errInvalidCanvasOperation
+		}
+		index := -1
+		for i, record := range records {
+			var id string
+			_ = json.Unmarshal(record["id"], &id)
+			if id == operation.ElementID {
+				index = i
+				break
+			}
+		}
+		switch operation.Type {
+		case "node.create", "edge.create":
+			if index >= 0 || len(operation.Record) == 0 || len(operation.Patch) != 0 {
+				return nil, fmt.Errorf("%w: create conflict", errInvalidCanvasOperation)
+			}
+			var record map[string]json.RawMessage
+			var id string
+			if json.Unmarshal(operation.Record, &record) != nil || json.Unmarshal(record["id"], &id) != nil || id != operation.ElementID {
+				return nil, errInvalidCanvasOperation
+			}
+			records = append(records, record)
+		case "node.delete", "edge.delete":
+			if index < 0 || len(operation.Record) != 0 || len(operation.Patch) != 0 {
+				return nil, fmt.Errorf("%w: missing delete target", errInvalidCanvasOperation)
+			}
+			records = append(records[:index], records[index+1:]...)
+		case "node.patch", "edge.patch":
+			if index < 0 || len(operation.Record) != 0 || len(operation.Patch) == 0 {
+				return nil, errInvalidCanvasOperation
+			}
+			for field, value := range operation.Patch {
+				allowed := field == "data" || collection == "nodes" && (field == "position" || field == "width" || field == "height") || collection == "edges" && (field == "source" || field == "target" || field == "sourceHandle" || field == "targetHandle")
+				if !allowed {
+					return nil, errInvalidCanvasOperation
+				}
+				if field == "data" {
+					// Merge individual data fields; a geometry-only patch never rolls back titles/assets.
+					var before, patch map[string]json.RawMessage
+					if json.Unmarshal(records[index][field], &before) != nil || json.Unmarshal(value, &patch) != nil || patch == nil {
+						return nil, errInvalidCanvasOperation
+					}
+					if before == nil {
+						before = map[string]json.RawMessage{}
+					}
+					for key, item := range patch {
+						if string(item) == "null" {
+							delete(before, key)
+						} else {
+							before[key] = item
+						}
+					}
+					encoded, err := json.Marshal(before)
+					if err != nil {
+						return nil, err
+					}
+					records[index][field] = encoded
+				} else {
+					records[index][field] = append(json.RawMessage(nil), value...)
+				}
+			}
+		}
+		encoded, err := json.Marshal(records)
+		if err != nil {
+			return nil, err
+		}
+		document[collection] = encoded
+	}
+	result := make(map[string]canvasSnapshot, len(initial))
+	for id, document := range documents {
+		raw, err := json.Marshal(document)
+		if err != nil {
+			return nil, err
+		}
+		normalized, valid := normalizeCanvas(raw)
+		if !valid {
+			return nil, errInvalidCanvasOperation
+		}
+		snapshot := initial[id]
+		snapshot.Document = normalized
+		snapshot.Version++
+		result[id] = snapshot
+	}
+	return result, nil
+}

internal/platform/canvas_operations_http.go

@@ -0,0 +1,218 @@
+package platform
+
+import (
+	"database/sql"
+	"encoding/json"
+	"io"
+	"net/http"
+	"sort"
+	"time"
+)
+
+const canvasOperationsAction = "headless.operations.v1"
+
+func (s *service) submitCanvasOperations(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodPost {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	if !acceptsCanvasV2(r) {
+		reject(w, 409, "canvas_schema_upgrade_required")
+		return nil
+	}
+	key := canvasIdempotencyKey(r)
+	if !uuidSlugPattern.MatchString(key) {
+		reject(w, 400, "invalid_idempotency_key")
+		return nil
+	}
+	var input canvasOperationBatch
+	decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, canvasLimit))
+	decoder.DisallowUnknownFields()
+	if decoder.Decode(&input) != nil || decoder.Decode(new(any)) != io.EOF || input.ProtocolVersion != canvasOperationsProtocol || input.RequestID != key || len(input.Operations) == 0 || len(input.Operations) > 2500 || len(input.ExpectedVersions) == 0 || len(input.ExpectedVersions) > 64 {
+		reject(w, 400, "invalid_canvas_operation_batch")
+		return nil
+	}
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	if _, ok := input.ExpectedVersions[board]; !ok {
+		reject(w, 428, "version_required")
+		return nil
+	}
+	participants := make([]string, 0, len(input.ExpectedVersions))
+	for id, version := range input.ExpectedVersions {
+		if !uuidSlugPattern.MatchString(id) || version < 1 {
+			reject(w, 400, "invalid_canvas_operation_batch")
+			return nil
+		}
+		participants = append(participants, id)
+	}
+	for _, operation := range input.Operations {
+		if _, ok := input.ExpectedVersions[operation.CanvasID]; !ok {
+			reject(w, 428, "version_required")
+			return nil
+		}
+	}
+	sort.Strings(participants)
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	// lockMaterial serializes the workspace; sorted participants preserve a stable lock order.
+	for _, id := range participants {
+		kind, role, e := lockMaterial(r.Context(), tx, project, workspace, id, account)
+		if e != nil {
+			return e
+		}
+		if kind != "board" {
+			reject(w, 400, "invalid_material")
+			return nil
+		}
+		if role == "viewer" {
+			reject(w, 403, "forbidden")
+			return nil
+		}
+	}
+	// Resolve the same request before comparing expected versions: exact retry after lost ACK succeeds.
+	done, err := transactionRetry(w, r, tx, project, account, board, canvasOperationsAction, key, payloadDigest(input))
+	if err != nil {
+		return err
+	}
+	if done {
+		return nil
+	}
+	before := make([]canvasSnapshot, 0, len(participants))
+	initial := map[string]canvasSnapshot{}
+	for _, id := range participants {
+		snapshot, e := loadCanvas(r, tx, project, workspace, id)
+		if e != nil {
+			return e
+		}
+		if snapshot.Version != input.ExpectedVersions[id] {
+			return commitCanvasOperationReceipt(w, r, tx, project, account, board, input, 412, response{"error": "version_conflict", "status": "not-applied", "terminal": true, "request_id": key}, nil, nil)
+		}
+		initial[id] = snapshot
+		before = append(before, snapshot)
+	}
+	staged, err := applyCanvasOperations(initial, input.Operations)
+	if err != nil {
+		return commitCanvasOperationReceipt(w, r, tx, project, account, board, input, 400, response{"error": "invalid_canvas_operation", "status": "not-applied", "terminal": true, "request_id": key}, nil, nil)
+	}
+	snapshots := make([]canvasSnapshot, 0, len(participants))
+	versions := map[string]int64{}
+	// Validate all participant documents before writing any of them.
+	for _, id := range participants {
+		snapshot := staged[id]
+		valid, e := validateCanvasRelations(r, tx, project, workspace, id, initial[id].Document, snapshot.Document)
+		if e != nil {
+			return e
+		}
+		if !valid {
+			return commitCanvasOperationReceipt(w, r, tx, project, account, board, input, 409, response{"error": "ownership_conflict", "status": "not-applied", "terminal": true, "request_id": key}, nil, nil)
+		}
+		if !s.validateCanvasAIModels(w, r, snapshot.Document) {
+			return nil
+		}
+		valid, e = s.validateCanvasAssets(r, tx, project, workspace, account, snapshot.Document)
+		if e != nil {
+			return e
+		}
+		if !valid {
+			return commitCanvasOperationReceipt(w, r, tx, project, account, board, input, 400, response{"error": "invalid_asset_reference", "status": "not-applied", "terminal": true, "request_id": key}, nil, nil)
+		}
+		snapshots = append(snapshots, snapshot)
+		versions[id] = snapshot.Version
+	}
+	for _, snapshot := range snapshots {
+		if err = s.saveCanvas(r, tx, project, workspace, snapshot); err != nil {
+			return err
+		}
+	}
+	operationIDs := make([]string, 0, len(input.Operations))
+	for _, operation := range input.Operations {
+		operationIDs = append(operationIDs, operation.ID)
+	}
+	body := response{"protocol_version": canvasOperationsProtocol, "status": "applied", "request_id": key, "operation_ids": operationIDs, "snapshots": snapshots, "applied_versions": versions, "parent": staged[board]}
+	return commitCanvasOperationReceipt(w, r, tx, project, account, board, input, 200, body, before, versions)
+}
+
+// A terminal rejection also reserves the frozen key/body. Losing that response must
+// not turn a definite zero-write result into a future execution of the same request.
+func commitCanvasOperationReceipt(w http.ResponseWriter, r *http.Request, tx *sql.Tx, project, account, board string, input canvasOperationBatch, status int, body response, before []canvasSnapshot, versions map[string]int64) error {
+	var transactionID string
+	if err := tx.QueryRowContext(r.Context(), `SELECT gen_random_uuid()::text`).Scan(&transactionID); err != nil {
+		return err
+	}
+	body["transaction_id"] = transactionID
+	body["protocol_version"] = canvasOperationsProtocol
+	expires := time.Now().Add(7 * 24 * time.Hour)
+	bodyRaw, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	beforeRaw, err := json.Marshal(before)
+	if err != nil {
+		return err
+	}
+	versionsRaw, err := json.Marshal(versions)
+	if err != nil {
+		return err
+	}
+	_, err = tx.ExecContext(r.Context(), `INSERT INTO canvas_transactions(project,workspace_id,board_id,id,account_id,action,idempotency_key,payload_hash,response_status,response_body,before_state,after_versions,expires_at) VALUES($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13)`, project, r.PathValue("workspace"), board, transactionID, account, canvasOperationsAction, input.RequestID, payloadDigest(input), status, bodyRaw, beforeRaw, versionsRaw, expires)
+	if err != nil {
+		return err
+	}
+	if err = tx.Commit(); err != nil {
+		return err
+	}
+	if version := versions[board]; version > 0 {
+		setVersion(w, version)
+	}
+	reply(w, status, body)
+	return nil
+}
+
+func (s *service) getCanvasOperation(w http.ResponseWriter, r *http.Request, project, account string) error {
+	if r.Method != http.MethodGet {
+		reject(w, 405, "method_not_allowed")
+		return nil
+	}
+	key := r.PathValue("request")
+	if !uuidSlugPattern.MatchString(key) {
+		reject(w, 400, "invalid_request_id")
+		return nil
+	}
+	tx, err := s.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	workspace, board := r.PathValue("workspace"), r.PathValue("material")
+	if _, _, err = lockMaterial(r.Context(), tx, project, workspace, board, account); err != nil {
+		return err
+	}
+	var raw json.RawMessage
+	err = tx.QueryRowContext(r.Context(), `SELECT response_body FROM canvas_transactions WHERE project=$1 AND workspace_id=$2 AND board_id=$3 AND account_id=$4 AND action=$5 AND idempotency_key=$6`, project, workspace, board, account, canvasOperationsAction, key).Scan(&raw)
+	if err == sql.ErrNoRows {
+		reply(w, 404, response{"status": "unknown", "error": "operation_receipt_unknown", "request_id": key})
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	var result struct {
+		Snapshots []canvasSnapshot `json:"snapshots"`
+	}
+	if err = json.Unmarshal(raw, &result); err != nil {
+		return err
+	}
+	for _, snapshot := range result.Snapshots {
+		if _, _, err = lockMaterial(r.Context(), tx, project, workspace, snapshot.BoardID, account); err != nil {
+			return err
+		}
+	}
+	if err = tx.Rollback(); err != nil {
+		return err
+	}
+	reply(w, 200, raw)
+	return nil
+}

