Persist create-agent mode preferences reliably

packages/app/src/create-agent-preferences/service.ts

@@ -0,0 +1,62 @@
+import { AsyncStorageCreateAgentPreferenceStorage } from "./storage";
+import {
+  DEFAULT_FORM_PREFERENCES,
+  parseFormPreferences,
+  type FormPreferences,
+} from "./preferences";
+import type { CreateAgentPreferenceStorage } from "./storage";
+
+export type FormPreferenceUpdate =
+  | Partial<FormPreferences>
+  | ((current: FormPreferences) => FormPreferences);
+
+export class CreateAgentPreferencesService {
+  private preferences: FormPreferences = DEFAULT_FORM_PREFERENCES;
+  private isLoaded = false;
+  private loadPromise: Promise<FormPreferences> | null = null;
+  private writeQueue: Promise<void> = Promise.resolve();
+
+  constructor(private readonly storage: CreateAgentPreferenceStorage) {}
+
+  async load(): Promise<FormPreferences> {
+    if (this.isLoaded) {
+      return this.preferences;
+    }
+    if (!this.loadPromise) {
+      this.loadPromise = this.storage.read().then((stored) => {
+        this.preferences = parseFormPreferences(stored);
+        this.isLoaded = true;
+        return this.preferences;
+      });
+    }
+    return this.loadPromise;
+  }
+
+  async update(update: FormPreferenceUpdate): Promise<FormPreferences> {
+    const previousWrite = this.writeQueue;
+    const operation = this.applyQueuedUpdate(previousWrite, update);
+
+    this.writeQueue = operation.then(
+      () => undefined,
+      () => undefined,
+    );
+    return operation;
+  }
+
+  private async applyQueuedUpdate(
+    previousWrite: Promise<void>,
+    update: FormPreferenceUpdate,
+  ): Promise<FormPreferences> {
+    await previousWrite;
+    const current = await this.load();
+    const next = typeof update === "function" ? update(current) : { ...current, ...update };
+    this.preferences = parseFormPreferences(next);
+    this.isLoaded = true;
+    await this.storage.write(this.preferences);
+    return this.preferences;
+  }
+}
+
+export const createAgentPreferencesService = new CreateAgentPreferencesService(
+  new AsyncStorageCreateAgentPreferenceStorage(),
+);