# Specification: Mock Provider Hardening

## Background
The current `mock_gemini_cli.py` provider only tests the "happy path". It always returns successfully parsed JSON-L responses, which masks potential error-handling bugs in `ai_client.py` and `AppController`. To properly verify the system's robustness, the mock must be capable of failing realistically.

## Objective
Extend `mock_gemini_cli.py` to support negative testing paths, controlled via an environment variable `MOCK_MODE`.

## Requirements
1. **MOCK_MODE parsing:** The mock script must read `os.environ.get("MOCK_MODE", "success")`.
2. **malformed_json:** If mode is `malformed_json`, the mock should print a truncated or syntactically invalid JSON string to `stdout` and exit.
3. **error_result:** If mode is `error_result`, the mock should print a valid JSON string but with `"status": "error"` and an error message payload.
4. **timeout:** If mode is `timeout`, the mock should `time.sleep(120)` to force the parent process to handle a subprocess timeout.
5. **Integration Tests:** New tests must be written to explicitly trigger these modes using `ApiHookClient` and verify that the GUI displays an error state rather than crashing.