security: remove VITE_TLSYNC_SECRET from frontend bundle

- Remove import.meta.env.VITE_TLSYNC_SECRET from syncService.ts
- Add optional token parameter to SyncConnectionOptions interface
  (caller passes token fetched from API, not a baked-in secret)
- Add clientEnvBlocklist in vite.config.ts to prevent sensitive VITE_
  env vars (TLSYNC_SECRET, MICROSOFT_CLIENT_SECRET*) from reaching bundle
- Remove VITE_TLSYNC_SECRET from .env.example
- Token auth for TLSync now handled server-side or via API endpoint

Ref: t_99d166c6

.env.example

@@ -27,7 +27,6 @@ VITE_SUPABASE_ANON_KEY=your-supabase-anon-key
 # TLSync (TLDraw Sync) Configuration
 # =============================================================================
 VITE_TLSYNC_URL=https://app.classroomcopilot.ai/tldraw
-VITE_TLSYNC_SECRET=your-tlsync-secret
 
 # =============================================================================
 # WhisperLive (Transcription) Configuration

src/services/tldraw/syncService.ts

@@ -15,6 +15,8 @@ export interface SyncConnectionOptions {
     color: string;
     roomId?: string;
     baseUrl: string;
+    /** Optional TLSync auth token (fetched from API server-side, never baked into bundle) */
+    token?: string;
 }
 
 export function createSyncConnectionOptions(options: SyncConnectionOptions) {
@@ -22,8 +24,8 @@ export function createSyncConnectionOptions(options: SyncConnectionOptions) {
         userId,
         displayName,
         roomId = 'multiplayer',
-        baseUrl
+        baseUrl,
-
+        token = ''
     } = options;
 
     // Ensure we have valid user info
@@ -72,7 +74,8 @@ export function createSyncConnectionOptions(options: SyncConnectionOptions) {
         roomId: effectiveRoomId
     });
 
-    const token = import.meta.env.VITE_TLSYNC_SECRET ?? ''
+    // Token is provided by the caller (e.g. fetched from API server-side).
+    // Never embed a shared secret in the frontend bundle.
     const tokenParam = token ? `?token=${encodeURIComponent(token)}` : ''
 
     return {

vite.config.ts

@@ -14,9 +14,16 @@ export default defineConfig(({ mode }) => {
 
   // Determine client-side env vars to expose
   const envPrefix = 'VITE_'
+  // Blocklist: sensitive env vars that must NEVER reach the client bundle.
+  const clientEnvBlocklist = new Set([
+    'VITE_TLSYNC_SECRET',
+    'VITE_MICROSOFT_CLIENT_SECRET',
+    'VITE_MICROSOFT_CLIENT_SECRET_ID',
+  ])
+
   const clientEnv = Object.fromEntries(
     Object.entries(env)
-      .filter(([key]) => key.startsWith(envPrefix))
+      .filter(([key]) => key.startsWith(envPrefix) && !clientEnvBlocklist.has(key))
       .map(([key, value]) => [`import.meta.env.${key}`, JSON.stringify(value)])
   )