P2-04: coalesce facade autosaves

src/facade/index.ts

@@ -1,5 +1,5 @@
 export { createMockFacade } from './mockFacade'
-export { createSqliteProjectPersistence, PersistenceWriteQueue, SqliteProjectPersistence } from './projectStore'
+export { createSqliteProjectPersistence, PersistenceWriteQueue, ProjectAutosaveScheduler, SqliteProjectPersistence } from './projectStore'
 export { ThreeViewportAdapter } from './threeViewport'
 export { PROJECT_SCHEMA_MIGRATIONS, PROJECT_SCHEMA_SQL, PROJECT_SCHEMA_VERSION } from './projectSchema'
 export type { BitBybitWebCadFacade, CommandState, DocumentSnapshot, FacadeEvent, FacadeState, ModelTreeItem, PersistenceCapabilities, ProjectResource, ProjectSaveResult, TaskSnapshot } from './types'

src/facade/mockFacade.ts

@@ -13,7 +13,7 @@ import type {
   TaskSnapshot,
   Unsubscribe,
 } from './types'
-import { createSqliteProjectPersistence } from './projectStore'
+import { createSqliteProjectPersistence, ProjectAutosaveScheduler } from './projectStore'
 import { ThreeViewportAdapter } from './threeViewport'
 
 const initialTree: ModelTreeItem[] = [
@@ -51,6 +51,7 @@ const commandState = (commandId: string, activeWorkbench: WorkbenchId, selectedO
 
 export function createMockFacade(): BitBybitWebCadFacade {
   const projectPersistence = createSqliteProjectPersistence()
+  const autosave = new ProjectAutosaveScheduler((document) => projectPersistence.save(document))
   let state: FacadeState = { apiVersion: '0.1', activeWorkbench: 'Part Design', selectedObjectId: 'pad', document: createDocument(), persistence: projectPersistence.capabilities(), task: null, lastNotice: '', diagnostics: [] }
   const listeners = new Set<FacadeListener>()
   const undoStack: FacadeState[] = []
@@ -60,7 +61,7 @@ export function createMockFacade(): BitBybitWebCadFacade {
   const emit = (event: FacadeEvent) => listeners.forEach((listener) => listener(event))
   const emitState = () => emit({ type: 'state.changed', state: getState() })
   const getState = () => ({ ...state, diagnostics: state.diagnostics.map((diagnostic) => ({ ...diagnostic })), document: { ...state.document, tree: state.document.tree.map((item) => ({ ...item, children: item.children ? [...item.children] : undefined })) }, task: state.task ? { ...state.task, draft: { ...state.task.draft } } : null })
-  const commit = (next: FacadeState) => { undoStack.push(getState()); redoStack.length = 0; state = next; emitState() }
+  const commit = (next: FacadeState) => { undoStack.push(getState()); redoStack.length = 0; state = next; if (next.document.dirty) autosave.schedule(next.document); emitState() }
   const notify = (message: string) => { state = { ...state, lastNotice: message }; emit({ type: 'notice', message }); emitState() }
   const setActive = (id: WorkbenchId) => { state = { ...state, activeWorkbench: id }; emitState(); notify(`${id} workbench loaded`) }
   const select = (objectId: string) => { state = { ...state, selectedObjectId: objectId }; emitState() }

src/facade/projectStore.ts

@@ -35,6 +35,35 @@ export class PersistenceWriteQueue {
   }
 }
 
+export class ProjectAutosaveScheduler {
+  private timer: ReturnType<typeof setTimeout> | null = null
+  private pending: DocumentSnapshot | null = null
+  private flushPromise: Promise<ProjectSaveResult | null> | null = null
+
+  constructor(private readonly save: (document: DocumentSnapshot) => Promise<ProjectSaveResult>, private readonly idleMs = 800) {}
+
+  schedule(document: DocumentSnapshot) {
+    this.pending = cloneDocument(document)
+    if (this.timer) clearTimeout(this.timer)
+    this.timer = setTimeout(() => { this.timer = null; void this.flush() }, this.idleMs)
+  }
+
+  flush() {
+    if (this.flushPromise) return this.flushPromise
+    const document = this.pending
+    this.pending = null
+    if (!document) return Promise.resolve(null)
+    this.flushPromise = this.save(document).finally(() => { this.flushPromise = null; if (this.pending) void this.flush() })
+    return this.flushPromise
+  }
+
+  cancel() {
+    if (this.timer) clearTimeout(this.timer)
+    this.timer = null
+    this.pending = null
+  }
+}
+
 export class SqliteProjectPersistence implements ProjectPersistenceClient {
   private readonly worker: Worker | null
   private nextRequestId = 0