test(07-01): add failing tests for core reducers with message deduplication

RED phase of TDD for Task 2:
- Write tests for addMessageFromWebSocket with comprehensive scenarios:
  * Add message to new/existing channel
  * Message deduplication by msg_id (critical for WebSocket + REST)
  * Sort messages by createdAt ascending
  * Unread count increment logic (window closed OR different channel)
  * Global vs session channel handling
- Write tests for setActiveChannel (channel + channelType)
- Write tests for openChatWindow (resets unread, updates lastReadAt)
- Write tests for closeChatWindow (preserves unread counts)

Tests fail as expected - action creators don't exist yet.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/store/features/__tests__/sessionChatSlice.test.js

@@ -1,4 +1,9 @@
-import sessionChatReducer from '../sessionChatSlice';
+import sessionChatReducer, {
+  addMessageFromWebSocket,
+  setActiveChannel,
+  openChatWindow,
+  closeChatWindow
+} from '../sessionChatSlice';
 
 describe('sessionChatSlice initial state', () => {
   test('has empty messagesByChannel object', () => {
@@ -79,3 +84,295 @@ describe('sessionChatSlice initial state', () => {
     });
   });
 });
+
+describe('addMessageFromWebSocket', () => {
+  test('adds message to new channel', () => {
+    const state = {
+      messagesByChannel: {},
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: null
+    };
+    const message = {
+      id: 'msg-1',
+      senderId: 'user-1',
+      senderName: 'Alice',
+      message: 'Hello',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.messagesByChannel['session-abc']).toBeDefined();
+    expect(newState.messagesByChannel['session-abc']).toHaveLength(1);
+    expect(newState.messagesByChannel['session-abc'][0]).toEqual(message);
+  });
+
+  test('adds message to existing channel', () => {
+    const existingMessage = {
+      id: 'msg-1',
+      message: 'Hello',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const state = {
+      messagesByChannel: {
+        'session-abc': [existingMessage]
+      },
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: null
+    };
+    const newMessage = {
+      id: 'msg-2',
+      senderId: 'user-2',
+      senderName: 'Bob',
+      message: 'Hi there',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:01:00Z'
+    };
+    const action = addMessageFromWebSocket(newMessage);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.messagesByChannel['session-abc']).toHaveLength(2);
+    expect(newState.messagesByChannel['session-abc'][1]).toEqual(newMessage);
+  });
+
+  test('deduplicates messages by msg_id', () => {
+    const message = {
+      id: 'msg-1',
+      senderId: 'user-1',
+      message: 'Hello',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const state = {
+      messagesByChannel: {
+        'session-abc': [message]
+      },
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: null
+    };
+    // Try to add same message again
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.messagesByChannel['session-abc']).toHaveLength(1);
+  });
+
+  test('sorts messages by createdAt ascending', () => {
+    const state = {
+      messagesByChannel: {
+        'session-abc': [
+          { id: 'msg-2', message: 'Second', createdAt: '2026-01-26T12:01:00Z' }
+        ]
+      },
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: null
+    };
+    const earlierMessage = {
+      id: 'msg-1',
+      senderId: 'user-1',
+      message: 'First',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(earlierMessage);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.messagesByChannel['session-abc']).toHaveLength(2);
+    expect(newState.messagesByChannel['session-abc'][0].id).toBe('msg-1');
+    expect(newState.messagesByChannel['session-abc'][1].id).toBe('msg-2');
+  });
+
+  test('increments unread count if window closed', () => {
+    const state = {
+      messagesByChannel: {},
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: 'session-abc'
+    };
+    const message = {
+      id: 'msg-1',
+      message: 'Hello',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.unreadCounts['session-abc']).toBe(1);
+  });
+
+  test('increments unread count if viewing different channel', () => {
+    const state = {
+      messagesByChannel: {},
+      unreadCounts: {},
