## Why
Deferred environments can become ready after a turn starts. Guardian approval
reviews must use the environment selected for the current step so their working
directory and permission context are not taken from the stale turn snapshot.
## What changed
- Carry `StepContext` through tool execution and approval handling.
- Add a Guardian review context that pairs the parent turn with the current
step's environment snapshot.
- Use that snapshot for Guardian prompts, reviewer sessions, and delegated
reviewer threads while retaining turn-level fallbacks for callers without a
step context.
## Testing
Added an integration test that makes a deferred remote environment ready before
an escalated command and verifies Guardian receives that environment's working
directory and denied-read policy instead of the initial local environment's.
GitOrigin-RevId: 779096bc7d0e0c7453a009c02141029714b9b407
dd43a9967f