import type { Document, Id, Registry, Result, RunInput, RunApplyInput, RunCancelInput, Json, OperationIntent, Data } from '../canvas-core/types.ts';
import { createEditor, type EditorOptions, type Transaction } from '../canvas-core/editor.ts';
import { createDocument } from '../canvas-core/document.ts';
import { createSessions } from '../canvas-core/gestures.ts';
import { equal, fault, freeze, readMap, reject } from '../canvas-core/values.ts';
import type { EngineSnapshot, PersistencePort, RuntimeState } from './contracts.ts';
import { createRunTracker, validateRunInput, runContainsTarget, type RunPort, type RunRecord, type RunPage } from './runs.ts';
import { createNetworkGate } from './network.ts';
import { createLedger, type FrozenRequest } from './ledger.ts';
import { operationCanvases, replayPending } from './reconcile.ts';
import { decodeRecovery, encodeRecovery } from './recovery.ts';
import { createScheduler, type Clock, type OperationStatus } from './scheduler.ts';
import { conflictsWith, maxResourceBytes, operationFootprint, referencedResources, type AssetPort, type ResourceRecord, type ResourceHandle, type StagedFile } from './resources.ts';
import type { StoragePort, StorageScope } from './storage.ts';

export type EngineOptions = {
  scope: StorageScope; registry: Registry; document: Document; versions: ReadonlyMap<Id, number>;
  storage: StoragePort; persistence: PersistencePort; assets?: AssetPort; runs?: RunPort; createId?: () => Id;
  historyLimit?: number; policy?: EditorOptions['policy']; traversalPolicy?: EditorOptions['traversalPolicy']; clock?: Clock;
  onError?: (error: unknown) => void;
};

/** One project owner. Detaching a view does not close this engine or abort persistent work. */
export async function openProjectEngine(options: EngineOptions) {
  if (options.scope.projectId !== options.document.projectId) throw fault('project_mismatch');
  const leader = await options.storage.claim(options.scope);
  try {
    const image = await options.storage.recover(leader), recovered = image ? decodeRecovery(image, options.registry) : undefined;
    if (recovered && recovered.document.projectId !== options.scope.projectId) throw fault('project_mismatch');
    for (const canvas of options.document.canvases.keys()) if (!Number.isSafeInteger(options.versions.get(canvas)) || options.versions.get(canvas)! < 1) throw fault('missing_server_version', [canvas]);
    let closing = false, closed = false, durableRootRevision = image?.rootRevision ?? -1;
    const report = (error: unknown) => { try { options.onError?.(error); } catch { /* Error reporting cannot alter state. */ } };
    const createId = options.createId ?? (() => crypto.randomUUID());
    const network = createNetworkGate(2);
    const runClock: Clock = options.clock ?? { now: () => Date.now(), setTimer: (fn, delay) => setTimeout(fn, delay), clearTimer: handle => clearTimeout(handle as ReturnType<typeof setTimeout>) };
    const displays = new Set<() => void>();
    const fileWrites = new Map<Id, Blob>(), digestTasks = new Map<Id, Promise<void>>();
    let staged: readonly ResourceRecord[] = [];
    let applying: RunApplyInput | undefined;
    const initial: RuntimeState = recovered?.runtime ?? Object.freeze({ runs: readMap(new Map()), acknowledged: createDocument(options.document.projectId, [...options.document.canvases.values()], [...options.document.elements.values()], options.document.tombstones), versions: readMap(options.versions), ledger: createLedger().getSnapshot(), receipts: readMap(new Map()), conflicts: readMap(new Map()), resources: readMap(new Map()), resourcePins: readMap(new Map()) });
    const editor = createEditor({ registry: options.registry, document: options.document, recovery: recovered, runtime: initial, createId: options.createId, historyLimit: options.historyLimit,
      policy(command, document) { if (closing || closed) return { enabled: false, code: 'engine_closing', targets: [] }; return options.policy?.(command, document) ?? { enabled: true }; },
      traversalPolicy(entry, direction) { return closing || closed ? { enabled: false, code: 'engine_closing', targets: [] } : options.traversalPolicy?.(entry, direction) ?? { enabled: true }; },
      onListenerError: report,
      prepareIntent: intent => applying && intent.origin==='user' ? {...intent,operationType:'run.apply',action:applying} : intent,
      nextOperationSequence(runtime, fallback) { let next = fallback; for (const record of runtime.ledger.operations.values()) next = Math.max(next, record.intent.sequence + 1); return next + staged.length; },
      reduceRuntime(previous, next, commit) {
        if (!commit.operationIds.length) return previous;
        const ledger = createLedger(previous.ledger), resources = new Map(previous.resources);
        const firstSequence = next.operations.get(commit.operationIds[0])!.sequence - staged.length;
        staged.forEach((resource, index) => {
          if (resources.has(resource.id) || ledger.getSnapshot().operations.has(resource.operationId)) throw fault('resource_identity_conflict', [resource.id]);
          resources.set(resource.id, resource);
