test(07-01): add failing tests for sessionChatSlice initial state

RED phase of TDD:
- Write tests for all 12 initial state fields
- Validates messagesByChannel, activeChannel, channelType
- Validates unread tracking: unreadCounts, lastReadAt
- Validates fetch state: fetchStatus, fetchError
- Validates send state: sendStatus, sendError
- Validates pagination: nextCursors
- Validates UI state: isWindowOpen, windowPosition

Tests fail as expected - slice doesn't exist yet.

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

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

@@ -0,0 +1,81 @@
+import sessionChatReducer from '../sessionChatSlice';
+
+describe('sessionChatSlice initial state', () => {
+  test('has empty messagesByChannel object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.messagesByChannel).toEqual({});
+  });
+
+  test('has null activeChannel', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.activeChannel).toBeNull();
+  });
+
+  test('has null channelType', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.channelType).toBeNull();
+  });
+
+  test('has empty unreadCounts object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.unreadCounts).toEqual({});
+  });
+
+  test('has empty lastReadAt object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.lastReadAt).toEqual({});
+  });
+
+  test('has empty fetchStatus object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.fetchStatus).toEqual({});
+  });
+
+  test('has empty fetchError object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.fetchError).toEqual({});
+  });
+
+  test('has idle sendStatus', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.sendStatus).toBe('idle');
+  });
+
+  test('has null sendError', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.sendError).toBeNull();
+  });
+
+  test('has empty nextCursors object', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.nextCursors).toEqual({});
+  });
+
+  test('has isWindowOpen set to false', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.isWindowOpen).toBe(false);
+  });
+
+  test('has null windowPosition', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state.windowPosition).toBeNull();
+  });
+
+  test('complete initial state structure matches design', () => {
+    const state = sessionChatReducer(undefined, { type: 'unknown' });
+    expect(state).toEqual({
+      messagesByChannel: {},
+      activeChannel: null,
+      channelType: null,
+      unreadCounts: {},
+      lastReadAt: {},
+      fetchStatus: {},
+      fetchError: {},
+      sendStatus: 'idle',
+      sendError: null,
+      nextCursors: {},
+      isWindowOpen: false,
+      windowPosition: null
+    });
+  });
+});