diff --git a/db/010-canvas-ai-receipts.sql b/db/010-canvas-ai-receipts.sql
new file mode 100644
index 0000000..f996970
--- /dev/null
+++ b/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;
diff --git a/internal/platform/canvas_ai_cancel.go b/internal/platform/canvas_ai_cancel.go
index f2b85ac..0aa408c 100644
--- a/internal/platform/canvas_ai_cancel.go
+++ b/internal/platform/canvas_ai_cancel.go
@@ -22,12 +22,41 @@ 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 {
@@ -38,13 +67,25 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	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
 	}
@@ -72,8 +113,7 @@ func (s *service) cancelCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			return err
 		}
 		if role == "viewer" {
-			reject(w, 403, "forbidden")
-			return nil
+			return rejectRequest(403, "forbidden")
 		}
 	}
 	if status == "queued" || status == "running" {
@@ -145,14 +185,14 @@ 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)
 }
diff --git a/internal/platform/canvas_ai_explicit_apply.go b/internal/platform/canvas_ai_explicit_apply.go
index 91347cd..7374ccb 100644
--- a/internal/platform/canvas_ai_explicit_apply.go
+++ b/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
@@ -32,7 +37,15 @@ 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 {
@@ -43,12 +56,24 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 	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 +100,31 @@ 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 canonical && targetBoard != input.TargetCanvasID {
+		return rejectRequest(409, "target_changed")
+	}
 	if node != input.NodeID || status != "conflict" || applied.Valid || runStatus == "cancelled" {
-		reject(w, 409, "output_not_applicable")
-		return nil
+		return rejectRequest(409, "output_not_applicable")
 	}
 	_, role, err = lockMaterial(r.Context(), tx, project, workspace, targetBoard, account)
 	if err != nil {
 		return err
 	}
 	if role == "viewer" {
-		reject(w, 403, "forbidden")
-		return nil
+		return rejectRequest(403, "forbidden")
 	}
 	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(412, "version_conflict")
 	}
 	var output struct {
 		Kind    string `json:"kind"`
@@ -111,40 +139,38 @@ 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")
+	}
 	identityOK, err := canvasAIIdentityMatches(r.Context(), tx, project, workspace, frozen)
 	if err != nil {
 		return err
 	}
 	if !identityOK {
-		reject(w, 409, "target_changed")
-		return nil
+		return rejectRequest(409, "target_changed")
 	}
 	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
@@ -159,17 +185,14 @@ 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")
 	}
 	change, err := prepareCanvasAIPatch(r, tx, project, workspace, snapshot, node, patch)
 	if err != nil {
-		reject(w, 413, "canvas_too_large")
-		return nil
+		return rejectRequest(413, "canvas_too_large")
 	}
 	snapshot = change.Snapshot
 	if err = s.saveCanvasAIChange(r, tx, project, workspace, account, change); err != nil {
@@ -182,6 +205,10 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 	}
 	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.addCanonical(result)
+	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
 	}
@@ -190,10 +217,6 @@ func (s *service) applyCanvasAIOutput(w http.ResponseWriter, r *http.Request, pr
 	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)
 }
diff --git a/internal/platform/canvas_ai_model_integration_test.go b/internal/platform/canvas_ai_model_integration_test.go
index f39d1d0..71fdc0b 100644
--- a/internal/platform/canvas_ai_model_integration_test.go
+++ b/internal/platform/canvas_ai_model_integration_test.go
@@ -272,12 +272,17 @@ func TestCanonicalAIAdmissionAndLifecycle(t *testing.T) {
 	outputID := conflict["outputs"].([]any)[0].(map[string]any)["output"].(map[string]any)["output_id"].(string)
 	applyKey := modelTestID(6200)
 	expected := read().Versions[root]
-	applyInput := response{"node_id": node, "output_id": outputID}
+	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() {
@@ -315,7 +320,16 @@ func TestCanonicalAIAdmissionAndLifecycle(t *testing.T) {
 	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"
-	call("POST", cancelPath, response{}, 200, 0, modelTestID(6202))
+	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")
 	}
@@ -368,7 +382,27 @@ func TestCanonicalAIAdmissionAndLifecycle(t *testing.T) {
 	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.