internal/platform/canvas_operations_integration_test.go

@@ -0,0 +1,166 @@
+package platform
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"sync"
+	"testing"
+)
+
+func TestCanvasOperationsTransactions(t *testing.T) {
+	dsn := os.Getenv("PLATFORM_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("requires an isolated integration database")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	ctx := context.Background()
+	var entropy [12]byte
+	_, _ = rand.Read(entropy[:])
+	project := "operations-" + hex.EncodeToString(entropy[:])
+	defer func() {
+		for _, table := range []string{"canvas_transactions", "workspaces", "project_accounts"} {
+			_, _ = db.ExecContext(ctx, "DELETE FROM "+table+" WHERE project=$1", project)
+		}
+	}()
+	accounts, tokens := []string{}, []string{}
+	for range 2 {
+		var account string
+		if err = db.QueryRowContext(ctx, `INSERT INTO project_accounts(project,id) VALUES($1,gen_random_uuid()) RETURNING id::text`, project).Scan(&account); err != nil {
+			t.Fatal(err)
+		}
+		var value [32]byte
+		_, _ = rand.Read(value[:])
+		token := base64.RawURLEncoding.EncodeToString(value[:])
+		hash := sha256.Sum256([]byte(token))
+		if _, err = db.ExecContext(ctx, `INSERT INTO project_sessions(token_hash,project,account_id,expires_at) VALUES($1,$2,$3,now()+interval '1 hour')`, base64.RawURLEncoding.EncodeToString(hash[:]), project, account); err != nil {
+			t.Fatal(err)
+		}
+		accounts, tokens = append(accounts, account), append(tokens, token)
+	}
+	var workspace string
+	if err = db.QueryRowContext(ctx, `INSERT INTO workspaces(project,name,owner_id) VALUES($1,'Operations',$2) RETURNING id::text`, project, accounts[0]).Scan(&workspace); err != nil {
+		t.Fatal(err)
+	}
+	for i, role := range []string{"admin", "viewer"} {
+		if _, err = db.ExecContext(ctx, `INSERT INTO workspace_members(project,workspace_id,account_id,role) VALUES($1,$2,$3,$4)`, project, workspace, accounts[i], role); err != nil {
+			t.Fatal(err)
+		}
+	}
+	boards := []string{}
+	for range 2 {
+		var board string
+		if err = db.QueryRowContext(ctx, `INSERT INTO materials(project,workspace_id,kind,title,created_by,canvas_document) VALUES($1,$2,'board','Board',$3,$4) RETURNING id::text`, project, workspace, accounts[0], json.RawMessage(operationsFixture)).Scan(&board); err != nil {
+			t.Fatal(err)
+		}
+		boards = append(boards, board)
+	}
+	mux := http.NewServeMux()
+	Register(mux, db, map[string]string{project: "https://app.example.com/auth/callback"}, "https://api.example.com", nil)
+	path := "/projects/" + project + "/workspaces/" + workspace + "/materials/" + boards[0] + "/canvas/operations"
+	key := func(n int) string { return fmt.Sprintf("a0000000-0000-4000-8000-%012d", n) }
+	do := func(method, path, token string, input canvasOperationBatch) *httptest.ResponseRecorder {
+		encoded, _ := json.Marshal(input)
+		request := httptest.NewRequest(method, path, bytes.NewReader(encoded))
+		request.Header.Set("Authorization", "Bearer "+token)
+		request.Header.Set("Accept", "application/vnd.foundry.canvas+json;version=2")
+		request.Header.Set("Idempotency-Key", input.RequestID)
+		writer := httptest.NewRecorder()
+		mux.ServeHTTP(writer, request)
+		return writer
+	}
+	call := func(method, path, token string, input canvasOperationBatch, status int) response {
+		t.Helper()
+		writer := do(method, path, token, input)
+		if writer.Code != status {
+			t.Fatalf("%s %s got %d %s want %d", method, path, writer.Code, writer.Body.String(), status)
+		}
+		out := response{}
+		if err := json.Unmarshal(writer.Body.Bytes(), &out); err != nil {
+			t.Fatal(err)
+		}
+		return out
+	}
+	version := func(board string) int64 {
+		t.Helper()
+		var value int64
+		if err := db.QueryRowContext(ctx, `SELECT canvas_version FROM materials WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, board).Scan(&value); err != nil {
+			t.Fatal(err)
+		}
+		return value
+	}
+	batch := func(n int, expected int64) canvasOperationBatch {
+		return canvasOperationBatch{ProtocolVersion: 1, RequestID: key(n), ExpectedVersions: map[string]int64{boards[0]: expected}, Operations: []canvasOperation{{ID: key(n + 100), Type: "node.patch", CanvasID: boards[0], ElementID: "a", Patch: map[string]json.RawMessage{"data": json.RawMessage(`{"title":"renamed"}`)}}}}
+	}
+	firstBody := batch(1, 1)
+	first := call("POST", path, tokens[0], firstBody, 200)
+	retried := call("POST", path, tokens[0], firstBody, 200)
+	if first["transaction_id"] != retried["transaction_id"] || version(boards[0]) != 2 {
+		t.Fatal("retry duplicated writes or changed receipt identity")
+	}
+	queried := call("GET", path+"/"+key(1), tokens[0], canvasOperationBatch{}, 200)
+	if queried["status"] != "applied" || queried["transaction_id"] != first["transaction_id"] {
+		t.Fatal("lost acknowledgment cannot be resolved by request identity")
+	}
+	altered := batch(1, 2)
+	call("POST", path, tokens[0], altered, 409)
+	call("GET", path+"/"+key(1), tokens[1], canvasOperationBatch{}, 404)
+	call("POST", path, tokens[1], batch(2, 2), 403)
+	unknown := call("GET", path+"/"+key(999), tokens[0], canvasOperationBatch{}, 404)
+	if unknown["status"] != "unknown" || unknown["terminal"] == true {
+		t.Fatal("missing receipt must not claim terminal zero writes")
+	}
+	// Terminal zero-write responses must remain queryable and reserve their frozen body.
+	stale := batch(3, 1)
+	rejected := call("POST", path, tokens[0], stale, 412)
+	proof := call("GET", path+"/"+key(3), tokens[0], canvasOperationBatch{}, 200)
+	if proof["status"] != "not-applied" || proof["terminal"] != true || proof["transaction_id"] != rejected["transaction_id"] {
+		t.Fatal("terminal rejection was not persisted")
+	}
+	call("POST", path, tokens[0], batch(3, 2), 409)
+	if version(boards[0]) != 2 {
+		t.Fatal("rejected request performed a write")
+	}
+	// Concurrent exact retries serialize to one transaction and one version increment.
+	concurrent := batch(4, 2)
+	var wait sync.WaitGroup
+	results := make(chan *httptest.ResponseRecorder, 4)
+	for range 4 {
+		wait.Add(1)
+		go func() { defer wait.Done(); results <- do("POST", path, tokens[0], concurrent) }()
+	}
+	wait.Wait()
+	close(results)
+	for result := range results {
+		if result.Code != 200 {
+			t.Fatalf("concurrent retry got %d %s", result.Code, result.Body.String())
+		}
+	}
+	if version(boards[0]) != 3 {
+		t.Fatal("concurrent request executed more than once")
+	}
+	// A valid first participant and an invalid second participant produce no partial write.
+	atomic := batch(5, 3)
+	atomic.ExpectedVersions[boards[1]] = 1
+	atomic.Operations = append(atomic.Operations, canvasOperation{ID: key(500), Type: "node.delete", CanvasID: boards[1], ElementID: "missing"})
+	call("POST", path, tokens[0], atomic, 400)
+	if version(boards[0]) != 3 || version(boards[1]) != 1 {
+		t.Fatal("invalid multi-canvas batch partially committed")
+	}
+	if call("GET", path+"/"+key(5), tokens[0], canvasOperationBatch{}, 200)["status"] != "not-applied" {
+		t.Fatal("invalid batch lost its terminal receipt")
+	}
+}

