test(07-03): add failing tests for localStorage utilities

- Add 3 tests for saveLastReadAt (save, merge, error handling)
- Add 3 tests for loadLastReadAt (load, empty state, parse errors)
- Add 2 tests for clearLastReadAt (clear specific, clear all)
- All 8 tests failing (RED phase) - utilities not yet implemented

Part of Phase 7 Plan 3 (WebSocket Integration & Selectors)

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

jam-ui/src/helpers/__tests__/chatStorage.test.js

@@ -0,0 +1,132 @@
+/**
+ * Tests for localStorage utilities for chat lastReadAt persistence
+ * Tests save, load, and clear operations with error handling
+ */
+
+describe('chatStorage', () => {
+  let saveLastReadAt, loadLastReadAt, clearLastReadAt;
+
+  beforeAll(() => {
+    try {
+      const storage = require('../chatStorage');
+      saveLastReadAt = storage.saveLastReadAt;
+      loadLastReadAt = storage.loadLastReadAt;
+      clearLastReadAt = storage.clearLastReadAt;
+    } catch (e) {
+      // Module not yet created
+    }
+  });
+
+  beforeEach(() => {
+    localStorage.clear();
+  });
+
+  describe('saveLastReadAt', () => {
+    test('should fail - function not implemented yet', () => {
+      if (!saveLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      saveLastReadAt('session-abc', '2026-01-26T12:00:00Z');
+      const stored = localStorage.getItem('jk_chat_lastReadAt');
+      expect(stored).toBeTruthy();
+      const parsed = JSON.parse(stored);
+      expect(parsed['session-abc']).toBe('2026-01-26T12:00:00Z');
+    });
+
+    test('should fail - merge functionality not implemented yet', () => {
+      if (!saveLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      saveLastReadAt('session-abc', '2026-01-26T12:00:00Z');
+      saveLastReadAt('global', '2026-01-26T13:00:00Z');
+      const stored = localStorage.getItem('jk_chat_lastReadAt');
+      const parsed = JSON.parse(stored);
+      expect(parsed['session-abc']).toBe('2026-01-26T12:00:00Z');
+      expect(parsed['global']).toBe('2026-01-26T13:00:00Z');
+    });
+
+    test('should fail - error handling not implemented yet', () => {
+      if (!saveLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      // Mock localStorage.setItem to throw error
+      const originalSetItem = Storage.prototype.setItem;
+      Storage.prototype.setItem = jest.fn(() => {
+        throw new Error('QuotaExceededError');
+      });
+
+      expect(() => saveLastReadAt('session-abc', '2026-01-26T12:00:00Z')).not.toThrow();
+
+      Storage.prototype.setItem = originalSetItem;
+    });
+  });
+
+  describe('loadLastReadAt', () => {
+    test('should fail - function not implemented yet', () => {
+      if (!loadLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      localStorage.setItem('jk_chat_lastReadAt', JSON.stringify({
+        'session-abc': '2026-01-26T12:00:00Z',
+        'global': '2026-01-26T13:00:00Z'
+      }));
+      const data = loadLastReadAt();
+      expect(data['session-abc']).toBe('2026-01-26T12:00:00Z');
+      expect(data['global']).toBe('2026-01-26T13:00:00Z');
+    });
+
+    test('should fail - empty state not implemented yet', () => {
+      if (!loadLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      const data = loadLastReadAt();
+      expect(data).toEqual({});
+    });
+
+    test('should fail - parse error handling not implemented yet', () => {
+      if (!loadLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      localStorage.setItem('jk_chat_lastReadAt', 'invalid json');
+      const data = loadLastReadAt();
+      expect(data).toEqual({});
+    });
+  });
+
+  describe('clearLastReadAt', () => {
+    test('should fail - function not implemented yet', () => {
+      if (!clearLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      localStorage.setItem('jk_chat_lastReadAt', JSON.stringify({
+        'session-abc': '2026-01-26T12:00:00Z',
+        'global': '2026-01-26T13:00:00Z'
+      }));
+      clearLastReadAt('session-abc');
+      const stored = localStorage.getItem('jk_chat_lastReadAt');
+      const parsed = JSON.parse(stored);
+      expect(parsed['session-abc']).toBeUndefined();
+      expect(parsed['global']).toBe('2026-01-26T13:00:00Z');
+    });
+
+    test('should fail - clear all functionality not implemented yet', () => {
+      if (!clearLastReadAt) {
+        expect(true).toBe(false); // RED phase
+        return;
+      }
+      localStorage.setItem('jk_chat_lastReadAt', JSON.stringify({
+        'session-abc': '2026-01-26T12:00:00Z'
+      }));
+      clearLastReadAt();
+      const stored = localStorage.getItem('jk_chat_lastReadAt');
+      expect(stored).toBeNull();
+    });
+  });
+});