feat: phase 3 for git integration

tests/ipc/handlers.test.ts

@@ -144,6 +144,7 @@ const mockGitEngine = {
   checkAvailability: vi.fn(),
   getRepoState: vi.fn(),
   getStatus: vi.fn(),
+  getDiff: vi.fn(),
   initializeRepo: vi.fn(),
   ensureGitignore: vi.fn(),
   pruneLfsCache: vi.fn(),
@@ -318,6 +319,23 @@ describe('IPC Handlers', () => {
       });
     });
 
+    describe('git:diff', () => {
+      it('should pass project path and file path to GitEngine.getDiff', async () => {
+        mockGitEngine.getDiff.mockResolvedValue({
+          filePath: 'posts/first.md',
+          patch: 'diff --git a/posts/first.md b/posts/first.md',
+        });
+
+        const result = await invokeHandler('git:diff', '/repo', 'posts/first.md');
+
+        expect(mockGitEngine.getDiff).toHaveBeenCalledWith('/repo', 'posts/first.md');
+        expect(result).toEqual({
+          filePath: 'posts/first.md',
+          patch: 'diff --git a/posts/first.md b/posts/first.md',
+        });
+      });
+    });
+
     describe('git:init', () => {
       it('should pass project path to GitEngine.initializeRepo', async () => {
         mockGitEngine.initializeRepo.mockResolvedValue({ success: true });