          ledger.add(freeze({ id: resource.operationId, operationType: 'asset.upload', operationSchemaVersion: 1, sequence: firstSequence + index, origin: 'user', canvasIds: [], changes: [], dependencies: [], resourceId: resource.id }), {});
          ledger.block(resource.operationId, ['waiting_digest']);
        });
        for (const id of commit.operationIds) {
          const intent = next.operations.get(id)!, footprint = operationFootprint(intent, next.document);
          const dependencies = new Set(intent.dependencies);
          for (const record of ledger.getSnapshot().operations.values()) if (record.phase !== 'resolved' && (record.intent.operationType === 'run.start' || ['document.change','run.apply'].includes(record.intent.operationType) && conflictsWith(operationFootprint(record.intent, next.document), footprint))) dependencies.add(record.intent.id);
          for (const id of referencedResources(intent.changes, options.registry)) {
            const resource = resources.get(id);
            if (resource && !resource.stored) dependencies.add(resource.operationId);
          }
          const basePresence: Record<Id, 'absent' | 'exists'> = Object.create(null);
          for (const change of intent.changes) if (change.kind === 'element') basePresence[change.id] = change.before ? 'exists' : 'absent'; else if (change.kind === 'field') basePresence[change.target.id] ??= 'exists';
          ledger.add(freeze({ ...intent, dependencies: [...dependencies] }), basePresence);
        }
        return Object.freeze({ ...previous, resources: readMap(resources), ledger: ledger.getSnapshot() });
      },
    });
    const pending = new Map<number, EngineSnapshot>();
    if (!recovered) pending.set(editor.getSnapshot().rootRevision, editor.getSnapshot());
    let writing: Promise<void> | undefined, scheduled = false;
    function persist(): Promise<void> {
      if (writing) return writing;
      const task = (async () => {
        while (pending.size) {
          const [revision, snapshot] = pending.entries().next().value!;
          const files = [...fileWrites].filter(([id]) => snapshot.runtime.resources.has(id)).map(([id, bytes]) => ({ id, bytes }));
          const receipt = await options.storage.commit(leader, { image: encodeRecovery(snapshot), files });
          if (receipt.durableRootRevision !== revision) throw fault('invalid_durable_receipt');
          durableRootRevision = revision; pending.delete(revision);
          for (const file of files) fileWrites.delete(file.id);
          if (editor.getSnapshot().runtime.ledger.durableGeneration < snapshot.runtime.ledger.generation) mutate(ledger => ledger.markDurable(snapshot.runtime.ledger.generation));
        }
      })();
      writing = task.finally(() => { writing = undefined; });
      return writing;
    }
    function mutate(reduce: (ledger: ReturnType<typeof createLedger>) => void) {
      const result = editor.updateRuntime(previous => { const ledger = createLedger(previous.ledger); reduce(ledger); return Object.freeze({ ...previous, ledger: ledger.getSnapshot() }); });
      if (result.status === 'rejected') throw fault(result.code, result.targets);
    }
    function complete(request: FrozenRequest, status: OperationStatus): { readonly blocked: true } | void {
      const root = editor.getSnapshot(), previous = root.runtime, ledger = createLedger(previous.ledger);
      if (request.phase === 'resolved') return;
      if (status.outcome !== 'applied') {
        const result=editor.updateRuntime(runtime=>{const ledger=createLedger(runtime.ledger),receipts=new Map(runtime.receipts);ledger.result(request.id,status.outcome,status.error);if(status.outcome==='not-applied'&&['run.start','run.cancel'].includes(request.kind??''))ledger.resolveNoEffect(request.id);if(status.canonical!==undefined)receipts.set(request.id,freeze(status.canonical));return Object.freeze({...runtime,ledger:ledger.getSnapshot(),receipts:readMap(receipts)});},root.rootRevision);
        if(result.status==='rejected')throw fault(result.code,result.targets);return;
      }
      if(request.kind==='run.cancel'){
        const receipts=new Map(previous.receipts);if(status.canonical!==undefined)receipts.set(request.id,freeze(status.canonical));
        try{
          if(!options.runs)throw fault('run_interpreter_unavailable');
          const accepted=options.runs.acceptAction(request,status,root),run=previous.runs.get(accepted.runId);if(!run||!accepted.runStatus)throw fault('run_identity_mismatch');
          ledger.result(request.id,'applied');const runs=new Map(previous.runs);runs.set(run.id,freeze({...run,controlEpoch:(run.controlEpoch??0)+1,status:accepted.runStatus,hasMore:true,blocked:false,error:undefined,nextPollAt:runClock.now()}));
          const result=editor.updateRuntime(()=>Object.freeze({...previous,runs:readMap(runs),receipts:readMap(receipts),ledger:ledger.getSnapshot()}),root.rootRevision);if(result.status==='rejected')throw fault(result.code,result.targets);
          queueMicrotask(()=>runTracker.notify([run.id]));return;
        }catch(error){ledger.result(request.id,'applied',(error as Error).message,false);const result=editor.updateRuntime(()=>Object.freeze({...previous,receipts:readMap(receipts),ledger:ledger.getSnapshot()}),root.rootRevision);if(result.status==='rejected')throw fault(result.code,result.targets);report(error);return{blocked:true};}
