#205 Apps: Implement testing framework and sandbox

## Parent Epic: #195 ## Description Create testing framework for app developers to test apps before deployment. ## Location engine/apps/testing/sandbox.py, engine/apps/testing/mock_context.py ## AppSandbox Class ### Constructor - app_class: App class to test - Creates isolated test environment ### test_action() Method ```python def test_action( action_name: str, config: dict | None = None, secrets: dict | None = None, **kwargs ) -> dict: ''' Returns: { 'result': <action result>, 'events': [<emitted events>], 'logs': [<log entries>], 'checkpoints': {<checkpoint data>}, 'http_requests': [<made requests>], } ''' ``` ### Features - Mock HTTP responses - Capture emitted events - Capture log entries - Capture checkpoints - Simulate replays (test idempotency) - Timeout testing ## MockAppContext Class ### Captured Data - events: list[dict] - logs: list[dict] - checkpoints: dict[str, Any] - http_requests: list[dict] - state: dict[str, Any] ### Mock HTTP ```python sandbox = AppSandbox(MyApp) sandbox.mock_http( url='https://api.example.com/*', response={'status': 200, 'json': {'ok': True}} ) ``` ### Simulate Replay ```python sandbox.set_checkpoint('step1', {'result': 'cached'}) result = sandbox.test_action('my_action', ...) # Verify checkpoint was returned, not re-executed ``` ## API Endpoint POST /api/v1/apps/{app_id}/test - Test app action in sandbox - Body: {action_name, config, secrets, kwargs, mock_http} - Permission: developer - Returns sandbox result ## Testing - Test sandbox isolation - Test mock HTTP - Test checkpoint replay - Test event capture - Test log capture