## Summary
- add experimental turn/start.environments params for per-turn
environment id + cwd selections
- pass selections through core protocol ops and resolve them with
EnvironmentManager before TurnContext creation
- treat omitted selections as default behavior, empty selections as no
environment, and non-empty selections as first environment/cwd as the
turn primary
## Testing
- ran `just fmt`
- ran `just write-app-server-schema`
- not run: unit tests for this stacked PR
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Co-authored-by: Codex <noreply@openai.com>