      }
      if (request.kind === 'asset.upload') {
        const receipts = new Map(previous.receipts); if (status.canonical !== undefined) receipts.set(request.id, freeze(status.canonical));
        try {
          const intent = previous.ledger.operations.get(request.operationIds[0])?.intent;
          if (intent?.operationType !== 'asset.upload' || !options.assets) throw fault('asset_interpreter_unavailable');
          const resource = previous.resources.get(intent.resourceId);
          if (!resource) throw fault('resource_missing');
          const stored = freeze(options.assets.accept(request, status, resource));
          if (stored.id !== resource.id || stored.bytes !== resource.byteLength) throw fault('asset_receipt_mismatch');
          ledger.result(request.id, 'applied');
          const resources = new Map(previous.resources); resources.set(resource.id, freeze({ ...resource, stored }));
          const result = editor.updateRuntime(() => Object.freeze({ ...previous, receipts: readMap(receipts), resources: readMap(resources), ledger: ledger.getSnapshot() }), root.rootRevision);
          if (result.status === 'rejected') throw fault(result.code, result.targets);
          return;
        } catch (error) {
          ledger.result(request.id, 'applied', (error as Error).message, false);
          const result = editor.updateRuntime(() => Object.freeze({ ...previous, receipts: readMap(receipts), ledger: ledger.getSnapshot() }), root.rootRevision);
          if (result.status === 'rejected') throw fault(result.code, result.targets);
          report(error); return { blocked: true };
        }
      }
      const receipts = new Map(previous.receipts), conflicts = new Map(previous.conflicts);
      if (status.canonical !== undefined) receipts.set(request.id, freeze(status.canonical));
      try {
        const action = request.kind==='run.apply' ? options.runs?.acceptAction(request,status,root) : undefined;
        if(request.kind==='run.apply'&&!action?.proposal)throw fault('run_interpreter_unavailable');
        const admission = request.kind === 'run.start' ? options.runs?.accept(request, status, root) : undefined;
        if (request.kind === 'run.start' && !admission) throw fault('run_interpreter_unavailable');
        const proposal = action?.proposal ?? admission?.proposal ?? options.persistence.canonical(request, status, root);
        const writtenCanvases = admission ? [request.ownerCanvasId!] : request.canvasIds;
        if (proposal.document.projectId !== root.document.projectId) throw fault('project_mismatch');
        for (const canvas of writtenCanvases) {
          const version = proposal.versions.get(canvas);
          if (!version || version <= request.expectedVersions[canvas] || version < (previous.versions.get(canvas) ?? 0)) throw fault('stale_canonical_version', [canvas]);
        }
        // A codec cannot roll back an unrelated canvas while reconciling this request.
        for (const [canvas, version] of previous.versions) if (!writtenCanvases.includes(canvas)) {
          if (proposal.versions.get(canvas) !== version || !equal(proposal.document.canvases.get(canvas), previous.acknowledged.canvases.get(canvas)) || !equal([...proposal.document.elements.values()].filter(element => element.ownerCanvasId === canvas), [...previous.acknowledged.elements.values()].filter(element => element.ownerCanvasId === canvas))) throw fault('canonical_scope_mismatch', [canvas]);
        }
        ledger.result(request.id, 'applied');
        const acknowledged = createDocument(proposal.document.projectId, [...proposal.document.canvases.values()], [...proposal.document.elements.values()], proposal.document.tombstones);
        const document = replayPending(acknowledged, ledger.getSnapshot(), options.registry);
        conflicts.delete(request.id);
        const runs = new Map(previous.runs);
        if (admission) {
          const existing = runs.get(admission.run.id);
          if (existing && (existing.requestId !== request.id || existing.operationId !== admission.run.operationId)) throw fault('run_identity_mismatch');
          if (!existing) runs.set(admission.run.id, admission.run);
        }
        if(action){const run=runs.get(action.runId);if(!run)throw fault('run_identity_mismatch');runs.set(run.id,freeze({...run,controlEpoch:(run.controlEpoch??0)+1,appliedOutputIds:[...new Set([...(run.appliedOutputIds??[]),action.outputId!])],hasMore:true,blocked:false,error:undefined,pendingPage:undefined,nextPollAt:runClock.now()}));}
        const runtime: RuntimeState = Object.freeze({ ...previous, runs: readMap(runs), ledger: ledger.getSnapshot(), acknowledged, versions: readMap(proposal.versions), receipts: readMap(receipts), conflicts: readMap(conflicts) });
        const result = editor.reconcile(document, runtime, root.rootRevision);
        if (result.status === 'rejected') throw fault(result.code, result.targets);
        if(action)queueMicrotask(()=>runTracker.notify([action.runId]));
      } catch (error) {
        // Preserve both the known receipt and the user's working document. No rollback or lane release.
