fix: Buffer feature-flag subscribers registered before init

apps/code/src/renderer/utils/analytics.test.ts

@@ -0,0 +1,115 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const mockPosthog = {
+  init: vi.fn(),
+  register: vi.fn(),
+  onFeatureFlags: vi.fn(),
+  isFeatureEnabled: vi.fn(),
+  startSessionRecording: vi.fn(),
+  capture: vi.fn(),
+  identify: vi.fn(),
+  group: vi.fn(),
+  reset: vi.fn(),
+  captureException: vi.fn(),
+  reloadFeatureFlags: vi.fn(),
+};
+
+vi.mock("posthog-js/dist/module.full.no-external", () => ({
+  default: mockPosthog,
+}));
+
+vi.mock("posthog-js/dist/posthog-recorder", () => ({}));
+
+async function loadAnalytics() {
+  vi.resetModules();
+  return await import("./analytics");
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  vi.stubEnv("VITE_POSTHOG_API_KEY", "test-key");
+});
+
+afterEach(() => {
+  vi.unstubAllEnvs();
+});
+
+describe("onFeatureFlagsLoaded", () => {
+  it("delivers pre-init subscribers when init runs", async () => {
+    const { initializePostHog, onFeatureFlagsLoaded } = await loadAnalytics();
+
+    const cb = vi.fn();
+    onFeatureFlagsLoaded(cb);
+
+    expect(mockPosthog.onFeatureFlags).not.toHaveBeenCalled();
+
+    initializePostHog();
+
+    expect(mockPosthog.onFeatureFlags).toHaveBeenCalledTimes(1);
+    expect(mockPosthog.onFeatureFlags).toHaveBeenCalledWith(cb);
+  });
+
+  it("does not register a buffered listener that unsubscribed before init", async () => {
+    const { initializePostHog, onFeatureFlagsLoaded } = await loadAnalytics();
+
+    const cb = vi.fn();
+    const off = onFeatureFlagsLoaded(cb);
+    off();
+
+    initializePostHog();
+
+    expect(mockPosthog.onFeatureFlags).not.toHaveBeenCalled();
+  });
+
+  it("propagates unsubscribe to PostHog when called after init", async () => {
+    const realUnsub = vi.fn();
+    mockPosthog.onFeatureFlags.mockReturnValue(realUnsub);
+
+    const { initializePostHog, onFeatureFlagsLoaded } = await loadAnalytics();
+
+    const off = onFeatureFlagsLoaded(vi.fn());
+    initializePostHog();
+    off();
+
+    expect(realUnsub).toHaveBeenCalledTimes(1);
+  });
+
+  it("routes post-init subscribers directly to PostHog", async () => {
+    const realUnsub = vi.fn();
+    mockPosthog.onFeatureFlags.mockReturnValue(realUnsub);
+
+    const { initializePostHog, onFeatureFlagsLoaded } = await loadAnalytics();
+    initializePostHog();
+
+    const cb = vi.fn();
+    const off = onFeatureFlagsLoaded(cb);
+
+    expect(mockPosthog.onFeatureFlags).toHaveBeenCalledWith(cb);
+
+    off();
+    expect(realUnsub).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe("initializePostHog", () => {
+  it("is idempotent across repeat calls", async () => {
+    const { initializePostHog } = await loadAnalytics();
+
+    initializePostHog();
+    initializePostHog();
+
+    expect(mockPosthog.init).toHaveBeenCalledTimes(1);
+  });
+
+  it("does nothing when no API key is set", async () => {
+    vi.stubEnv("VITE_POSTHOG_API_KEY", "");
+    const { initializePostHog, onFeatureFlagsLoaded } = await loadAnalytics();
+
+    const cb = vi.fn();
+    onFeatureFlagsLoaded(cb);
+    initializePostHog();
+
+    expect(mockPosthog.init).not.toHaveBeenCalled();
+    expect(mockPosthog.onFeatureFlags).not.toHaveBeenCalled();
+  });
+});

apps/code/src/renderer/utils/analytics.ts

@@ -14,6 +14,14 @@ const log = logger.scope("analytics");
 
 let isInitialized = false;
 
+type PendingFlagListener = {
+  callback: () => void;
+  unsubscribe: (() => void) | null;
+};
+
+// Subscribers added before initializePostHog runs.
+const pendingFlagListeners = new Set<PendingFlagListener>();
+
 export function initializePostHog() {
   const apiKey = import.meta.env.VITE_POSTHOG_API_KEY;
   const apiHost =
@@ -44,6 +52,11 @@ export function initializePostHog() {
   posthog.register({ team: "posthog-code" });
 
   isInitialized = true;
+
+  for (const listener of pendingFlagListeners) {
+    listener.unsubscribe = posthog.onFeatureFlags(listener.callback);
+  }
+  pendingFlagListeners.clear();
 }
 
 /**
@@ -212,11 +225,19 @@ export function isFeatureFlagEnabled(flagKey: string): boolean {
  * Returns unsubscribe function.
  */
 export function onFeatureFlagsLoaded(callback: () => void): () => void {
-  if (!isInitialized) {
-    return () => {};
+  if (isInitialized) {
+    return posthog.onFeatureFlags(callback);
   }
 
-  return posthog.onFeatureFlags(callback);
+  const listener: PendingFlagListener = { callback, unsubscribe: null };
+  pendingFlagListeners.add(listener);
+  return () => {
+    if (listener.unsubscribe) {
+      listener.unsubscribe();
+    } else {
+      pendingFlagListeners.delete(listener);
+    }
+  };
 }
 
 /**