test: add e2e tests for daemon auto-restart on rebuild

Verifies that:
- daemon restarts with the same port when daemon.js mtime is newer
- daemon does NOT restart when daemon.js has not changed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: piotrski

packages/e2e-tests/src/daemon-auto-restart.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import fs from 'node:fs';
+import path from 'node:path';
+import {
+  createTempStateDir,
+  getTestPort,
+  startDaemon,
+  waitForDaemon,
+  stopDaemon,
+  runCli,
+} from './helpers.js';
+import type { ChildProcess } from 'node:child_process';
+
+describe('Daemon auto-restart on rebuild', () => {
+  let stateDir: string;
+  let port: number;
+  let daemon: ChildProcess | null = null;
+
+  beforeEach(async () => {
+    stateDir = createTempStateDir();
+    port = getTestPort();
+    daemon = startDaemon(port, stateDir);
+    await waitForDaemon(stateDir);
+  });
+
+  afterEach(async () => {
+    await stopDaemon(daemon, stateDir);
+    daemon = null;
+  });
+
+  it('should restart daemon when startedAt is older than daemon.js', async () => {
+    const infoPath = path.join(stateDir, 'daemon.json');
+    const infoBefore = JSON.parse(fs.readFileSync(infoPath, 'utf-8'));
+    const pidBefore = infoBefore.pid;
+
+    // Simulate a daemon that was started long before the last build
+    // by backdating startedAt in daemon.json
+    infoBefore.startedAt = 1000;
+    fs.writeFileSync(infoPath, JSON.stringify(infoBefore, null, 2));
+
+    const result = await runCli(['get', 'tree'], stateDir);
+    expect(result.exitCode).toBe(0);
+
+    const infoAfter = JSON.parse(fs.readFileSync(infoPath, 'utf-8'));
+    expect(infoAfter.pid).not.toBe(pidBefore);
+    expect(infoAfter.port).toBe(port);
+
+    // Clean up the new daemon process
+    daemon = null;
+    try {
+      process.kill(infoAfter.pid, 'SIGTERM');
+    } catch {
+      // already dead
+    }
+  });
+
+  it('should not restart when daemon.js has not changed', async () => {
+    const infoPath = path.join(stateDir, 'daemon.json');
+    const infoBefore = JSON.parse(fs.readFileSync(infoPath, 'utf-8'));
+
+    const result = await runCli(['get', 'tree'], stateDir);
+    expect(result.exitCode).toBe(0);
+
+    const infoAfter = JSON.parse(fs.readFileSync(infoPath, 'utf-8'));
+    expect(infoAfter.pid).toBe(infoBefore.pid);
+  });
+});