feat(cli): implement visual validation framework and TTY smoke tests

This change introduces a multi-layered validation strategy for the Gemini CLI UI, including:
- TTY Bootstrap Smoke Tests using node-pty to validate real terminal startup.
- Visual Regression Testing using SVG snapshots and AppRig.
- Core fixes for a scheduler hang and suppressed policy violations.
- Comprehensive documentation for maintainers.

packages/cli/integration-tests/bootstrap.test.ts

@@ -0,0 +1,37 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, beforeEach, afterEach } from 'vitest';
+import { TestRig } from '@google/gemini-cli-test-utils';
+
+describe('Gemini CLI TTY Bootstrap', () => {
+  let rig: TestRig;
+
+  beforeEach(() => {
+    rig = new TestRig();
+    rig.setup('TTY Bootstrap Smoke Test');
+  });
+
+  afterEach(async () => {
+    await rig.cleanup();
+  });
+
+  it('should render the interactive UI and display the ready marker in a TTY', async () => {
+    // Spawning the CLI in a pseudo-TTY with a dummy API key to bypass auth prompt
+    const run = await rig.runInteractive({
+      env: { GEMINI_API_KEY: 'dummy-key' },
+    });
+
+    // The ready marker we expect to see
+    const readyMarker = 'Type your message or @path/to/file';
+
+    // Verify the initial render completes and displays the marker
+    await run.expectText(readyMarker, 30000);
+
+    // If we reached here, the smoke test passed
+    await run.kill();
+  });
+});