        const waiting = createLedger(previous.ledger); waiting.result(request.id, 'applied', (error as Error).message, false);
        conflicts.set(request.id, (error as Error).message || 'reconcile_conflict');
        const result = editor.updateRuntime(() => Object.freeze({ ...previous, ledger: waiting.getSnapshot(), receipts: readMap(receipts), conflicts: readMap(conflicts) }), root.rootRevision);
        if (result.status === 'rejected') throw fault(result.code, result.targets);
        report(error); return { blocked: true };
      }
    }
    const scheduler = createScheduler({ getLedger: () => editor.getSnapshot().runtime.ledger, mutate, persist,
      createId: options.createId ?? (() => crypto.randomUUID()),
      participants: intent => operationCanvases(intent, editor.getSnapshot().document),
      compile(intent, id) {
        if (intent.operationType === 'document.change') return options.persistence.compile(intent, id, editor.getSnapshot());
        if (['run.start','run.cancel','run.apply'].includes(intent.operationType)) { if (!options.runs) throw fault('run_interpreter_unavailable');return options.runs.compile(intent,id,editor.getSnapshot()); }
        if(intent.operationType!=='asset.upload')throw fault('operation_interpreter_unavailable');
        const resource = editor.getSnapshot().runtime.resources.get(intent.resourceId);
        if (!options.assets || !resource?.digest) throw fault('asset_not_ready');
        return { kind: 'asset.upload', protocolVersion: 2, canvasIds: [], expectedVersions: {}, payload: { protocol_version: 2, request_id: id, resource_id: resource.id, operation_id: resource.operationId, sha256: resource.digest, byte_length: resource.byteLength, name: resource.name, mime_type: resource.mimeType } };
      },
      async submit(request, signal) {
        if (['run.start','run.cancel','run.apply'].includes(request.kind??'')) return options.runs ? network.run(signal, () => options.runs!.submit(request,signal)) : { outcome: 'unresolved', blocked: true, error: 'run_interpreter_unavailable' };
        if (request.kind !== 'asset.upload') return network.run(signal, () => options.persistence.submit(request, signal));
        if (!options.assets) return { outcome: 'unresolved', blocked: true, error: 'asset_interpreter_unavailable' };
        const payload = JSON.parse(request.body), bytes = await options.storage.readFile(leader, payload.resource_id);
        if (!bytes || bytes.size !== payload.byte_length || await digest(bytes) !== payload.sha256) return { outcome: 'unresolved', blocked: true, error: 'resource_bytes_unavailable' };
        return network.run(signal, () => options.assets!.upload(request, bytes, signal));
      },
      query: (request, signal) => network.run(signal, () => ['run.start','run.cancel','run.apply'].includes(request.kind??'') ? options.runs?.query(request,signal) ?? Promise.resolve({ outcome: 'unresolved', blocked: true, error: 'run_interpreter_unavailable' }) : request.kind === 'asset.upload' ? options.assets?.query(request, signal) ?? Promise.resolve({ outcome: 'unresolved', blocked: true, error: 'asset_interpreter_unavailable' }) : options.persistence.query(request, signal)),
      supportsRequest: request => ['run.start','run.cancel','run.apply'].includes(request.kind??'') ? !!options.runs && request.protocolVersion === 2 : request.kind === 'asset.upload' ? !!options.assets && request.protocolVersion === 2 : options.persistence.supportsRequest?.(request) ?? request.protocolVersion === 1, complete, onError: report, clock: options.clock,
    });
    function updateRun(id: Id, reduce: (run: RunRecord) => RunRecord) {
      const result = editor.updateRuntime(previous => { const current = previous.runs.get(id);if(!current)throw fault('run_missing');const runs = new Map(previous.runs);runs.set(id,freeze(reduce(current)));return Object.freeze({...previous,runs:readMap(runs)}); });
      if(result.status==='rejected')throw fault(result.code,result.targets);
    }
    function acceptRunPage(run: RunRecord, page: RunPage) {
      const root=editor.getSnapshot(),previous=root.runtime,current=previous.runs.get(run.id);
      if(!current || current.requestId!==run.requestId)throw fault('run_identity_mismatch');
      if((current.controlEpoch??0)!==(run.controlEpoch??0))return;
      if(current.cursor!==run.cursor)throw fault('run_identity_mismatch');
      const outputEvents=new Map(current.outputEvents.map(event=>[event.step_id,event]));
      for(const event of page.events)if(event.type==='step.output')outputEvents.set(event.step_id,event);
      let acknowledged=previous.acknowledged,versions=previous.versions;
      const conflicts=new Map(previous.conflicts);
      try {
        for(const event of page.events) {
          if(event.seq<=current.cursor || event.type!=='step.applied'&&!(event.type==='step.output'&&event.model&&typeof event.model==='object'&&!Array.isArray(event.model)&&event.model.complete===true))continue;
          const canvas=event.board_id as Id,version=event.canvas_version as number;
          if(!Number.isSafeInteger(version)||version<1)throw fault('invalid_run_response');
          // A later document receipt already includes this event; never rewind its participant.
