feat(web): add feature flag client with platform-service polling

web/src/app/providers.tsx

@@ -4,6 +4,7 @@ import { useEffect } from 'react';
 import { usePathname } from 'next/navigation';
 import { AuthProvider } from '@/lib/auth-context';
 import { initTelemetry, trackPageView } from '@/lib/telemetry';
+import { initFeatureFlags } from '@/lib/feature-flags';
 import type { ReactNode } from 'react';
 
 export function Providers({ children }: { children: ReactNode }) {
@@ -11,6 +12,7 @@ export function Providers({ children }: { children: ReactNode }) {
 
   useEffect(() => {
     initTelemetry();
+    initFeatureFlags({ platform: 'web' });
   }, []);
 
   useEffect(() => {

web/src/lib/feature-flags.ts

@@ -0,0 +1,70 @@
+/**
+ * Feature flag client — polls platform-service /flags/poll endpoint.
+ *
+ * Flags are fetched on init and cached in memory. Re-polls on a configurable
+ * interval (default 5 min). Consumers call `isEnabled('flag_key')`.
+ *
+ * Privacy: sends userId + platform only. No PII.
+ */
+
+import { PRODUCT_ID } from './auth-api';
+
+const PLATFORM_URL = process.env.NEXT_PUBLIC_PLATFORM_SERVICE_URL ?? 'https://api.chronomind.app';
+const POLL_INTERVAL_MS = 5 * 60 * 1000; // 5 minutes
+
+let _flags: Record<string, boolean> = {};
+let _initialized = false;
+let _intervalId: ReturnType<typeof setInterval> | null = null;
+
+interface PollParams {
+  userId?: string;
+  platform?: string;
+}
+
+async function fetchFlags(params: PollParams): Promise<Record<string, boolean>> {
+  try {
+    const qs = new URLSearchParams();
+    if (params.userId) qs.set('userId', params.userId);
+    if (params.platform) qs.set('platform', params.platform);
+    const res = await fetch(`${PLATFORM_URL}/api/flags/poll?${qs.toString()}`, {
+      headers: { 'x-product-id': PRODUCT_ID },
+    });
+    if (!res.ok) return _flags;
+    const data = await res.json();
+    return (data as { flags: Record<string, boolean> }).flags ?? {};
+  } catch {
+    return _flags;
+  }
+}
+
+/**
+ * Initialize the flag client. Call once on app startup.
+ * Fetches flags immediately and starts polling.
+ */
+export async function initFeatureFlags(params: PollParams = {}): Promise<void> {
+  if (_initialized) return;
+  _initialized = true;
+  const pollParams: PollParams = { platform: 'web', ...params };
+  _flags = await fetchFlags(pollParams);
+  _intervalId = setInterval(async () => {
+    _flags = await fetchFlags(pollParams);
+  }, POLL_INTERVAL_MS);
+}
+
+/** Check if a feature flag is enabled. Returns false if not found or not initialized. */
+export function isEnabled(key: string): boolean {
+  return _flags[key] === true;
+}
+
+/** Get all currently cached flags. */
+export function getAllFlags(): Readonly<Record<string, boolean>> {
+  return _flags;
+}
+
+/** Stop polling and reset state. Useful for tests. */
+export function resetFeatureFlags(): void {
+  if (_intervalId) clearInterval(_intervalId);
+  _intervalId = null;
+  _flags = {};
+  _initialized = false;
+}