---
phase: 07-chat-infrastructure
plan: 01
type: tdd
status: completed
completedAt: 2026-01-27
---

# Phase 7 Plan 1: Redux Slice & Core Reducers Summary

**Created sessionChatSlice with all reducers using TDD methodology**

## Accomplishments

- Created sessionChatSlice.js with complete initial state structure matching CHAT_REDUX_DESIGN.md
- Implemented 7 reducers using strict TDD approach (RED-GREEN-REFACTOR):
  - `addMessageFromWebSocket`: Message handling with deduplication and unread logic
  - `setActiveChannel`: Channel selection for viewing
  - `openChatWindow`: Opens window and resets unread count
  - `closeChatWindow`: Closes window without affecting unread counts
  - `markAsRead`: Explicitly marks channel as read with timestamp
  - `incrementUnreadCount`: Manual unread count increment
  - `setWindowPosition`: UI position persistence
- Comprehensive unit test suite with 40 tests and 100% reducer coverage
- Message deduplication logic validated (critical for WebSocket + REST scenario)
- Unread tracking system tested and working across multi-channel scenarios
- 3 integration tests validate complete message flows and multi-channel behavior
- Registered sessionChat slice in Redux store configuration

## Files Created/Modified

### Created Files
- `jam-ui/src/store/features/sessionChatSlice.js` - Redux slice with 7 reducers and helper function
- `jam-ui/src/store/features/__tests__/sessionChatSlice.test.js` - Comprehensive unit and integration tests (40 tests)

### Modified Files
- `jam-ui/src/store/store.js` - Added sessionChat reducer to store configuration

## Test Coverage

**40 total tests passing:**
- 13 tests for initial state structure
- 8 tests for addMessageFromWebSocket (including deduplication)
- 2 tests for setActiveChannel
- 3 tests for openChatWindow
- 2 tests for closeChatWindow
- 3 tests for markAsRead
- 3 tests for incrementUnreadCount
- 3 tests for setWindowPosition
- 3 integration tests for complete flows

## Decisions Made

### Channel Key Construction
Implemented `getChannelKey()` helper function to construct channel keys:
- Session messages: Use `sessionId` directly (not prefixed with 'session-')
- Lesson messages: Use `lessonSessionId` directly
- Global messages: Use 'global' string

This matches the design doc specification where channel keys are used directly as IDs rather than prefixed strings.

### Message Deduplication Strategy
Used `Array.some()` to check for existing message by `id` before insertion. This is efficient for typical chat message counts and prevents duplicate messages when the same message arrives via both WebSocket and REST API.

### Unread Count Logic
Unread count increments when:
- Window is closed (regardless of active channel)
- Window is open BUT viewing a different channel

This ensures users see unread counts for background channels while preventing increments for the currently visible channel.

### Timestamp Handling
All timestamps use `new Date().toISOString()` for consistency with server-side timestamps. This ensures proper sorting and display across time zones.

## Issues Encountered

None. TDD approach caught all issues early:
- Initial tests validated state structure
- Core reducer tests validated message handling and deduplication
- Integration tests validated multi-reducer interactions
- All tests passed on first GREEN phase implementation

## Commit History

Task 1 commits:
- `fd44d1255` - test(07-01): add failing tests for sessionChatSlice initial state
- `e98504eba` - feat(07-01): implement sessionChatSlice with initial state structure

Task 2 commits:
- `60a559e58` - test(07-01): add failing tests for core reducers with message deduplication
- `15a658a5d` - feat(07-01): implement core reducers with message deduplication logic

Task 3 commits:
- `96d7188a4` - test(07-01): add failing tests for unread tracking and integration flows
- `7bafb3c69` - feat(07-01): implement unread tracking reducers and complete slice

## Next Phase Readiness

**Ready for Plan 07-02 (Async Thunks & API Integration):**
- State structure complete and tested
- All reducers implemented and validated
- Integration tests prove multi-reducer coordination works
- Message deduplication strategy validated
- Unread tracking foundation ready for WebSocket integration

**Phase 7 Plan 2 will implement:**
- `fetchChatHistory` async thunk for REST API
- `sendChatMessage` async thunk for sending messages
- WebSocket message handler integration
- Loading/error state management via extraReducers
