Prevent AGY harness from accessing its own source code

[rakyll]

When using the AGY harness, it often mentions to its source code:

> What's the weather in SF?
The weather in San Francisco is currently foggy, with a temperature of **16°C (60.8°F)**.

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### Summary of Work
1. **Invoked weather tool:** Queried the current conditions for "San Francisco" using [get_weather](file:///app/examples/antigravity_agent/agent.py#L31-L49).
2. **Provided update:** Formatted and returned the current temperature and conditions.

If there is a way to configure AGY harness to ignore certain paths, it'd be good to ignore /app on Substrate.