## Why
An execution environment marked `starting` is not yet usable, but unrelated work can continue while it becomes ready.
## What changed
- Add developer guidance that explains execution-environment isolation and the resources that become available after startup.
- Tell the model to wait only when the current task needs the starting environment.
- Retain the guidance across world-state updates without duplicating it in request history.
## Testing
- Cover world-state transitions, history retention, rollback handling, and deferred-environment request deduplication.
GitOrigin-RevId: f12f9204d4cbddce50a70eb0998beb6b66cd2fa9
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