## Why
Failed environments were omitted from environment context, and `wait_for_environment` returned a generic failure or treated an already-failed environment as unselected. The model needs the failure reason to explain problems such as an empty repository.
## What changed
- Preserve the selected environment and error when startup or configuration fails.
- Include failed status and XML-escaped error details in environment context, and return the reason from `wait_for_environment` for failures detected before or during a wait.
- Limit error details to 256 bytes per environment and 512 bytes total in context, preserving UTF-8 boundaries. Limit wait failure details to 256 bytes.
## Testing
Add coverage for failures before a turn and while waiting, verifying that the model receives the reason and the turn completes. Add unit tests for XML escaping, incremental context updates, clearing errors on recovery, and UTF-8-safe truncation.
GitOrigin-RevId: 093ab9b447c7b3243fbb53b665180db95479f2a7
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