## What changed
- Carry `ShellEnvironmentPolicy` in each resolved `EnvironmentConfig` and use
the selected turn environment's policy for shell commands, user shell tasks,
and unified exec.
- Infer the policy from the thread configuration when an environment does not
provide its own resolved configuration.
- Redact the policy from `EnvironmentConfig` debug output because it can contain
explicit environment variable values.
## Testing
- Verify shell handlers and unified exec filter inherited variables according
to the selected environment while preserving its explicit overrides.
GitOrigin-RevId: 9f6a52aa4af60e5f17251a0e1b11e1926b779055