+      isWindowOpen: true,
+      activeChannel: 'session-xyz'
+    };
+    const message = {
+      id: 'msg-1',
+      message: 'Hello',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.unreadCounts['session-abc']).toBe(1);
+  });
+
+  test('does not increment unread count if window open and viewing same channel', () => {
+    const state = {
+      messagesByChannel: {},
+      unreadCounts: {},
+      isWindowOpen: true,
+      activeChannel: 'session-abc'
+    };
+    const message = {
+      id: 'msg-1',
+      message: 'Hello',
+      channel: 'session',
+      sessionId: 'session-abc',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.unreadCounts['session-abc']).toBeUndefined();
+  });
+
+  test('handles global channel correctly', () => {
+    const state = {
+      messagesByChannel: {},
+      unreadCounts: {},
+      isWindowOpen: false,
+      activeChannel: null
+    };
+    const message = {
+      id: 'msg-1',
+      message: 'Hello world',
+      channel: 'global',
+      createdAt: '2026-01-26T12:00:00Z'
+    };
+    const action = addMessageFromWebSocket(message);
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.messagesByChannel['global']).toBeDefined();
+    expect(newState.messagesByChannel['global']).toHaveLength(1);
+  });
+});
+
+describe('setActiveChannel', () => {
+  test('sets active channel and type', () => {
+    const state = {
+      activeChannel: null,
+      channelType: null
+    };
+    const action = setActiveChannel({
+      channel: 'session-abc',
+      channelType: 'session'
+    });
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.activeChannel).toBe('session-abc');
+    expect(newState.channelType).toBe('session');
+  });
+
+  test('updates existing active channel', () => {
+    const state = {
+      activeChannel: 'session-abc',
+      channelType: 'session'
+    };
+    const action = setActiveChannel({
+      channel: 'global',
+      channelType: 'global'
+    });
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.activeChannel).toBe('global');
+    expect(newState.channelType).toBe('global');
+  });
+});
+
+describe('openChatWindow', () => {
+  test('opens window and resets unread count for active channel', () => {
+    const state = {
+      isWindowOpen: false,
+      activeChannel: 'session-abc',
+      unreadCounts: { 'session-abc': 5 },
+      lastReadAt: {}
+    };
+    const action = openChatWindow();
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.isWindowOpen).toBe(true);
+    expect(newState.unreadCounts['session-abc']).toBe(0);
+    expect(newState.lastReadAt['session-abc']).toBeTruthy();
+    // Verify it's an ISO timestamp
+    expect(newState.lastReadAt['session-abc']).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/);
+  });
+
+  test('opens window without active channel', () => {
+    const state = {
+      isWindowOpen: false,
+      activeChannel: null,
+      unreadCounts: {},
+      lastReadAt: {}
+    };
+    const action = openChatWindow();
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.isWindowOpen).toBe(true);
+    expect(Object.keys(newState.unreadCounts)).toHaveLength(0);
+  });
+
+  test('preserves other channel unread counts', () => {
+    const state = {
+      isWindowOpen: false,
+      activeChannel: 'session-abc',
+      unreadCounts: { 'session-abc': 5, 'global': 3 },
+      lastReadAt: {}
+    };
+    const action = openChatWindow();
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.unreadCounts['session-abc']).toBe(0);
+    expect(newState.unreadCounts['global']).toBe(3);
+  });
+});
+
+describe('closeChatWindow', () => {
+  test('closes window without changing unread counts', () => {
+    const state = {
+      isWindowOpen: true,
+      unreadCounts: { 'session-abc': 0, 'global': 2 }
+    };
+    const action = closeChatWindow();
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.isWindowOpen).toBe(false);
+    expect(newState.unreadCounts['session-abc']).toBe(0);
+    expect(newState.unreadCounts['global']).toBe(2);
+  });
+
+  test('closes already closed window', () => {
+    const state = {
+      isWindowOpen: false,
+      unreadCounts: {}
+    };
+    const action = closeChatWindow();
+    const newState = sessionChatReducer(state, action);
+
+    expect(newState.isWindowOpen).toBe(false);
+  });
+});