---
phase: 15-real-time-synchronization
plan: 01
status: complete
started: 2026-02-06
completed: 2026-02-06
duration: ~45 min (including bug fixes from UAT)
commits:
  - 86206e199: "feat(15): verify WebSocket handler and clean debug logs"
  - e9dd992e2: "test(15): create real-time sync integration tests"
  - bfee9acdf: "fix(15): resolve UAT issues - uploader message visibility and chat history"
  - da4e864ab: "fix(15): correct API response field name (chats not messages)"
  - 5df60ad6c: "fix(15): pass sessionId to fetchChatHistory for session messages"
  - fce74152f: "fix(15): prevent infinite loop in chat history fetch"
  - e24c65590: "fix(15): use correct parameter name for chat API (music_session)"
---

# Plan 15-01 Summary: Real-time Sync Verification

## Objective

Verify and test real-time attachment synchronization across session participants.

## Completed Tasks

### Task 1: Verify WebSocket Handler Implementation ✓
- Verified handleChatMessage extracts all attachment fields correctly
- Cleaned up debug console.log statements from JKSessionScreen.js
- Confirmed sessionId is added from currentSession.id

### Task 2: Verify Deduplication Logic ✓
- Confirmed addMessageFromWebSocket uses `message.id` for deduplication
- Confirmed fetchChatHistory.fulfilled also deduplicates by id
- Both paths (WebSocket + REST API) use consistent deduplication

### Task 3: Create Real-time Sync Integration Tests ✓
- Created `test/attachments/real-time-sync.spec.ts` (215 lines)
- Tests cover: WebSocket message receipt, deduplication, chat history integration
- Uses Redux dispatch to simulate WebSocket messages

### Task 4: Human Verification ✓
- Multi-user testing performed with two browsers
- Identified and fixed multiple bugs during UAT

## Bug Fixes During UAT

### Issue 1 & 2: Uploader doesn't see their own attachment
**Root cause:** Backend's `server_publish_to_session` excludes sender via `exclude_client_id`
**Fix:** Added optimistic message in `uploadAttachment.fulfilled` for the uploader

### Issue 3: No messages after page reload
**Root cause:** `fetchChatHistory` was imported but never called
**Fix:** Added useEffect in JKChatMessageList to dispatch fetchChatHistory

### Issue 4: TypeError on chat window open
**Root cause:** API returns `{ chats: [...] }` but code expected `{ messages: [...] }`
**Fix:** Changed to extract `chats` field from API response

### Issue 5: Infinite loop when fetching chat
**Root cause:** Condition allowed retry on 'failed' status
**Fix:** Changed to only fetch when status is 'idle'

### Issue 6: "Failed to load message history"
**Root cause:** Backend expects `music_session` param, we sent `session_id`
**Fix:** Changed getChatMessages to use `music_session` parameter

## Known Limitation

**WebSocket only broadcasts to musicians:**
- Backend's `server_publish_to_session` uses `as_musician: true` filter
- Users without audio tracks (listeners/fans) don't receive real-time messages
- Workaround: Messages visible after page refresh via REST API
- This is a pre-existing backend limitation, not introduced by our changes
- Fix would require backend change (out of scope for v1.2)

## Files Modified

- `jam-ui/src/components/client/JKSessionScreen.js` - Cleaned debug logs, added user info to upload
- `jam-ui/src/components/client/chat/JKChatMessageList.js` - Added fetchChatHistory dispatch
- `jam-ui/src/store/features/sessionChatSlice.js` - Fixed API field name, added optimistic upload message
- `jam-ui/src/helpers/rest.js` - Fixed API parameter name (music_session)
- `jam-ui/src/store/features/__tests__/sessionChatSlice.test.js` - Updated test payloads
- `jam-ui/test/attachments/real-time-sync.spec.ts` - New integration tests

## Verification Results

| Test | Result |
|------|--------|
| Uploader sees own attachment | ✓ Pass (via optimistic update) |
| Other participants see attachment in real-time | ✓ Pass (for musicians) |
| No duplicate messages | ✓ Pass |
| Messages persist after page refresh | ✓ Pass |
| Attachments in chat history on join | ✓ Pass |

## Phase 15 Success Criteria

- [x] WebSocket handler verified and debug logs cleaned
- [x] Deduplication logic verified for both message paths
- [x] Integration tests created and checked in
- [x] Human verification confirms multi-user real-time sync works
- [x] No duplicate messages for any user
- [x] Attachments persist in chat history

## Next Steps

Phase 16: Attachment Finalization
- Error handling and edge case validation
- UAT and final integration testing
