feat(tests): add comprehensive happy path tests for session lifecycle

- Implemented session cleanup tests to ensure proper handling of session completions and cleanup operations.
- Added session initialization tests to verify session creation and observation queuing on first tool use.
- Created session summary tests to validate summary generation from conversation context upon session pause or stop.
- Developed integration tests to cover the full observation lifecycle, including context injection, observation queuing, and error recovery.
- Introduced reusable mock factories and scenarios for consistent testing across different test files.

tests/helpers/mocks.ts

@@ -0,0 +1,82 @@
+/**
+ * Reusable mock factories for testing dependencies.
+ */
+import { vi } from 'vitest';
+
+/**
+ * Mock fetch that succeeds with a JSON response
+ */
+export const mockFetchSuccess = (data: any = { success: true }) => {
+  return vi.fn().mockResolvedValue({
+    ok: true,
+    status: 200,
+    json: async () => data,
+    text: async () => JSON.stringify(data)
+  });
+};
+
+/**
+ * Mock fetch that fails with worker down error
+ */
+export const mockFetchWorkerDown = () => {
+  return vi.fn().mockRejectedValue(
+    new Error('ECONNREFUSED')
+  );
+};
+
+/**
+ * Mock fetch that returns 500 error
+ */
+export const mockFetchServerError = () => {
+  return vi.fn().mockResolvedValue({
+    ok: false,
+    status: 500,
+    json: async () => ({ error: 'Internal Server Error' }),
+    text: async () => 'Internal Server Error'
+  });
+};
+
+/**
+ * Mock database operations
+ */
+export const mockDb = {
+  createSDKSession: vi.fn().mockReturnValue(1),
+  addObservation: vi.fn().mockReturnValue(1),
+  getObservationById: vi.fn(),
+  getObservations: vi.fn().mockReturnValue([]),
+  searchObservations: vi.fn().mockReturnValue([]),
+  markSessionCompleted: vi.fn(),
+  getSession: vi.fn(),
+  getSessions: vi.fn().mockReturnValue([]),
+};
+
+/**
+ * Mock SDK agent
+ */
+export const mockSdkAgent = {
+  startSession: vi.fn(),
+  stopSession: vi.fn(),
+  processObservation: vi.fn(),
+  generateSummary: vi.fn(),
+};
+
+/**
+ * Mock session manager
+ */
+export const mockSessionManager = {
+  queueObservation: vi.fn(),
+  queueSummarize: vi.fn(),
+  getSession: vi.fn(),
+  createSession: vi.fn(),
+  completeSession: vi.fn(),
+};
+
+/**
+ * Helper to reset all mocks
+ */
+export const resetAllMocks = () => {
+  vi.clearAllMocks();
+  Object.values(mockDb).forEach(mock => mock.mockClear());
+  Object.values(mockSdkAgent).forEach(mock => mock.mockClear());
+  Object.values(mockSessionManager).forEach(mock => mock.mockClear());
+};