internal/platform/canvas_operations_test.go

@@ -0,0 +1,63 @@
+package platform
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+const operationsFixture = `{"schema_version":2,"nodes":[{"id":"a","type":"plainText","position":{"x":0,"y":0},"width":240,"height":72,"data":{"kind":"plain-text","title":"original","text":"hello"}}],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}`
+
+func TestCanvasOperationBatchStagesAndMerges(t *testing.T) {
+	initial := map[string]canvasSnapshot{"board": {BoardID: "board", Version: 7, Document: json.RawMessage(operationsFixture)}}
+	operations := []canvasOperation{
+		{ID: "11111111-1111-4111-8111-111111111111", Type: "node.patch", CanvasID: "board", ElementID: "a", Patch: map[string]json.RawMessage{"data": json.RawMessage(`{"title":"renamed"}`)}},
+		{ID: "22222222-2222-4222-8222-222222222222", Type: "node.patch", CanvasID: "board", ElementID: "a", Patch: map[string]json.RawMessage{"position": json.RawMessage(`{"x":90,"y":20}`)}},
+	}
+	result, err := applyCanvasOperations(initial, operations)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result["board"].Version != 8 {
+		t.Fatal("version did not advance once")
+	}
+	var document struct {
+		Nodes []struct {
+			Position struct{ X float64 }
+			Data     struct {
+				Title string
+				Text  string
+			}
+		}
+	}
+	if err = json.Unmarshal(result["board"].Document, &document); err != nil {
+		t.Fatal(err)
+	}
+	if document.Nodes[0].Data.Title != "renamed" || document.Nodes[0].Data.Text != "hello" || document.Nodes[0].Position.X != 90 {
+		t.Fatal("field merge lost unrelated content")
+	}
+	if string(initial["board"].Document) != operationsFixture {
+		t.Fatal("input snapshot mutated")
+	}
+}
+func TestCanvasOperationBatchRejectsWithoutPartialOutput(t *testing.T) {
+	initial := map[string]canvasSnapshot{"board": {BoardID: "board", Version: 1, Document: json.RawMessage(operationsFixture)}}
+	for _, operation := range []canvasOperation{
+		{ID: "11111111-1111-4111-8111-111111111111", Type: "node.patch", CanvasID: "board", ElementID: "a", Patch: map[string]json.RawMessage{"id": json.RawMessage(`"stolen"`)}},
+		{ID: "11111111-1111-4111-8111-111111111111", Type: "node.patch", CanvasID: "board", ElementID: "missing", Patch: map[string]json.RawMessage{"data": json.RawMessage(`{"title":"no"}`)}},
+		{ID: "11111111-1111-4111-8111-111111111111", Type: "edge.create", CanvasID: "board", ElementID: "edge", Record: json.RawMessage(`{"id":"edge","source":"a","target":"missing"}`)},
+	} {
+		if result, err := applyCanvasOperations(initial, []canvasOperation{operation}); err == nil || result != nil {
+			t.Fatal("invalid batch partially accepted")
+		}
+	}
+}
+func TestCanvasOperationBatchValidatesFinalGraphInsteadOfIntermediateState(t *testing.T) {
+	initial := map[string]canvasSnapshot{"board": {BoardID: "board", Version: 1, Document: json.RawMessage(operationsFixture)}}
+	operations := []canvasOperation{
+		{ID: "11111111-1111-4111-8111-111111111111", Type: "edge.create", CanvasID: "board", ElementID: "edge", Record: json.RawMessage(`{"id":"edge","source":"a","target":"b"}`)},
+		{ID: "22222222-2222-4222-8222-222222222222", Type: "node.create", CanvasID: "board", ElementID: "b", Record: json.RawMessage(`{"id":"b","type":"plainText","position":{"x":20,"y":20},"width":240,"height":72,"data":{"kind":"plain-text","title":"b","text":""}}`)},
+	}
+	if _, err := applyCanvasOperations(initial, operations); err != nil {
+		t.Fatal(err)
+	}
+}

internal/platform/http.go

@@ -76,7 +76,7 @@ func (s *service) protected(callbacks map[string]string, handle endpoint) http.H
 		}
 		if r.Method == http.MethodOptions {
 			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PATCH, DELETE, OPTIONS")
-			w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type, If-Match, Idempotency-Key")
+			w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type, If-Match, Idempotency-Key, X-Expected-Account, X-Resource-Id")
 			reply(w, 204, nil)
 			return
 		}
@@ -88,6 +88,10 @@ func (s *service) protected(callbacks map[string]string, handle endpoint) http.H
 		account := session.AccountID
 		if err == nil {
 			auth.WriteSessionHeaders(w, session)
+			if expected := r.Header.Get("X-Expected-Account"); expected != "" && expected != account {
+				reject(w, 409, "identity_changed")
+				return
+			}
 		}
 		if err == nil && r.PathValue("workspace") != "" {
 			var id string
@@ -103,12 +107,21 @@ func (s *service) protected(callbacks map[string]string, handle endpoint) http.H
 				r.SetPathValue("material", id)
 			}
 		}
+		if err == nil {
+			var stopped bool
+			stopped, err = s.guardLegacyCanonicalRequest(w, r, project, account)
+			if stopped {
+				return
+			}
+		}
 		if err == nil {
 			err = handle(w, r, project, account)
 		}
 		if err != nil {
 			var pg *pgconn.PgError
 			switch {
+			case errors.As(err, &pg) && pg.Code == "55000" && pg.Message == "canonical_write_required":
+				reject(w, 409, "canonical_write_required")
 			case errors.Is(err, errSubgraphCycle):
 				reject(w, 409, "subgraph_cycle")
 			case errors.Is(err, errSubgraphDepth):
@@ -137,16 +150,25 @@ func Register(mux *http.ServeMux, db *sql.DB, callbacks map[string]string, origi
 	}
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials", s.protected(callbacks, s.materials))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets", s.protected(callbacks, s.uploadAsset))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/operations/{request}", s.protected(callbacks, s.assetOperation))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/metadata/{asset}", s.protected(callbacks, s.getAssetMetadata))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/assets/{asset}", s.protected(callbacks, s.getAsset))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}", s.protected(callbacks, s.material))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas", s.protected(callbacks, s.canvas))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/models", s.protected(callbacks, s.canvasAIModels))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/operations/{request}", s.protected(callbacks, s.getCanvasAIAdmission))
 	mux.HandleFunc("POST /projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/runs", s.protected(callbacks, s.createCanvasAIRun))
 	mux.HandleFunc("GET /projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/runs", s.protected(callbacks, s.listCanvasAIRuns))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/runs/{run}", s.protected(callbacks, s.getCanvasAIRun))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/runs/{run}/cancel", s.protected(callbacks, s.cancelCanvasAIRun))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/ai/runs/{run}/apply", s.protected(callbacks, s.applyCanvasAIOutput))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/capabilities", s.protected(callbacks, s.canvasCapabilities))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/operations", s.protected(callbacks, s.submitCanvasOperations))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/operations/{request}", s.protected(callbacks, s.getCanvasOperation))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/model", s.protected(callbacks, s.getCanvasModel))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/model/migrate", s.protected(callbacks, s.migrateCanonicalCanvas))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/model/operations", s.protected(callbacks, s.submitCanvasModelOperations))
+	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/model/operations/{request}", s.protected(callbacks, s.getCanvasModelOperation))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/connections", s.protected(callbacks, s.createCanvasConnection))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/subgraphs", s.protected(callbacks, s.createSubgraph))
 	mux.HandleFunc("/projects/{project}/workspaces/{workspace}/materials/{material}/canvas/subgraphs/migrate", s.protected(callbacks, s.migrateSubgraphs))

