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Architecture: Bug Fix: New Chat Removing Old Conversations

Date: 2026-01-29

Solution​

Fix 1: Intelligent Merge in Sync​

Changed syncConversationsFromMongoDB() to merge intelligently:

// NEW (FIXED) CODE:
// 1. Create maps for fast lookup
const existingMap = new Map(state.conversations.map((c) => [c.id, c]));

// 2. Merge: Update existing conversations, add new ones
mongoConversations.forEach((mongoConv) => {
  const existing = existingMap.get(mongoConv.id);
  if (existing) {
    // Keep local messages/events, update metadata from MongoDB
    merged.push({
      ...existing,
      title: mongoConv.title,
      updatedAt: mongoConv.updatedAt,
      // Keep existing messages and events!
    });
  } else {
    merged.push(mongoConv);
  }
});

// 3. Add any local-only conversations
state.conversations.forEach((localConv) => {
  if (!processedIds.has(localConv.id)) {
    merged.push(localConv);
  }
});

// 4. Sort by most recent first
merged.sort((a, b) => b.updatedAt.getTime() - a.updatedAt.getTime());

Benefits:

  • ✅ Preserves existing conversations
  • ✅ Keeps local messages and events
  • ✅ Adds new conversations from MongoDB
  • ✅ Maintains proper sort order
  • ✅ No data loss

Fix 2: Immediate Local Store Update​

Changed the new chat creation flow:

// NEW FLOW:
1. Create in MongoDB → GET ID
2. Add to local store IMMEDIATELY
3. Redirect to new conversation
// Sync happens later asynchronously
// Add to local store immediately
const newConversation = {
  id: conversation._id,
  title: conversation.title,
  createdAt: new Date(conversation.created_at),
  updatedAt: new Date(conversation.updated_at),
  messages: [],
  a2aEvents: [],
};

useChatStore.setState((state) => ({
  conversations: [newConversation, ...state.conversations],
  activeConversationId: conversation._id,
}));

Benefits:

  • ✅ Instant UI update
  • ✅ New conversation appears in sidebar immediately
  • ✅ Old conversations remain visible
  • ✅ No delay waiting for sync

Code Changes​

File: ui/src/store/chat-store.ts​

Changed: syncConversationsFromMongoDB() method

  • Lines 389-397 (old: naive replacement)
  • Lines 389-428 (new: intelligent merge)

Impact: Better merge logic preserves all conversations

File: ui/src/app/(app)/chat/page.tsx​

Changed: New conversation creation flow

  • Lines 27-42 (old: create + sync)
  • Lines 27-52 (new: create + immediate local update)

Impact: Instant UI update, no data loss

Edge Cases Handled​

  1. Race Conditions: Multiple rapid "New Chat" clicks
  2. Sync Timing: Conversation created during sync operation
  3. Local vs MongoDB: Conversations in different storage layers
  4. Order Preservation: Most recent conversations first
  5. Message Retention: Local messages preserved during sync

Performance Impact​

Before:

  • Sync operation: O(n) replacement
  • UI update: Delayed until sync completes
  • Risk: Data loss during sync

After:

  • Sync operation: O(n) merge (same complexity, better logic)
  • UI update: Immediate (better UX)
  • Risk: Zero data loss

Future Improvements​

Potential enhancements:

  1. Optimistic Updates: Show new conversation immediately, sync later
  2. Conflict Resolution: Handle concurrent edits across devices
  3. Incremental Sync: Only fetch new/updated conversations
  4. Local Draft Indicator: Show which conversations have unsaved changes
  5. Sync Queue: Queue operations during offline mode