feat: add diagnostics tool for live command output monitoring

- Implemented diagnostics functionality to start, stop, and monitor background check commands.
- Created a DiagnosticsPanel for real-time output display in the UI.
- Added support for auto-detecting default diagnostics commands based on project configuration.
- Introduced run_checks tool to execute project verification commands and report results.
- Enhanced tools-extra with functions to parse AGENTS.md and package.json for check commands.
- Added diff review functionality to visualize changes made in the last turn.
- Implemented tests for diagnostics and run_checks functionalities to ensure reliability.

test/diff-review.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it } from 'bun:test';
+import { parseDiffHunks, renderDiffReview } from '../src/diff-review';
+
+const SAMPLE_DIFF = `diff --git a/src/foo.ts b/src/foo.ts
+@@ -1,5 +1,6 @@
+ import { a } from './a';
++import { b } from './b';
+ const x = 1;
+ const y = 2;
+ const z = 3;
+@@ -10,3 +11,2 @@
+ function foo() {
+-  return 0;
+ }
+diff --git a/src/bar.ts b/src/bar.ts
+@@ -1,4 +1,1 @@
+-a
+-b
+-c
++d
+`;
+
+describe('parseDiffHunks', () => {
+  it('finds hunk headers across files', () => {
+    const hunks = parseDiffHunks(SAMPLE_DIFF);
+    expect(hunks.length).toBe(3);
+    expect(hunks[0]!.file).toBe('src/foo.ts');
+    expect(hunks[0]!.oldStart).toBe(1);
+    expect(hunks[0]!.newStart).toBe(1);
+    expect(hunks[1]!.file).toBe('src/foo.ts');
+    expect(hunks[1]!.oldStart).toBe(10);
+    expect(hunks[1]!.newStart).toBe(11);
+    expect(hunks[2]!.file).toBe('src/bar.ts');
+    expect(hunks[2]!.oldStart).toBe(1);
+    expect(hunks[2]!.newStart).toBe(1);
+  });
+
+  it('captures hunk body including +/- lines', () => {
+    const hunks = parseDiffHunks(SAMPLE_DIFF);
+    expect(hunks[0]!.body).toContain('+import { b } from \'./b\';');
+    expect(hunks[0]!.body).toContain(' const x = 1;');
+    expect(hunks[1]!.body).toContain('-  return 0;');
+  });
+
+  it('returns empty array on empty diff', () => {
+    expect(parseDiffHunks('')).toEqual([]);
+  });
+
+  it('returns empty array when no hunk headers', () => {
+    expect(parseDiffHunks('diff --git a/x b/x\njust some text\n')).toEqual([]);
+  });
+});
+
+describe('renderDiffReview', () => {
+  it('renders with file:line anchors', () => {
+    const out = renderDiffReview(SAMPLE_DIFF);
+    expect(out).toContain('src/foo.ts:1');
+    expect(out).toContain('src/foo.ts:11');
+    expect(out).toContain('src/bar.ts:1');
+    expect(out).toContain('diff review:');
+  });
+
+  it('returns "no hunks to review" on empty diff', () => {
+    expect(renderDiffReview('')).toBe('no hunks to review');
+  });
+});