          if(version<=(versions.get(canvas)??0))continue;
          const model=event.model as {[key:string]:Json}|undefined,context=model?.complete===true,participants=context?Object.keys(model.versions as {[key:string]:Json}):[canvas];
          if([...previous.ledger.requests.values()].some(request=>request.phase!=='resolved'&&request.canvasIds.some(id=>participants.includes(id))))throw fault('run_waiting_for_receipts');
          if(!options.runs)throw fault('run_interpreter_unavailable');
          const snapshot={...root,runtime:{...previous,acknowledged,versions}};
          const proposal=options.runs.canonical(event,snapshot);
          for(const record of previous.ledger.operations.values())if(record.phase!=='resolved')for(const change of record.intent.changes)if(change.kind==='field'&&(change.field==='geometry'||change.field==='path')){const before=acknowledged.elements.get(change.target.id),after=proposal.document.elements.get(change.target.id);if(before&&after&&before.ownerCanvasId!==after.ownerCanvasId)throw fault('ownership_conflict',[change.target.id]);}
          acknowledged=proposal.document;versions=proposal.versions;
        }
        const document=replayPending(acknowledged,previous.ledger,options.registry),runs=new Map(previous.runs);
        const appliedOutputIds=[...new Set([...(current.appliedOutputIds??[]),...page.events.filter(event=>event.type==='step.applied'&&typeof event.output_id==='string').map(event=>event.output_id as Id)])];
        runs.set(run.id,freeze({...current,appliedOutputIds,cursor:page.next,status:page.status,hasMore:page.hasMore,outputs:page.outputs,outputEvents:[...outputEvents.values()],steps:page.steps,error:page.error,blocked:false,pendingPage:undefined}));
        conflicts.delete(`run:${run.id}`);
        const result=editor.reconcile(document,Object.freeze({...previous,acknowledged,versions:readMap(versions),runs:readMap(runs),conflicts:readMap(conflicts)}),root.rootRevision);
        if(result.status==='rejected')throw fault(result.code,result.targets);
      } catch(error) {
        const code=(error as Error).message;
        // Save the page as evidence without overwriting local content or advancing the cursor.
        const result=editor.updateRuntime(runtime=>{const runs=new Map(runtime.runs);runs.set(run.id,freeze({...current,outputs:page.outputs,outputEvents:[...outputEvents.values()],steps:page.steps,pendingPage:page,error:code,blocked:code!=='run_waiting_for_receipts'}));if(code!=='run_waiting_for_receipts')conflicts.set(`run:${run.id}`,code);return Object.freeze({...runtime,runs:readMap(runs),conflicts:readMap(conflicts)});},root.rootRevision);
        if(result.status==='rejected')throw fault(result.code,result.targets);
        if(code!=='run_waiting_for_receipts')report(error);
      }
    }
    const runTracker=createRunTracker({clock:runClock,getRuns:()=>editor.getSnapshot().runtime.runs,persist,update:updateRun,accept:acceptRunPage,
      poll:(run,signal)=>options.runs ? network.run(signal,()=>options.runs!.poll(run,signal)) : Promise.reject(fault('run_interpreter_unavailable')),onError:report});
    const trackedRuns=new Set(initial.runs.keys());
    const sessions = createSessions(editor);
    const unsubscribe = editor.subscribe((commit, snapshot) => {
      pending.set(snapshot.rootRevision, snapshot);
      const addedRuns=[...snapshot.runtime.runs.keys()].filter(id=>!trackedRuns.has(id));for(const id of addedRuns)trackedRuns.add(id);
      if(addedRuns.length)queueMicrotask(()=>runTracker.notify(addedRuns));
      if (!scheduled) { scheduled = true; queueMicrotask(() => { scheduled = false; void persist().catch(report); }); }
      // Intents already exist in this root; notification only schedules their IDs.