-	call("POST", base(child)+"/ai/runs", staleInput, 412, read().Versions[child], staleKey)
+	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)
diff --git a/internal/platform/canvas_ai_query.go b/internal/platform/canvas_ai_query.go
index db6ecd7..6ed9c78 100644
--- a/internal/platform/canvas_ai_query.go
+++ b/internal/platform/canvas_ai_query.go
@@ -181,6 +181,14 @@ func (s *service) getCanvasAIAdmission(w http.ResponseWriter, r *http.Request, p
 		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"})
diff --git a/internal/platform/canvas_ai_receipts.go b/internal/platform/canvas_ai_receipts.go
new file mode 100644
index 0000000..5d1c908
--- /dev/null
+++ b/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})
+}
diff --git a/internal/platform/canvas_ai_runs.go b/internal/platform/canvas_ai_runs.go
index ee4634f..7b5ae34 100644
--- a/internal/platform/canvas_ai_runs.go
+++ b/internal/platform/canvas_ai_runs.go
@@ -91,13 +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
@@ -133,8 +141,7 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		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)
@@ -146,12 +153,10 @@ 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")
 	}
 	root, incarnation, _, err := canvasAIIdentity(r.Context(), tx, project, workspace, board, input.NodeID)
 	if err != nil {
@@ -159,21 +164,17 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	}
 	if root != "" {
 		if input.ProtocolVersion != 2 || input.RequestID != key || !uuidSlugPattern.MatchString(input.OperationID) || input.TargetIncarnation < 1 {
-			reject(w, 400, "invalid_ai_protocol")
-			return nil
+			return rejectRequest(400, "invalid_ai_protocol")
 		}
 		if input.TargetIncarnation != incarnation {
-			reject(w, 409, "target_changed")
-			return nil
+			return rejectRequest(409, "target_changed")
 		}
 	} else if input.ProtocolVersion != 0 || input.RequestID != "" || input.TargetIncarnation != 0 || input.OperationID != "" || input.ExpectedVersions != nil {
-		reject(w, 409, "canonical_migration_required")
-		return 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 {
-		reject(w, 400, "invalid_ai_request")
-		return nil
+		return rejectRequest(400, "invalid_ai_request")
 	}
 	if change.Before != nil {
 		if code := validateCanvasAIVersions(*change.Before, board, expected, input.ExpectedVersions); code != "" {
@@ -181,16 +182,14 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			if code == "version_conflict" {
 				status = http.StatusPreconditionFailed
 			}
-			reject(w, status, code)
-			return nil
+			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 {
@@ -200,11 +199,10 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 	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
@@ -222,16 +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") {
@@ -248,12 +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") {
@@ -264,8 +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
 		}
@@ -282,26 +275,22 @@ 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)
@@ -309,8 +298,7 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 			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.
@@ -325,8 +313,7 @@ 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)
@@ -340,6 +327,7 @@ func (s *service) createCanvasAIRun(w http.ResponseWriter, r *http.Request, proj
 		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,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 {
@@ -361,10 +349,6 @@ 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)
 }
diff --git a/internal/platform/canvas_capabilities.go b/internal/platform/canvas_capabilities.go
index ad8970a..694e19b 100644
--- a/internal/platform/canvas_capabilities.go
+++ b/internal/platform/canvas_capabilities.go
@@ -39,7 +39,7 @@ func (s *service) canvasCapabilities(w http.ResponseWriter, r *http.Request, pro
 			}
 		}
 	}
-	ai := response{"canonical_target_identity": true, "admission_protocol_version": 2, "admission_receipt_query": true, "available": textAvailable || imageAvailable, "text": textAvailable, "image": imageAvailable}
+	ai := response{"canonical_target_identity": 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"
 	}