P2-02: serialize persistence writes

src/facade/index.ts

@@ -1,5 +1,5 @@
 export { createMockFacade } from './mockFacade'
-export { createSqliteProjectPersistence, SqliteProjectPersistence } from './projectStore'
+export { createSqliteProjectPersistence, PersistenceWriteQueue, 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, ProjectSaveResult, TaskSnapshot } from './types'

src/facade/projectStore.ts

@@ -15,6 +15,21 @@ export interface ProjectPersistenceClient {
   dispose(): Promise<void>
 }
 
+/** Serializes persistence mutations while allowing reads to follow the write tail. */
+export class PersistenceWriteQueue {
+  private tail: Promise<void> = Promise.resolve()
+
+  run<T>(operation: () => Promise<T>): Promise<T> {
+    const next = this.tail.then(operation)
+    this.tail = next.then(() => undefined, () => undefined)
+    return next
+  }
+
+  drain(): Promise<void> {
+    return this.tail
+  }
+}
+
 export class SqliteProjectPersistence implements ProjectPersistenceClient {
   private readonly worker: Worker | null
   private nextRequestId = 0
@@ -22,6 +37,7 @@ export class SqliteProjectPersistence implements ProjectPersistenceClient {
   private initialized: Promise<PersistenceCapabilities> | null = null
   private readonly fallbackSnapshots = new Map<string, DocumentSnapshot>()
   private readonly pending = new Map<number, { resolve: (response: WorkerResponse) => void; reject: (error: Error) => void }>()
+  private readonly writeQueue = new PersistenceWriteQueue()
 
   constructor() {
     this.worker = typeof Worker === 'undefined' ? null : new Worker(new URL('./persistenceWorker.ts', import.meta.url), { type: 'module', name: 'bitbybit-persistence' })
@@ -40,15 +56,18 @@ export class SqliteProjectPersistence implements ProjectPersistenceClient {
     return this.initialized
   }
 
-  async save(document: DocumentSnapshot) {
-    await this.initialize()
-    if (!this.worker) { const snapshot = cloneDocument(document); this.fallbackSnapshots.set(snapshot.id, snapshot); return { documentId: snapshot.id, documentVersion: snapshot.version, persistedAt: Date.now(), mode: this.currentCapabilities.mode } }
-    const response = await this.request({ type: 'save-document', document })
-    if (!response.ok || response.type !== 'saved') throw new Error(response.ok ? 'Unexpected persistence response.' : response.error)
-    return { documentId: response.documentId, documentVersion: response.documentVersion, persistedAt: response.persistedAt, mode: response.mode }
+  save(document: DocumentSnapshot) {
+    return this.writeQueue.run(async () => {
+      await this.initialize()
+      if (!this.worker) { const snapshot = cloneDocument(document); this.fallbackSnapshots.set(snapshot.id, snapshot); return { documentId: snapshot.id, documentVersion: snapshot.version, persistedAt: Date.now(), mode: this.currentCapabilities.mode } }
+      const response = await this.request({ type: 'save-document', document })
+      if (!response.ok || response.type !== 'saved') throw new Error(response.ok ? 'Unexpected persistence response.' : response.error)
+      return { documentId: response.documentId, documentVersion: response.documentVersion, persistedAt: response.persistedAt, mode: response.mode }
+    })
   }
 
   async load(documentId: string) {
+    await this.writeQueue.drain()
     await this.initialize()
     if (!this.worker) { const snapshot = this.fallbackSnapshots.get(documentId); return snapshot ? cloneDocument(snapshot) : null }
     const response = await this.request({ type: 'load-document', documentId })
@@ -57,6 +76,7 @@ export class SqliteProjectPersistence implements ProjectPersistenceClient {
   }
 
   async dispose() {
+    await this.writeQueue.drain()
     if (!this.worker) return
     await this.request({ type: 'dispose' })
     this.worker.terminate()