feat: add feature flag for AI Chat

.env.example

@@ -31,3 +31,6 @@ OPENAI_BASE_URL=xxx
 GOOGLE_CLIENT_ID=xxx
 GOOGLE_CLIENT_SECRET=xxx
 GOOGLE_HOSTED_DOMAIN=
+
+# The feature flags.
+FEATURE_AI_CHAT=true

src/routes/(main)/(protected)/+layout.server.ts

@@ -1,5 +1,6 @@
 import { error, redirect } from '@sveltejs/kit';
 
+import { env } from '$env/dynamic/private';
 import { db, type UserFindUniqueArgs, type UserGetPayload } from '$lib/server/db';
 
 import type { LayoutServerLoad } from './$types';
@@ -39,5 +40,8 @@ export const load: LayoutServerLoad = async (event) => {
     username: user.name,
     csrfToken: event.locals.session.csrfToken(),
     onboarded,
+    featureFlags: {
+      aiChat: env.FEATURE_AI_CHAT === 'true',
+    },
   };
 };

src/routes/(main)/(protected)/+layout.svelte

@@ -198,7 +198,9 @@
         />
       {/if}
 
-      <ChatWidget onclick={handleChatWidgetClick} />
+      {#if page.data.featureFlags.aiChat}
+        <ChatWidget onclick={handleChatWidgetClick} />
+      {/if}
     </div>
   </div>
 {/if}
@@ -327,6 +329,8 @@
   </Modal>
 {/if}
 
-<ChatView isopen={isChatViewOpen} onclose={handleChatViewClose} />
+{#if page.data.featureFlags.aiChat}
+  <ChatView isopen={isChatViewOpen} onclose={handleChatViewClose} />
+{/if}
 
 <OnboardingView isopen={isOnboardingViewOpen} onclose={handleOnboardingViewClose} />

src/routes/(main)/hooks.server.ts

@@ -1,6 +1,7 @@
-import { type Handle, redirect } from '@sveltejs/kit';
+import { type Handle, json, redirect } from '@sveltejs/kit';
 import { sequence } from '@sveltejs/kit/hooks';
 
+import { env } from '$env/dynamic/private';
 import { HOME_PATH, nanoid } from '$lib/helpers/index.js';
 import { learnerAuth } from '$lib/server/auth/index.js';
 import { logger } from '$lib/server/logger.js';
@@ -9,13 +10,25 @@ import { logger } from '$lib/server/logger.js';
  * A handle that adds a request ID to the response headers and attaches a scoped logger to the
  * event. Downstream handles are expected to use the scoped logger for logging.
  */
-const requestLoggingHandle: Handle = async ({ event, resolve }) => {
+const requestLoggingHandle: Handle = ({ event, resolve }) => {
   const requestId = nanoid();
 
   event.setHeaders({ 'X-Request-Id': requestId });
   event.locals.logger = logger.child({ requestId });
 
-  return await resolve(event);
+  return resolve(event);
+};
+
+/**
+ * A handle that gates API routes behind feature flags.
+ * Returns 403 for disabled features before any further processing.
+ */
+const featureFlagHandle: Handle = ({ event, resolve }) => {
+  if (event.url.pathname.startsWith('/api/messages') && env.FEATURE_AI_CHAT !== 'true') {
+    return json(null, { status: 403 });
+  }
+
+  return resolve(event);
 };
 
 /**
@@ -52,6 +65,7 @@ const routeProtectionHandle: Handle = async ({ event, resolve }) => {
 
 export const handle: Handle = sequence(
   requestLoggingHandle,
+  featureFlagHandle,
   learnerAuth.handle,
   routeProtectionHandle,
 );