internal/platform/integration_test.go

@@ -495,7 +495,7 @@ func TestOnboardingAndSharing(t *testing.T) {
 	if err := png.Encode(&assetPNG, image.NewRGBA(image.Rect(0, 0, 3, 2))); err != nil {
 		t.Fatal(err)
 	}
-	upload := func(encoded []byte, key string, status int) response {
+	upload := func(encoded []byte, key string, status int, resourceIDs ...string) response {
 		t.Helper()
 		var body bytes.Buffer
 		writer := multipart.NewWriter(&body)
@@ -509,6 +509,9 @@ func TestOnboardingAndSharing(t *testing.T) {
 		request.Header.Set("Authorization", "Bearer "+tokens[0])
 		request.Header.Set("Content-Type", writer.FormDataContentType())
 		request.Header.Set("Idempotency-Key", key)
+		if len(resourceIDs) > 0 {
+			request.Header.Set("X-Resource-Id", resourceIDs[0])
+		}
 		result := httptest.NewRecorder()
 		mux.ServeHTTP(result, request)
 		if result.Code != status {
@@ -525,6 +528,33 @@ func TestOnboardingAndSharing(t *testing.T) {
 	if uploaded["id"] != retriedAsset["id"] || uploaded["mime_type"] != "image/png" {
 		t.Fatal("asset idempotency or actual MIME detection")
 	}
+	// New uploads keep the resource identity allocated in the frontend durable cut.
+	resourceID, resourceKey := modelTestID(9100), modelTestID(9101)
+	managed := upload(assetPNG.Bytes(), resourceKey, 201, resourceID)
+	if managed["protocol_version"] != float64(2) || managed["request_id"] != resourceKey || managed["asset"].(map[string]any)["id"] != resourceID {
+		t.Fatal("upload did not retain client resource identity")
+	}
+	repeated := upload(assetPNG.Bytes(), resourceKey, 201, resourceID)
+	if !modelEqual(managed, repeated) {
+		t.Fatal("resource retry changed receipt")
+	}
+	lookup := call("GET", workspacePath+"/assets/operations/"+resourceKey, tokens[0], nil, 200)
+	if lookup["status"] != "applied" || !modelEqual(lookup["asset"], managed["asset"]) {
+		t.Fatal("lost upload acknowledgment cannot be recovered")
+	}
+	unknown := call("GET", workspacePath+"/assets/operations/"+modelTestID(9102), tokens[0], nil, 404)
+	if unknown["status"] != "unknown" || unknown["terminal"] == true {
+		t.Fatal("missing asset receipt misreported zero-write")
+	}
+	call("GET", workspacePath+"/assets/operations/"+resourceKey, tokens[2], nil, 404)
+	upload(assetPNG.Bytes(), resourceKey, 409, modelTestID(9103))
+	upload(assetPNG.Bytes(), modelTestID(9104), 409, resourceID)
+	var alternatePNG bytes.Buffer
+	if err := png.Encode(&alternatePNG, image.NewRGBA(image.Rect(0, 0, 4, 4))); err != nil {
+		t.Fatal(err)
+	}
+	upload(alternatePNG.Bytes(), resourceKey, 409, resourceID)
+	upload(assetPNG.Bytes(), modelTestID(9105), 400, "invalid-resource")
 	download := func(token string, status int) {
 		t.Helper()
 		request := httptest.NewRequest("GET", workspacePath+"/assets/"+uploaded["id"].(string), nil)
@@ -554,9 +584,36 @@ func TestOnboardingAndSharing(t *testing.T) {
 			t.Fatal("preview changed small original or privacy headers")
 		}
 	}
+	// Metadata discloses the same immutable identity only after a fresh read permission check.
+	metadataPath := workspacePath + "/assets/metadata/" + uploaded["id"].(string)
+	for _, sample := range []struct {
+		token  string
+		status int
+	}{{tokens[0], 200}, {tokens[1], 404}, {tokens[2], 404}} {
+		request := httptest.NewRequest("GET", metadataPath, nil)
+		request.Header.Set("Authorization", "Bearer "+sample.token)
+		result := httptest.NewRecorder()
+		mux.ServeHTTP(result, request)
+		if result.Code != sample.status {
+			t.Fatalf("metadata permission got %d want %d: %s", result.Code, sample.status, result.Body.String())
+		}
+		if result.Code == 200 {
+			var metadata response
+			if err := json.Unmarshal(result.Body.Bytes(), &metadata); err != nil {
+				t.Fatal(err)
+			}
+			digest := sha256.Sum256(assetPNG.Bytes())
+			if metadata["metadata_version"] != float64(1) || metadata["sha256"] != hex.EncodeToString(digest[:]) || !modelEqual(metadata["asset"], uploaded) {
+				t.Fatalf("invalid metadata identity: %s", result.Body.String())
+			}
+			if result.Header().Get("Cache-Control") != "private, no-store" {
+				t.Fatalf("invalid metadata privacy header: %q", result.Header().Get("Cache-Control"))
+			}
+		}
+	}
 	// Neither a snapshot nor an asset response may keep the workspace locked
 	// while a slow downstream consumer is accepting its body.
-	for _, path := range []string{canvasPath, workspacePath + "/assets/" + uploaded["id"].(string)} {
+	for _, path := range []string{canvasPath, workspacePath + "/assets/" + uploaded["id"].(string), metadataPath} {
 		var probeErr error
 		writer := &readLockProbe{ResponseRecorder: httptest.NewRecorder(), probe: func() {
 			lockTx, e := db.BeginTx(ctx, nil)
@@ -649,6 +706,62 @@ func TestOnboardingAndSharing(t *testing.T) {
 		t.Fatalf("stable URL lost child asset binding: %v count=%d", err, managedBindings)
 	}
 	call("POST", assetCanvasPath+"/subgraphs/asset-frame/dissolve", tokens[0], response{"expected_versions": map[string]int64{assetBoard["id"].(string): 5, assetChild: 2}}, 200, "", accept, "40000000-0000-4000-8000-000000000003")
+	// A warm metadata/original cache is not a future permission grant. An external
+	// collaborator can read through a source board grant, but a new canonical
+	// target write must recheck asset readability after that grant is revoked.
+	sourceGrantPath := workspacePath + "/materials/" + assetBoard["id"].(string) + "/grants"
+	call("POST", sourceGrantPath, tokens[0], response{"account_id": accounts[2], "role": "viewer"}, 204)
+	call("GET", metadataPath, tokens[2], nil, 200)
+	download(tokens[2], 200)
+	targetBoard := call("POST", workspacePath+"/materials", tokens[0], response{"kind": "board", "title": "Asset adoption target", "content": response{}}, 201)
+	targetID := targetBoard["id"].(string)
+	targetPath := workspacePath + "/materials/" + targetID
+	targetGrantPath := targetPath + "/grants"
+	call("POST", targetGrantPath, tokens[0], response{"account_id": accounts[2], "role": "editor"}, 204)
+	migrationID := modelTestID(9200)
+	call("POST", targetPath+"/canvas/model/migrate", tokens[0], response{"protocol_version": 2, "request_id": migrationID, "expected_versions": map[string]int64{targetID: 1}}, 200, "", accept, migrationID)
+	targetModel := call("GET", targetPath+"/canvas/model", tokens[2], nil, 200)["model"].(map[string]any)
+	targetVersion := int64(targetModel["versions"].(map[string]any)[targetID].(float64))
+	adoptedElement := modelTestNode(modelTestID(9201), targetID)
+	adoptedElement["componentId"] = "image"
+	adoptedElement["data"] = map[string]any{"title": "Adopted", "text": "", "assetId": uploaded["id"], "src": uploaded["url"]}
+	adoptionRequest := func(requestID, operationID string) modelBatch {
+		return modelBatch{ProtocolVersion: 2, RequestID: requestID, Expected: map[string]int64{targetID: targetVersion}, Operations: []modelOperation{{ID: operationID, Changes: []modelChange{{Kind: "element", ID: modelString(adoptedElement["id"]), Before: modelJSON(nil), After: modelJSON(adoptedElement)}}}}}
+	}
+	call("DELETE", sourceGrantPath+"/"+accounts[2], tokens[0], nil, 204)
+	call("GET", metadataPath, tokens[2], nil, 404)
+	download(tokens[2], 404)
+	deniedID := modelTestID(9202)
+	deniedBody := adoptionRequest(deniedID, modelTestID(9203))
+	denied := call("POST", targetPath+"/canvas/model/operations", tokens[2], deniedBody, 400, "", accept, deniedID)
+	if denied["status"] != "not-applied" || denied["terminal"] != true || denied["error"] != "invalid_asset_reference" {
+		t.Fatalf("revoked source did not yield a definitive no-write receipt: %v", denied)
+	}
+	unchanged := call("GET", targetPath+"/canvas/model", tokens[2], nil, 200)["model"].(map[string]any)
+	if !modelEqual(unchanged, targetModel) {
+		t.Fatal("revoked-source adoption changed target model or versions")
+	}
+	var targetBindings int
+	if err := db.QueryRowContext(ctx, "SELECT count(*) FROM canvas_asset_bindings WHERE project=$1 AND asset_id=$2 AND board_id=$3", project, uploaded["id"], targetID).Scan(&targetBindings); err != nil || targetBindings != 0 {
+		t.Fatalf("rejected adoption left a target binding: %d %v", targetBindings, err)
+	}
+	// Restoring source access does not change the frozen rejected request's result.
+	call("POST", sourceGrantPath, tokens[0], response{"account_id": accounts[2], "role": "viewer"}, 204)
+	call("GET", metadataPath, tokens[2], nil, 200)
+	replayedDenial := call("POST", targetPath+"/canvas/model/operations", tokens[2], deniedBody, 400, "", accept, deniedID)
+	if !modelEqual(denied, replayedDenial) {
+		t.Fatal("permission restoration changed a terminal receipt")
+	}
+	acceptedID := modelTestID(9204)
+	call("POST", targetPath+"/canvas/model/operations", tokens[2], adoptionRequest(acceptedID, modelTestID(9205)), 200, "", accept, acceptedID)
+	call("DELETE", sourceGrantPath+"/"+accounts[2], tokens[0], nil, 204)
+	// The independently authorized target now owns a binding; source revocation
+	// must not revoke a resource still readable through that target.
+	call("GET", metadataPath, tokens[2], nil, 200)
+	download(tokens[2], 200)
+	call("DELETE", targetGrantPath+"/"+accounts[2], tokens[0], nil, 204)
+	call("GET", metadataPath, tokens[2], nil, 404)
+	download(tokens[2], 404)
 	download(tokens[1], 200)
 	upload([]byte("not an image"), "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa", 400)
 