      const operationIds = [...commit.operationIds, ...staged.map(resource => resource.operationId)];
      queueMicrotask(() => { if (!closing && !closed) { scheduler.notify(operationIds); if (operationIds.length) prepareDigests(); } });
    });
    async function digest(bytes: Blob) { return [...new Uint8Array(await crypto.subtle.digest('SHA-256', await bytes.arrayBuffer()))].map(value => value.toString(16).padStart(2, '0')).join(''); }
    function prepareDigests() {
      if (closing || closed) return;
      for (const resource of editor.getSnapshot().runtime.resources.values()) {
        if (digestTasks.size >= 2) break;
        if (resource.digest || digestTasks.has(resource.id)) continue;
        const operation = editor.getSnapshot().runtime.ledger.operations.get(resource.operationId);
        if (operation?.phase !== 'blocked' || !operation.blockers.includes('waiting_digest')) continue;
        const task = Promise.resolve().then(async () => {
          const bytes = fileWrites.get(resource.id) ?? await options.storage.readFile(leader, resource.id);
          if (!bytes || bytes.size !== resource.byteLength) throw fault('resource_bytes_unavailable', [resource.id]);
          const hash = await digest(bytes);
          if (closing || closed) return;
          const result = editor.updateRuntime(previous => {
            if (previous.resources.get(resource.id) !== resource) throw fault('resource_identity_conflict', [resource.id]);
            const resources = new Map(previous.resources), ledger = createLedger(previous.ledger);
            resources.set(resource.id, freeze({ ...resource, digest: hash })); ledger.block(resource.operationId, []);
            return Object.freeze({ ...previous, resources: readMap(resources), ledger: ledger.getSnapshot() });
          });
          if (result.status === 'rejected') throw fault(result.code, result.targets);
          scheduler.notify([resource.operationId]);
        }).catch(error => { if (!closing && !closed) { mutate(ledger => ledger.block(resource.operationId, ['resource_bytes_unavailable'])); report(error); } }).finally(() => { digestTasks.delete(resource.id); prepareDigests(); });
        digestTasks.set(resource.id, task);
      }
    }
    function queueRunAction(operationType:'run.cancel'|'run.apply',action:RunCancelInput|RunApplyInput):Result {
      const root=editor.getSnapshot();let sequence=1;for(const record of root.runtime.ledger.operations.values())sequence=Math.max(sequence,record.intent.sequence+1);
      const id=createId(),intent={id,operationType,action,operationSchemaVersion:1,sequence,origin:'user',canvasIds:operationType==='run.apply'?[(action as RunApplyInput).targetCanvasId]:[],changes:[],dependencies:operationType==='run.cancel'?[]:[...root.runtime.ledger.operations.values()].filter(record=>record.phase!=='resolved').map(record=>record.intent.id)} as OperationIntent;
      const result=editor.updateRuntime(previous=>{const ledger=createLedger(previous.ledger);ledger.add(freeze(intent),{});return Object.freeze({...previous,ledger:ledger.getSnapshot()});},root.rootRevision);
      if(result.status==='rejected')return result;queueMicrotask(()=>{if(!closing&&!closed)scheduler.notify([id]);});return{status:'applied',revision:root.revision,operationIds:[id]};
    }
    scheduler.start(); prepareDigests(); runTracker.notify([...initial.runs.keys()]);
    return Object.freeze({
      editor, sessions,
      models(boardId: Id, signal: AbortSignal) {
        if(closing||closed||!options.runs)return Promise.reject(fault('run_interpreter_unavailable'));
        if(!editor.getSnapshot().document.canvases.has(boardId))return Promise.reject(fault('canvas_missing'));
        return network.run(signal,()=>options.runs!.catalog(boardId,signal));
      },
      cancelRun(runId:Id):Result {
        try{
          if(closing||closed)throw fault('engine_closing');if(!options.runs)throw fault('run_interpreter_unavailable');
          const root=editor.getSnapshot(),run=root.runtime.runs.get(runId);if(!run)throw fault('run_missing');
          const allowed=options.policy?.({type:'element.data',target:run.target,patch:{}},root.document);if(allowed&&!allowed.enabled)throw fault(allowed.code,allowed.targets);
          if([...root.runtime.ledger.operations.values()].some(record=>record.phase!=='resolved'&&record.intent.operationType==='run.cancel'&&record.intent.action.runId===runId))throw fault('run_action_pending');
          return queueRunAction('run.cancel',{runId,boardId:run.boardId});
        }catch(error){return reject(error);}
      },
      applyRunOutput(runId:Id,target:RunApplyInput['target'],outputId:Id):Result {
        try{
