feat(core): instrument file system tools for JIT context discovery (#22082)

packages/core/src/tools/write-file.test.ts

@@ -115,6 +115,14 @@ vi.mock('../telemetry/loggers.js', () => ({
   logFileOperation: vi.fn(),
 }));
 
+vi.mock('./jit-context.js', () => ({
+  discoverJitContext: vi.fn().mockResolvedValue(''),
+  appendJitContext: vi.fn().mockImplementation((content, context) => {
+    if (!context) return content;
+    return `${content}\n\n--- Newly Discovered Project Context ---\n${context}\n--- End Project Context ---`;
+  }),
+}));
+
 // --- END MOCKS ---
 
 describe('WriteFileTool', () => {
@@ -1065,4 +1073,42 @@ describe('WriteFileTool', () => {
       expect(result.fileExists).toBe(true);
     });
   });
+
+  describe('JIT context discovery', () => {
+    const abortSignal = new AbortController().signal;
+
+    it('should append JIT context to output when enabled and context is found', async () => {
+      const { discoverJitContext } = await import('./jit-context.js');
+      vi.mocked(discoverJitContext).mockResolvedValue('Use the useAuth hook.');
+
+      const filePath = path.join(rootDir, 'jit-write-test.txt');
+      const content = 'JIT test content.';
+      mockEnsureCorrectFileContent.mockResolvedValue(content);
+
+      const params = { file_path: filePath, content };
+      const invocation = tool.build(params);
+      const result = await invocation.execute(abortSignal);
+
+      expect(discoverJitContext).toHaveBeenCalled();
+      expect(result.llmContent).toContain('Newly Discovered Project Context');
+      expect(result.llmContent).toContain('Use the useAuth hook.');
+    });
+
+    it('should not append JIT context when disabled', async () => {
+      const { discoverJitContext } = await import('./jit-context.js');
+      vi.mocked(discoverJitContext).mockResolvedValue('');
+
+      const filePath = path.join(rootDir, 'jit-disabled-write-test.txt');
+      const content = 'No JIT content.';
+      mockEnsureCorrectFileContent.mockResolvedValue(content);
+
+      const params = { file_path: filePath, content };
+      const invocation = tool.build(params);
+      const result = await invocation.execute(abortSignal);
+
+      expect(result.llmContent).not.toContain(
+        'Newly Discovered Project Context',
+      );
+    });
+  });
 });