internal/platform/subgraph_migration_http.go

@@ -44,14 +44,22 @@ func (s *service) saveCanvas(r *http.Request, tx *sql.Tx, project, workspace str
 	if err := tx.QueryRowContext(r.Context(), `SELECT COALESCE(canvas_document,'{"schema_version":1,"nodes":[],"edges":[],"viewport":{"x":0,"y":0,"zoom":1}}'::jsonb) FROM materials WHERE project=$1 AND workspace_id=$2 AND id=$3 FOR UPDATE`, project, workspace, snapshot.BoardID).Scan(&before); err != nil {
 		return err
 	}
-	if err := invalidateCanvasAITargets(r, tx, project, workspace, snapshot.BoardID, before, snapshot.Document); err != nil {
+	root, err := canonicalRoot(r.Context(), tx, project, workspace, snapshot.BoardID)
+	if err != nil {
 		return err
 	}
+	// Canonical lifecycle invalidation runs once against normalized identities.
+	// Its compatibility projection must not mistake an owner move for deletion.
+	if root == "" {
+		if err := invalidateCanvasAITargets(r, tx, project, workspace, snapshot.BoardID, before, snapshot.Document); err != nil {
+			return err
+		}
+	}
 
 	if err := s.attachCanvasAssets(r, tx, project, workspace, snapshot.BoardID, snapshot.Document); err != nil {
 		return err
 	}
-	_, err := tx.ExecContext(r.Context(), `UPDATE materials SET canvas_document=$4,canvas_version=$5 WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, snapshot.BoardID, snapshot.Document, snapshot.Version)
+	_, err = tx.ExecContext(r.Context(), `UPDATE materials SET canvas_document=$4,canvas_version=$5 WHERE project=$1 AND workspace_id=$2 AND id=$3`, project, workspace, snapshot.BoardID, snapshot.Document, snapshot.Version)
 	return err
 }
 

internal/platform/testdata/foundry-model-operation-v2.json

@@ -0,0 +1,26 @@
+{
+  "protocol_version": 2,
+  "request_id": "90000000-0000-4000-8000-000000000002",
+  "expected_versions": {
+    "10000000-0000-4000-8000-000000000001": 3
+  },
+  "operations": [
+    {
+      "id": "90000000-0000-4000-8000-000000000001",
+      "changes": [
+        {
+          "kind": "field",
+          "target": {
+            "id": "a",
+            "incarnation": 1
+          },
+          "field": "data.title",
+          "before": "a",
+          "after": "renamed",
+          "beforePresent": true,
+          "afterPresent": true
+        }
+      ]
+    }
+  ]
+}

internal/research/cursor.go

@@ -0,0 +1,65 @@
+package research
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// Cursors locate a public corpus row, not an account or authentication token.
+// Binding to normalized filters prevents accidentally paging a different query.
+type position struct {
+	Version int    `json:"v"`
+	ID      int64  `json:"id"`
+	Key     string `json:"key"`
+	Before  bool   `json:"before"`
+	Filter  string `json:"filter"`
+}
+
+var errCursor = errors.New("invalid cursor")
+
+func filterKey(f Filters) string {
+	sort, search := f.Sort, f.SearchIn
+	if sort == "" {
+		sort = "recent"
+	}
+	if search == "" {
+		search = "text"
+	}
+	data, _ := json.Marshal([]string{strings.TrimSpace(f.Query), f.Topic, sort, search, strconv.Itoa(f.PageSize)})
+	sum := sha256.Sum256(data)
+	return hex.EncodeToString(sum[:16])
+}
+func encodeCursor(f Filters, p position, before bool) string {
+	p.Version, p.Before, p.Filter = 1, before, filterKey(f)
+	if f.Sort != "title" {
+		p.Key = ""
+	}
+	data, _ := json.Marshal(p)
+	return base64.RawURLEncoding.EncodeToString(data)
+}
+func decodeCursor(f Filters) (position, error) {
+	var p position
+	if f.Cursor == "" {
+		return p, nil
+	}
+	if len(f.Cursor) > 32768 {
+		return p, errCursor
+	}
+	data, err := base64.RawURLEncoding.Strict().DecodeString(f.Cursor)
+	if err != nil {
+		return p, errCursor
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	if decoder.Decode(&p) != nil || decoder.Decode(new(any)) != io.EOF || p.Version != 1 || p.ID <= 0 || p.Filter != filterKey(f) || strings.ContainsRune(p.Key, 0) || (f.Sort != "title" && p.Key != "") {
+		return position{}, errCursor
+	}
+	return p, nil
+}

internal/research/cursor_test.go

@@ -0,0 +1,34 @@
+package research
+
+import (
+	"encoding/base64"
+	"net/url"
+	"strings"
+	"testing"
+)
+
+func TestCursorValidation(t *testing.T) {
+	f := Filters{Query: "graph", Sort: "title", SearchIn: "text", PageSize: 8}
+	f.Cursor = encodeCursor(f, position{ID: 9223372036854775807, Key: "duplicate\x01title"}, true)
+	p, err := decodeCursor(f)
+	if err != nil || !p.Before || p.ID != 9223372036854775807 || p.Key != "duplicate\x01title" {
+		t.Fatalf("roundtrip %+v %v", p, err)
+	}
+	if _, err := parseFilters("q=graph&sort=title&cursor=" + url.QueryEscape(f.Cursor)); err != nil {
+		t.Fatal(err)
+	}
+	for _, raw := range []string{"!", strings.Repeat("a", 32769), base64.RawURLEncoding.EncodeToString([]byte(`{"v":2}`)), f.Cursor + "="} {
+		bad := f
+		bad.Cursor = raw
+		if _, err := decodeCursor(bad); err == nil {
+			t.Fatal("accepted invalid cursor")
+		}
+	}
+	for _, change := range []func(*Filters){func(f *Filters) { f.Query = "other" }, func(f *Filters) { f.Sort = "recent" }, func(f *Filters) { f.PageSize = 9 }, func(f *Filters) { f.SearchIn = "author" }, func(f *Filters) { f.Topic = "cs.AI" }} {
+		bad := f
+		change(&bad)
+		if _, err := decodeCursor(bad); err == nil {
+			t.Fatal("accepted mismatched filter")
+		}
+	}
+}

internal/research/http.go

@@ -49,20 +49,20 @@ type Filters struct {
 	SearchIn string
 	Topic    string
 	Sort     string
-	Page     int
+	Cursor   string
 	PageSize int
 }
 
 type Page struct {
-	Items    []Paper  `json:"items"`
-	Total    int64    `json:"total"`
-	Topics   []string `json:"topics"`
-	Page     int      `json:"page"`
-	PageSize int      `json:"pageSize"`
+	Items          []Paper  `json:"items"`
+	NextCursor     string   `json:"nextCursor"`
+	PreviousCursor string   `json:"previousCursor"`
+	Topics         []string `json:"topics"`
+	PageSize       int      `json:"pageSize"`
 }
 
