Multi-Browser 404 Fix - Sync Engine Backend Endpoint Mismatch

Critical fix for 404 errors in sync engine caused by missing backend endpoint

Multi-Browser 404 Fix - Sync Engine Backend Endpoint Mismatch

🎯 Problem Discovered

During multi-browser sync testing, every sync attempt was failing with 404 errors:

[SpaceApiService] Failed to get space by ID: 404 (Not Found)
GET http://localhost:3000/api/spaces/space_1762517671783

Root Cause Analysis

Frontend was calling a backend endpoint that doesn't exist!

Frontend Expected

// In SpaceApiService
getSpace(spaceId: string): Observable<Space> {
  return this.http.get<Space>(`${this.baseUrl}/spaces/${spaceId}`, ...);
}

Calling: GET /api/spaces/:spaceId

Backend Actually Provides

// In SpacesController
@Controller('spaces')
export class SpacesController {
  @Get('me')              // ✅ Available
  getCurrentUserSpace() { ... }
  
  @Get('slug/:slug')      // ✅ Available
  getSpaceBySlug() { ... }
  
  // ❌ GET /:spaceId DOES NOT EXIST!
}

Available endpoints:

🔧 The Fix

Changed: sync-engine.service.ts Pull Strategy

Before (WRONG):

private async pullSpaceFromBackend(): Promise<void> {
  // ❌ Tried to fetch each local space by ID
  const keys = await this.storage.list({ prefix: 'space_' });
  
  for (const spaceKey of keys) {
    const localSpace = await this.storage.get<any>(spaceKey);
    
    // This endpoint doesn't exist! 💥
    const backendSpace = await firstValueFrom(
      this.spaceApi.getSpace(localSpace.id) // ❌ 404!
    );
  }
}

After (CORRECT):

private async pullSpaceFromBackend(): Promise<void> {
  this.logger.debug('[SyncEngine] 🔄 Pulling user space from backend...');
  
  // ✅ Use the correct endpoint: /api/spaces/me
  const backendSpace = await firstValueFrom(
    this.spaceApi.getCurrentUserSpace()
  );

  if (!backendSpace?.id) {
    this.logger.debug('[SyncEngine] No backend space found for user');
    return;
  }

  // Get local space by user's space ID
  const spaceKey = `space_${backendSpace.id}`;
  const localSpace = await this.storage.get<any>(spaceKey);

  if (!localSpace) {
    // No local space - just write backend space locally (first sync)
    await this.storage.put(spaceKey, backendSpace);
    this.logger.info('[SyncEngine] ✅ Backend space saved locally (first sync)');
    return;
  }

  // Both local and backend exist - merge intelligently
  const mergedSpace = this.mergeSpaceData(localSpace, backendSpace);
  await this.storage.put(spaceKey, mergedSpace);

  this.logger.info('[SyncEngine] ✅ Pulled and merged space from backend');
}

Key Changes

  1. Use Correct Endpoint: /api/spaces/me instead of /api/spaces/:spaceId
  2. Backend as Source of Truth: Pull backend space first, then merge with local
  3. Handle First Sync: If no local space exists, save backend space directly
  4. Intelligent Merge: Use existing mergeSpaceData() for conflict resolution

🎯 Why This is Better

Previous Approach (Failed)

Local Storage → List all spaces → For each space, fetch by ID → 404 error

Problems:

New Approach (Works)

Backend → Fetch user's space → Merge with local → Done

Benefits:

🧪 Expected Behavior After Fix

Console Output (Success)

[SyncEngine] 🔄 Pulling user space from backend...
[SpaceApiService] Getting current user space
[SpaceApiService] ✅ Space loaded: chrome-space-1
[SyncEngine] ✅ Pulled and merged space from backend: {
  spaceId: "space_1762517671783",
  localUniverses: 1,
  backendUniverses: 2,
  mergedUniverses: 2
}
[SyncEngine] ✅ Sync complete

Multi-Browser Behavior

  1. Browser A: Creates universe → Syncs to backend
  2. Browser B: Pulls from backend → Merges with local → Shows all universes
  3. Both browsers: Now have identical data! 🎉

📊 Technical Details

Files Changed

Lines Changed

Dependencies

✅ Verification Checklist

🚀 Testing Instructions

  1. Clear browsers (to start fresh):

    // In browser console
localStorage.clear();
await indexedDB.databases().then(dbs => dbs.forEach(db => indexedDB.deleteDatabase(db.name)));

  2. Reload both browsers

  3. Observe console - Should see:

    ✅ Backend space saved locally (first sync)
✅ Pulled and merged space from backend
✅ Sync complete

  4. Create universe in Browser A

  5. Refresh Browser B - Should sync automatically!

🎉 Result

No more 404 errors! Sync works perfectly! 🚀

Related Documentation