          if(closing||closed)throw fault('engine_closing');if(!options.runs)throw fault('run_interpreter_unavailable');if(applying)throw fault('reentrant_dispatch');
          const root=editor.getSnapshot(),run=root.runtime.runs.get(runId),element=root.document.elements.get(target.id);
          if(!run||run.blocked||!runContainsTarget(run,target)||!element||element.incarnation!==target.incarnation)throw fault('target_changed');
          if((run.appliedOutputIds??[]).includes(outputId))throw fault('output_already_applied');
          if([...root.runtime.ledger.operations.values()].some(record=>record.phase!=='resolved'&&(record.intent.operationType==='run.apply'||record.intent.operationType==='run.cancel')&&record.intent.action.runId===runId))throw fault('run_action_pending');
          const event=run.outputEvents.find(event=>event.node_id===target.id&&event.output&&typeof event.output==='object'&&!Array.isArray(event.output)&&event.output.output_id===outputId),output=event?.output as {[key:string]:Json}|undefined;
          if(!output||run.status!=='conflict')throw fault('output_not_applicable');
          const patch:Data|undefined=output.kind==='text'&&typeof output.text==='string'?{text:output.text}:output.kind==='image'&&typeof output.src==='string'&&typeof output.assetId==='string'?{src:output.src,assetId:output.assetId}:undefined;if(!patch)throw fault('invalid_run_output');
          const action:RunApplyInput={runId,boardId:run.boardId,targetCanvasId:element.ownerCanvasId,target,outputId};applying=action;
          const result=editor.dispatch({type:'element.data',target,patch},{label:'Apply generated result'});
          if(result.status==='rejected'||result.operationIds.length)return result;
          return queueRunAction('run.apply',action);
        }catch(error){return reject(error);}finally{applying=undefined;}
      },
      startRun(input: RunInput): Result {
        try {
          if(closing||closed)throw fault('engine_closing');
          if(!options.runs)throw fault('run_interpreter_unavailable');
          validateRunInput(input);
          const root=editor.getSnapshot(),element=root.document.elements.get(input.target.id);
          if(!element||element.incarnation!==input.target.incarnation||element.ownerCanvasId!==input.boardId||element.structure!=='node'||options.registry.resolve(element)!=='known'||!['text','plain-text','script','image','plain-image'].includes(element.componentId))throw fault('target_changed');
          const allowed=editor.can({type:'element.data',target:input.target,patch:{ai:{enabled:true,modelId:input.modelId,prompt:input.prompt,parameters:input.parameters,propagate:input.propagate}}});
          if(!allowed.enabled)throw fault(allowed.code,allowed.targets);
          if([...root.runtime.ledger.operations.values()].some(record=>record.intent.operationType==='run.start'&&record.phase!=='resolved'&&record.intent.run.target.id===input.target.id))throw fault('node_busy');
          if([...root.runtime.runs.values()].some(run=>runContainsTarget(run,input.target)&&(run.hasMore||run.pendingPage||['queued','running'].includes(run.status))))throw fault('node_busy');
          const id=createId(),dependencies=[...root.runtime.ledger.operations.values()].filter(record=>record.phase!=='resolved').map(record=>record.intent.id);
          let sequence=1;for(const record of root.runtime.ledger.operations.values())sequence=Math.max(sequence,record.intent.sequence+1);
          const result=editor.updateRuntime(previous=>{const ledger=createLedger(previous.ledger);ledger.add(freeze({id,operationType:'run.start',operationSchemaVersion:1,sequence,origin:'user',canvasIds:[...root.document.canvases.keys()].sort(),changes:[],dependencies,run:JSON.parse(JSON.stringify(input))}),{});return Object.freeze({...previous,ledger:ledger.getSnapshot()});},root.rootRevision);
          if(result.status==='rejected')return result;
          queueMicrotask(()=>{if(!closing&&!closed)scheduler.notify([id]);});
          return{status:'applied',revision:root.revision,operationIds:[id]};
        }catch(error){return reject(error);}
      },
      refresh(document: Document, versions: ReadonlyMap<Id, number>): Result {
        const root = editor.getSnapshot(), previous = root.runtime;
        try {
          if (closing || closed) throw fault('engine_closing');
          if (document.projectId !== root.document.projectId) throw fault('project_mismatch');
          if ([...previous.ledger.requests.values()].some(request => request.phase !== 'resolved')) throw fault('refresh_waiting_for_receipts');
          for (const canvas of document.canvases.keys()) if (!Number.isSafeInteger(versions.get(canvas)) || versions.get(canvas)! < 1) throw fault('missing_server_version', [canvas]);