 // Repository implementations must use a read-only transaction for each List,
-// so its count, topics and page describe the same database snapshot.
+// so its metadata and page describe the same database snapshot.
 type Repository interface {
 	List(context.Context, Filters) (Page, error)
 	Get(context.Context, int64) (Paper, error)
@@ -102,7 +102,7 @@ var topicPattern = regexp.MustCompile(`^[A-Za-z][A-Za-z0-9.-]{0,79}$`)
 var positiveInteger = regexp.MustCompile(`^[1-9][0-9]*$`)
 
 func parseFilters(raw string) (Filters, error) {
-	f := Filters{SearchIn: "text", Sort: "recent", Page: 1, PageSize: 8}
+	f := Filters{SearchIn: "text", Sort: "recent", PageSize: 8}
 	values, err := url.ParseQuery(raw)
 	if err != nil {
 		return f, err
@@ -133,28 +133,23 @@ func parseFilters(raw string) (Filters, error) {
 				return f, invalid
 			}
 			f.Sort = value[0]
-		case "page", "pageSize":
+		case "cursor":
+			f.Cursor = value[0]
+		case "pageSize":
 			if !positiveInteger.MatchString(value[0]) {
 				return f, invalid
 			}
 			n, err := strconv.Atoi(value[0])
-			limit := 1000
-			if key == "pageSize" {
-				limit = 50
-			}
-			if err != nil || n > limit {
+			if err != nil || n > 50 {
 				return f, invalid
 			}
-			if key == "page" {
-				f.Page = n
-			} else {
-				f.PageSize = n
-			}
+			f.PageSize = n
 		default:
 			return f, invalid
 		}
 	}
-	return f, nil
+	_, err = decodeCursor(f)
+	return f, err
 }
 
 func (s *service) serve(w http.ResponseWriter, r *http.Request) {

internal/research/http_test.go

@@ -28,7 +28,7 @@ func (f *fixtureRepository) List(ctx context.Context, filters Filters) (Page, er
 		<-ctx.Done()
 		return Page{}, ctx.Err()
 	}
-	return Page{Items: []Paper{}, Topics: []string{}, Page: filters.Page, PageSize: filters.PageSize}, f.err
+	return Page{Items: []Paper{}, Topics: []string{}, PageSize: filters.PageSize}, f.err
 }
 
 func (f *fixtureRepository) Get(ctx context.Context, id int64) (Paper, error) {
@@ -47,8 +47,8 @@ func TestAnonymousReadRoutes(t *testing.T) {
 	f := &fixtureRepository{}
 	mux := http.NewServeMux()
 	Register(mux, f, map[string]string{"thesisly": "http://localhost:17322/auth/callback"})
-	w := request(mux, "GET", "/projects/thesisly/research/papers?q=graph&searchIn=author&sort=title&topic=cs.LG&page=2&pageSize=10")
-	if w.Code != 200 || f.filters != (Filters{Query: "graph", SearchIn: "author", Topic: "cs.LG", Sort: "title", Page: 2, PageSize: 10}) {
+	w := request(mux, "GET", "/projects/thesisly/research/papers?q=graph&searchIn=author&sort=title&topic=cs.LG&pageSize=10")
+	if w.Code != 200 || f.filters != (Filters{Query: "graph", SearchIn: "author", Topic: "cs.LG", Sort: "title", PageSize: 10}) {
 		t.Fatalf("list: %d %+v", w.Code, f.filters)
 	}
 	var page Page
@@ -95,7 +95,7 @@ func TestInvalidQueriesNeverReachRepository(t *testing.T) {
 
 func TestQueryDefaultsAndUnicode(t *testing.T) {
 	f, err := parseFilters("q=" + url.QueryEscape(" 论文 Graph "))
-	if err != nil || f.Query != "论文 Graph" || f.Page != 1 || f.PageSize != 8 || f.SearchIn != "text" || f.Sort != "recent" {
+	if err != nil || f.Query != "论文 Graph" || f.PageSize != 8 || f.SearchIn != "text" || f.Sort != "recent" {
 		t.Fatalf("%+v %v", f, err)
 	}
 }
@@ -143,3 +143,17 @@ func TestConcurrencyAndTimeoutReleaseSlots(t *testing.T) {
 		t.Fatalf("timeout %d, slots %d", w.Code, len(s.slots))
 	}
 }
+
+func TestInvalidCursorsNeverReachRepository(t *testing.T) {
+	f := Filters{Query: "graph", Sort: "recent", SearchIn: "text", PageSize: 8}
+	valid := encodeCursor(f, position{ID: 42}, false)
+	for _, query := range []string{"cursor=!", "cursor=" + strings.Repeat("a", 32769), "q=different&cursor=" + valid, "cursor=" + valid + "&cursor=" + valid, "page=1"} {
+		repository := &fixtureRepository{}
+		mux := http.NewServeMux()
+		Register(mux, repository, map[string]string{"thesisly": "unused"})
+		w := request(mux, "GET", "/projects/thesisly/research/papers?"+query)
+		if w.Code != 400 || repository.calls != 0 {
+			t.Fatalf("invalid cursor reached storage: status=%d calls=%d", w.Code, repository.calls)
+		}
+	}
+}

internal/research/postgres.go

@@ -173,8 +173,31 @@ func decodeAuthors(raw string) ([]string, error) {
 	return names, nil
 }
 
+func (r *PostgresRepository) positions(ctx context.Context, tx *sql.Tx, query string, args []any) ([]position, error) {
+	rows, err := tx.QueryContext(ctx, r.query(query), args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	positions := []position{}
+	for rows.Next() {
+		var p position
+		// Preserve the stored title key, including the published text codec.
+		if err = rows.Scan(&p.ID, &p.Key); err != nil {
+			return nil, err
+		}
+		positions = append(positions, p)
+	}
+	return positions, rows.Err()
+}
+
 func (r *PostgresRepository) List(ctx context.Context, filters Filters) (Page, error) {
-	result := Page{Items: []Paper{}, Topics: []string{}, Page: filters.Page, PageSize: filters.PageSize}
+	result := Page{Items: []Paper{}, Topics: []string{}, PageSize: filters.PageSize}
+	cursor, err := decodeCursor(filters)
+	if err != nil {
+		return result, err
+	}
+	original := filters
 	tx, err := r.begin(ctx)
 	if err != nil {
 		return result, err
@@ -185,56 +208,168 @@ func (r *PostgresRepository) List(ctx context.Context, filters Filters) (Page, e
 		filters.Topic = encodeText(filters.Topic)
 	}
 	where, args := whereClause(filters)
-	if err = tx.QueryRowContext(ctx, r.query(`SELECT count(*) FROM {schema}papers p`+where), args...).Scan(&result.Total); err != nil {
-		return result, err
+	if cursor.ID != 0 {
+		clause := " AND "
+		if where == "" {
+			clause = " WHERE "
+		}
+		op := "<"
+		if cursor.Before {
+			op = ">"
+		}
+		args = append(args, cursor.ID)
+		if filters.Sort == "title" {
+			if cursor.Before {
+				op = "<"
+			} else {
+				op = ">"
+			}
+			args = append(args, cursor.Key)
+			where += fmt.Sprintf("%s(p.title_key,p.id) %s ($%d::text COLLATE \"C\",$%d)", clause, op, len(args), len(args)-1)
+		} else {
+			where += fmt.Sprintf("%sp.id %s $%d", clause, op, len(args))
+		}
 	}
 	order := "p.id DESC"
 	if filters.Sort == "title" {
 		order = "p.title_key,p.id"
 	}
-	args = append(args, filters.PageSize, (filters.Page-1)*filters.PageSize)
-	// Select IDs before loading potentially TOASTed titles/abstracts. With
-	// sparse categories, selecting full rows here can make the planner walk
-	// hundreds of thousands of wide heap rows before finding eight matches.
-	candidateQuery := `SELECT p.id FROM {schema}papers p`
-	candidateOrder := order
-	prefix := ""
-	if where != "" {
-		columns := "p.id"
+	if cursor.Before {
+		order = "p.id"
 		if filters.Sort == "title" {
-			columns += ",p.title_key"
+			order = "p.title_key DESC,p.id DESC"
 		}
-		// Apply search before LIMIT/ORDER BY so a sparse term cannot turn
-		// into a backward heap scan that recomputes vectors for millions.
-		prefix = fmt.Sprintf(`matches AS MATERIALIZED (SELECT %s FROM {schema}papers p%s), `, columns, where)
-		candidateQuery = "SELECT id FROM matches"
-		candidateOrder = strings.ReplaceAll(order, "p.", "")
 	}
-	query := fmt.Sprintf(`WITH %spage_ids AS MATERIALIZED (
-		%s ORDER BY %s LIMIT $%d OFFSET $%d
-		) SELECT p.id,p.title,p.abstract,p.authors_json,p.first_published
-		FROM page_ids JOIN {schema}papers p ON p.id=page_ids.id ORDER BY %s`, prefix, candidateQuery, candidateOrder, len(args)-1, len(args), order)
-	rows, err := tx.QueryContext(ctx, r.query(query), args...)
-	if err != nil {
-		return result, err
+	args = append(args, filters.PageSize+1)
+	columns := "p.id,p.title_key"
+	if filters.Sort != "title" {
+		columns = "p.id, ''::text AS title_key"
 	}
-	for rows.Next() {
-		p, err := r.scanPaper(rows)
+	// Search candidates are materialized to avoid scanning millions of wide
+	// rows in ID order for sparse terms. There is no count or deep OFFSET.
+	query := fmt.Sprintf("SELECT %s FROM {schema}papers p%s ORDER BY %s LIMIT $%d", columns, where, order, len(args))
+	if filters.Query != "" || filters.Topic != "" {
+		query = fmt.Sprintf("WITH matches AS MATERIALIZED (SELECT %s FROM {schema}papers p%s) SELECT p.id,p.title_key FROM matches p ORDER BY %s LIMIT $%d", columns, where, order, len(args))
+	}
+	positions := []position{}
+	topicOnly := filters.Sort != "title" && filters.Topic != "" && filters.Query == ""
+	if topicOnly {
+		// The published paper_tags foreign key guarantees these IDs exist.
+		// Walk the (tag_id,paper_id) index instead of joining all matching
+		// paper rows before LIMIT. DISTINCT removes duplicate source evidence.
+		topicArgs := []any{filters.Topic, filters.PageSize + 1}
+		predicate := ""
+		if cursor.ID != 0 {
+			op := "<"
+			if cursor.Before {
+				op = ">"
+			}
+			topicArgs = append(topicArgs, cursor.ID)
+			predicate = " AND pt.paper_id " + op + " $3"
+		}
+		direction := "DESC"
+		if cursor.Before {
+			direction = "ASC"
+		}
+		query := fmt.Sprintf(`SELECT DISTINCT pt.paper_id,''::text AS title_key FROM {schema}paper_tags pt
+		 WHERE pt.tag_id=(SELECT id FROM {schema}tags WHERE namespace='arxiv:category' AND value=$1)%s
+		 ORDER BY pt.paper_id %s LIMIT $2`, predicate, direction)
+		positions, err = r.positions(ctx, tx, query, topicArgs)
 		if err != nil {
-			_ = rows.Close()
 			return result, err
 		}
-		result.Items = append(result.Items, p)
 	}
-	err = rows.Err()
-	_ = rows.Close()
-	if err != nil {
-		return result, err
+	if !topicOnly && filters.Sort != "title" && (filters.Query != "" || filters.Topic != "") {
+		// Common terms can fill a page near its cursor. Probe a bounded ID
+		// interval first; never scan the entire heap in order for a rare term.
+		// If the interval has fewer than size+1 matches, discard it and use
+		// the complete indexed search below. No matches are silently omitted.
+		anchor := cursor.ID
+		if anchor == 0 {
+			if err = tx.QueryRowContext(ctx, r.query(`SELECT coalesce(max(id),0) FROM {schema}papers`)).Scan(&anchor); err != nil {
+				return result, err
+			}
+		}
+		for _, window := range []int64{512, 4096} {
+			bound, op := int64(0), ">="
+			if anchor > window {
+				bound = anchor - window
+			}
+			if cursor.Before {
+				bound, op = int64(9223372036854775807), "<="
+				if anchor <= 9223372036854775807-window {
+					bound = anchor + window
+				}
+			}
+			boundedArgs := append(append([]any{}, args...), bound)
+			bounded := fmt.Sprintf("SELECT %s FROM {schema}papers p%s AND p.id %s $%d ORDER BY %s LIMIT $%d", columns, where, op, len(boundedArgs), order, len(args))
+			positions, err = r.positions(ctx, tx, bounded, boundedArgs)
+			if err != nil {
+				return result, err
+			}
+			// Expand once only when there is evidence of nearby matches.
+			// Zero matches goes straight to the sparse-term index fallback.
+			if len(positions) == 0 || len(positions) >= filters.PageSize+1 {
+				break
+			}
+		}
+	}
+	if !topicOnly && len(positions) < filters.PageSize+1 {
+		positions, err = r.positions(ctx, tx, query, args)
+		if err != nil {
+			return result, err
+		}
+	}
+	more := len(positions) > filters.PageSize
+	if more {
+		positions = positions[:filters.PageSize]
+	}
+	if cursor.Before {
+		for i, j := 0, len(positions)-1; i < j; i, j = i+1, j-1 {
+			positions[i], positions[j] = positions[j], positions[i]
+		}
+	}
+	if len(positions) > 0 {
+		if (!cursor.Before && cursor.ID != 0) || (cursor.Before && more) {
+			result.PreviousCursor = encodeCursor(original, positions[0], true)
+		}
+		if (!cursor.Before && more) || (cursor.Before && cursor.ID != 0) {
+			result.NextCursor = encodeCursor(original, positions[len(positions)-1], false)
+		}
+		ids := make([]int64, len(positions))
+		byID := map[string]Paper{}
+		for i, p := range positions {
+			ids[i] = p.ID
+		}
+		rows, err := tx.QueryContext(ctx, r.query(`SELECT id,title,abstract,authors_json,first_published FROM {schema}papers WHERE id=ANY($1)`), ids)
+		if err != nil {
+			return result, err
+		}
+		for rows.Next() {
+			p, scanErr := r.scanPaper(rows)
+			if scanErr != nil {
+				_ = rows.Close()
+				return result, scanErr
+			}
+			byID[p.ID] = p
+		}
+		err = rows.Err()
+		_ = rows.Close()
+		if err != nil {
+			return result, err
+		}
+		for _, p := range positions {
+			paper, exists := byID[strconv.FormatInt(p.ID, 10)]
+			if !exists {
+				return result, errors.New("inconsistent paper index")
+			}
+			result.Items = append(result.Items, paper)
+		}
 	}
 	if err = r.enrich(ctx, tx, result.Items); err != nil {
 		return result, err
 	}
-	rows, err = tx.QueryContext(ctx, r.query(`SELECT value FROM {schema}tags WHERE namespace='arxiv:category' ORDER BY value`))
+	rows, err := tx.QueryContext(ctx, r.query(`SELECT value FROM {schema}tags WHERE namespace='arxiv:category' ORDER BY value`))
 	if err != nil {
 		return result, err
 	}
@@ -271,7 +406,7 @@ func (r *PostgresRepository) Get(ctx context.Context, id int64) (Paper, error) {
 	return papers[0], tx.Commit()
 }
 
-// Batch metadata queries avoid per-paper round trips and share the count/page
+// Batch metadata queries avoid per-paper round trips and share the page
 // snapshot. User values are bound; only the validated schema is interpolated.
 func (r *PostgresRepository) enrich(ctx context.Context, tx *sql.Tx, papers []Paper) error {
 	if len(papers) == 0 {