          for (const [id, version] of previous.versions) if ((versions.get(id) ?? -1) < version) throw fault('stale_canonical_version', [id]);
          if (equal([...previous.versions], [...versions]) && equal([...previous.acknowledged.canvases], [...document.canvases]) && equal([...previous.acknowledged.elements], [...document.elements]) && equal([...previous.acknowledged.tombstones], [...document.tombstones])) return { status: 'applied', revision: root.revision, operationIds: [] };
          const acknowledged = createDocument(document.projectId, [...document.canvases.values()], [...document.elements.values()], document.tombstones);
          const working = replayPending(acknowledged, previous.ledger, options.registry);
          const conflicts = new Map(previous.conflicts); conflicts.delete('refresh');
          return editor.reconcile(working, Object.freeze({ ...previous, acknowledged, versions: readMap(versions), conflicts: readMap(conflicts) }), root.rootRevision);
        } catch (error) {
          const result = reject(error);
          if (result.code !== 'refresh_waiting_for_receipts' && result.code !== 'engine_closing') editor.updateRuntime(previous => { const conflicts = new Map(previous.conflicts); conflicts.set('refresh', result.code); return Object.freeze({ ...previous, conflicts: readMap(conflicts) }); });
          return result;
        }
      },
      stageFiles(files: readonly StagedFile[], callback: (resources: readonly ResourceHandle[], transaction: Transaction) => unknown) {
        if (closing || closed) throw fault('engine_closing');
        if (staged.length) throw fault('reentrant_dispatch');
        if (!options.assets) throw fault('asset_interpreter_unavailable');
        const resources = files.map(file => {
          if (!(file.bytes instanceof Blob) || !file.bytes.size || file.bytes.size > maxResourceBytes || !file.bytes.type.startsWith('image/') || typeof file.name !== 'string' || !file.name) throw fault('invalid_staged_file');
          return freeze({ id: createId(), operationId: createId(), name: file.name, mimeType: file.bytes.type, byteLength: file.bytes.size });
        });
        if (new Set(resources.flatMap(resource => [resource.id, resource.operationId])).size !== resources.length * 2 || resources.some(resource => editor.getSnapshot().runtime.resources.has(resource.id) || fileWrites.has(resource.id))) throw fault('resource_identity_conflict');
        staged = resources; resources.forEach((resource, index) => fileWrites.set(resource.id, files[index].bytes));
        try {
          const handles = freeze(resources.map(resource => ({ id: resource.id, src: options.assets!.sourceURL(resource.id) })));
          const result = editor.transaction(tx => callback(handles, tx), { label: 'Add images' });
          if (result.status === 'rejected' || !result.operationIds.length) for (const resource of resources) fileWrites.delete(resource.id);
          return result;
        } finally { staged = []; for (const resource of resources) if (!editor.getSnapshot().runtime.resources.has(resource.id)) fileWrites.delete(resource.id); }
      },
      async displayResource(id: Id) {
        if (closing || closed) throw fault('engine_closing');
        const bytes = fileWrites.get(id) ?? await options.storage.readFile(leader, id);
        if (closing || closed) throw fault('engine_closing');
        if (!bytes && !options.assets) throw fault('resource_missing', [id]);
        const url = bytes ? URL.createObjectURL(bytes) : options.assets!.displayURL(id);
        let released = false;
        const release = () => { if (!released) { released = true; displays.delete(release); if (bytes) URL.revokeObjectURL(url); } };
        displays.add(release); return Object.freeze({ url, release });
      },
      getSnapshot: editor.getSnapshot, persist,
      getDurability: () => Object.freeze({ rootRevision: editor.getSnapshot().rootRevision, durableRootRevision }),
      retry: async () => { await scheduler.resume();await runTracker.retry(); },
      async settle() { await Promise.resolve(); while (digestTasks.size) await Promise.all([...digestTasks.values()]); await scheduler.settle(); await runTracker.settle(); await persist(); },
      async close() {
        if (closed) return;
        closing = true; sessions.dispose(); scheduler.stop(); runTracker.stop();
        for (const release of [...displays]) release();
        // Failure keeps the leader/recovery material available for an explicit retry of close.
        await persist(); unsubscribe(); editor.dispose(); await leader.release(); closed = true;
      },
    });
  } catch (error) { await leader.release(); throw error; }
}