internal/research/postgres_integration_test.go

@@ -50,31 +50,28 @@ func TestPostgresPageSearchAndFilters(t *testing.T) {
 	}
 	for _, test := range []struct {
 		filters Filters
-		total   int64
 		ids     []string
 	}{
-		{Filters{Page: 1, PageSize: 2}, 5, []string{"5", "4"}},
-		{Filters{Page: 2, PageSize: 2}, 5, []string{"3", "2"}},
-		{Filters{Page: 3, PageSize: 2}, 5, []string{"1"}},
-		{Filters{Page: 1, PageSize: 2, Sort: "title"}, 5, []string{"2", "5"}},
-		{Filters{Page: 1, PageSize: 8, Query: "graph"}, 2, []string{"3", "1"}},
-		{Filters{Page: 1, PageSize: 8, Query: "graph OR zebra"}, 0, []string{}},
-		{Filters{Page: 1, PageSize: 8, Query: "Ada Smith", SearchIn: "author"}, 1, []string{"1"}},
-		{Filters{Page: 1, PageSize: 8, Topic: "cs.LG"}, 1, []string{"1"}},
-		{Filters{Page: 1, PageSize: 8, Topic: "cs.DC", Query: "graph"}, 1, []string{"3"}},
-		{Filters{Page: 1, PageSize: 8, Query: `x'); DROP TABLE papers;--`}, 0, []string{}},
+		{Filters{PageSize: 2}, []string{"5", "4"}},
+		{Filters{PageSize: 2, Sort: "title"}, []string{"2", "5"}},
+		{Filters{PageSize: 8, Query: "graph"}, []string{"3", "1"}},
+		{Filters{PageSize: 8, Query: "graph OR zebra"}, []string{}},
+		{Filters{PageSize: 8, Query: "Ada Smith", SearchIn: "author"}, []string{"1"}},
+		{Filters{PageSize: 8, Topic: "cs.LG"}, []string{"1"}},
+		{Filters{PageSize: 8, Topic: "cs.DC", Query: "graph"}, []string{"3"}},
+		{Filters{PageSize: 8, Query: `x'); DROP TABLE papers;--`}, []string{}},
 	} {
 		page, err := r.List(ctx, test.filters)
 		if err != nil {
 			t.Fatalf("%+v: %v", test.filters, err)
 		}
-		if page.Total != test.total || !reflect.DeepEqual(paperIDs(page.Items), test.ids) {
-			t.Fatalf("%+v: total=%d ids=%v", test.filters, page.Total, paperIDs(page.Items))
+		if !reflect.DeepEqual(paperIDs(page.Items), test.ids) {
+			t.Fatalf("%+v: ids=%v", test.filters, paperIDs(page.Items))
 		}
 		if !reflect.DeepEqual(page.Topics, []string{"cs.AI", "cs.DC", "cs.LG"}) {
 			t.Fatalf("mixed tag namespaces: %v", page.Topics)
 		}
-		if page.Page != test.filters.Page || page.PageSize != test.filters.PageSize {
+		if page.PageSize != test.filters.PageSize {
 			t.Fatal("lost paging metadata")
 		}
 	}
@@ -143,7 +140,7 @@ func TestPostgresCorpusIsReadOnlyAndHTTPWorks(t *testing.T) {
 	Register(mux, r, map[string]string{"thesisly": "http://localhost:17322/auth/callback"})
 	w := request(mux, "GET", "/projects/thesisly/research/papers?q=graph")
 	var page Page
-	if w.Code != 200 || json.Unmarshal(w.Body.Bytes(), &page) != nil || page.Total != 2 {
+	if w.Code != 200 || json.Unmarshal(w.Body.Bytes(), &page) != nil || len(page.Items) != 2 {
 		t.Fatalf("SQL-backed HTTP list: %d %s", w.Code, w.Body.String())
 	}
 	w = request(mux, "GET", "/projects/thesisly/research/papers/1")
@@ -179,8 +176,174 @@ func TestPostgresPublishedTextCodec(t *testing.T) {
 	if w.Code != 200 || json.Unmarshal(w.Body.Bytes(), &decoded) != nil || decoded.Title != p.Title || decoded.Abstract == nil || *decoded.Abstract != *p.Abstract {
 		t.Fatalf("HTTP lost original control characters: %d %s", w.Code, w.Body.String())
 	}
-	page, err := r.List(ctx, Filters{Page: 1, PageSize: 8, Query: "graph"})
-	if err != nil || page.Total != 2 || len(page.Items) != 2 || page.Items[1].Title != p.Title {
+	page, err := r.List(ctx, Filters{PageSize: 8, Query: "graph"})
+	if err != nil || len(page.Items) != 2 || len(page.Items) != 2 || page.Items[1].Title != p.Title {
 		t.Fatalf("encoded corpus search: %+v %v", page, err)
 	}
 }
+
+func TestPostgresCursorsTraverseBothDirections(t *testing.T) {
+	r, ctx := integrationRepository(t)
+	for _, sort := range []string{"recent", "title"} {
+		f := Filters{Sort: sort, PageSize: 1}
+		seen := []string{}
+		cursors := []string{""}
+		for {
+			page, err := r.List(ctx, f)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(page.Items) != 1 {
+				t.Fatalf("unexpected page %+v", page)
+			}
+			seen = append(seen, page.Items[0].ID)
+			if len(seen) > 5 {
+				t.Fatal("cursor cycle")
+			}
+			if len(seen) > 1 {
+				back := f
+				back.Cursor = page.PreviousCursor
+				prior, err := r.List(ctx, back)
+				if err != nil || len(prior.Items) != 1 || prior.Items[0].ID != seen[len(seen)-2] {
+					t.Fatalf("reverse cursor: %+v %v", prior, err)
+				}
+			} else if page.PreviousCursor != "" {
+				t.Fatal("first page has previous")
+			}
+			if page.NextCursor == "" {
+				break
+			}
+			f.Cursor = page.NextCursor
+			cursors = append(cursors, f.Cursor)
+		}
+		want := []string{"5", "4", "3", "2", "1"}
+		if sort == "title" {
+			want = []string{"2", "5", "1", "3", "4"}
+		}
+		if !reflect.DeepEqual(seen, want) {
+			t.Fatalf("%s: %v", sort, seen)
+		}
+		f.Cursor = cursors[1]
+		f.Query = "different"
+		if _, err := r.List(ctx, f); err == nil {
+			t.Fatal("cursor reused across filters")
+		}
+	}
+}
+
+func TestPostgresEncodedTitleCursors(t *testing.T) {
+	legacy, ctx := integrationRepository(t)
+	r, err := NewPostgresRepository(legacy.db, "research_encoded_fixture")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = r.Check(ctx); err != nil {
+		t.Fatal(err)
+	}
+	f := Filters{Sort: "title", PageSize: 1}
+	seen := []string{}
+	for {
+		page, err := r.List(ctx, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(page.Items) != 1 {
+			t.Fatalf("invalid encoded title page %+v", page)
+		}
+		seen = append(seen, page.Items[0].ID)
+		if len(seen) > 5 {
+			t.Fatal("cursor cycle")
+		}
+		if page.NextCursor == "" {
+			break
+		}
+		f.Cursor = page.NextCursor
+	}
+	if !reflect.DeepEqual(seen, []string{"2", "5", "1", "3", "4"}) {
+		t.Fatalf("encoded key paging %v", seen)
+	}
+}
+
+func TestPostgresBoundedProbeDoesNotTruncateSparseMatches(t *testing.T) {
+	legacy, ctx := integrationRepository(t)
+	r, err := NewPostgresRepository(legacy.db, "research_sparse_fixture")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = r.Check(ctx); err != nil {
+		t.Fatal(err)
+	}
+	for _, size := range []int{1, 2, 3} {
+		f := Filters{Query: "graph", PageSize: size}
+		seen := []string{}
+		var previous []string
+		for {
+			page, err := r.List(ctx, f)
+			if err != nil {
+				t.Fatal(err)
+			}
+			ids := paperIDs(page.Items)
+			if len(ids) == 0 || len(ids) > size {
+				t.Fatalf("invalid sparse page %+v", page)
+			}
+			if previous != nil {
+				back := f
+				back.Cursor = page.PreviousCursor
+				prior, err := r.List(ctx, back)
+				if err != nil || !reflect.DeepEqual(paperIDs(prior.Items), previous) {
+					t.Fatalf("reverse gap %+v %v", prior, err)
+				}
+			}
+			seen = append(seen, ids...)
+			if len(seen) > 5 {
+				t.Fatal("cursor cycle")
+			}
+			previous = ids
+			if page.NextCursor == "" {
+				break
+			}
+			f.Cursor = page.NextCursor
+		}
+		if !reflect.DeepEqual(seen, []string{"10001", "10000", "8000", "3", "1"}) {
+			t.Fatalf("size=%d lost sparse matches %v", size, seen)
+		}
+	}
+}
+
+func TestPostgresTopicCursorSkipsDuplicateEvidence(t *testing.T) {
+	legacy, ctx := integrationRepository(t)
+	r, err := NewPostgresRepository(legacy.db, "research_sparse_fixture")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f := Filters{Topic: "cs.LG", PageSize: 1}
+	seen := []string{}
+	for {
+		page, err := r.List(ctx, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(page.Items) != 1 {
+			t.Fatalf("invalid topic page %+v", page)
+		}
+		seen = append(seen, page.Items[0].ID)
+		if len(seen) > 3 {
+			t.Fatal("cursor cycle")
+		}
+		if len(seen) > 1 {
+			back := f
+			back.Cursor = page.PreviousCursor
+			prior, err := r.List(ctx, back)
+			if err != nil || len(prior.Items) != 1 || prior.Items[0].ID != seen[len(seen)-2] {
+				t.Fatalf("reverse topic %+v %v", prior, err)
+			}
+		}
+		if page.NextCursor == "" {
+			break
+		}
+		f.Cursor = page.NextCursor
+	}
+	if !reflect.DeepEqual(seen, []string{"10001", "10000", "1"}) {
+		t.Fatalf("duplicate evidence or lost topic matches %v", seen)
+	}
+}

internal/research/testdata/corpus.sql

@@ -70,7 +70,8 @@ BEGIN
  END LOOP;
 END $$;
 UPDATE research_encoded_fixture.papers
-SET title='Graph'||chr(1)||chr(1)||'original'||chr(1)||chr(2),
+SET title_key='graph'||chr(1)||chr(1)||'key'||chr(1)||chr(2),
+    title='Graph'||chr(1)||chr(1)||'original'||chr(1)||chr(2),
     abstract='Text'||chr(1)||chr(1)||'tail',
     authors_json='["Ada\u0000Smith","Group\u0001Name"]'
 WHERE id=1;
@@ -79,3 +80,22 @@ SET metadata_json='{"comments":"Original\u0000comment"}' WHERE id=101;
 REVOKE ALL ON SCHEMA research_encoded_fixture FROM PUBLIC;
 GRANT USAGE ON SCHEMA research_encoded_fixture TO foundry_research_fixture;
 GRANT SELECT ON ALL TABLES IN SCHEMA research_encoded_fixture TO foundry_research_fixture;
+
+-- A large ID gap proves the bounded probe cannot truncate sparse results.
+CREATE SCHEMA research_sparse_fixture;
+DO $$
+DECLARE item text;
+BEGIN
+ FOREACH item IN ARRAY ARRAY['papers','sources','source_records','identifiers','tags','paper_tags','venues','editions','submissions','decisions'] LOOP
+  EXECUTE format('CREATE TABLE research_sparse_fixture.%I (LIKE research_fixture.%I INCLUDING ALL)',item,item);
+  EXECUTE format('INSERT INTO research_sparse_fixture.%I SELECT * FROM research_fixture.%I',item,item);
+ END LOOP;
+END $$;
+INSERT INTO research_sparse_fixture.papers VALUES
+ (8000,'Graph in expanded interval','Graph evidence.','graph expanded','[]',NULL),
+ (10000,'Graph near cursor','Graph evidence.','graph near cursor','[]',NULL),
+ (10001,'Graph first','Graph evidence.','graph first','[]',NULL);
+INSERT INTO research_sparse_fixture.paper_tags VALUES(10000,1,'first'),(10000,1,'second'),(10001,1,'first');
+REVOKE ALL ON SCHEMA research_sparse_fixture FROM PUBLIC;
+GRANT USAGE ON SCHEMA research_sparse_fixture TO foundry_research_fixture;
+GRANT SELECT ON ALL TABLES IN SCHEMA research_sparse_fixture TO foundry_research_fixture;