## Why
An inherited turn can suppress a fork's configured developer instructions, leaving the first side-chat request without its developer policy.
## What changed
- Move shared side-conversation instructions and the history boundary into `codex-context-fragments`.
- Inject the developer policy before the user-role boundary when creating a TUI side-chat fork, while retaining the configured instructions.
- Distinguish attached and temporary policies, applying the worktree restriction only to temporary side chats.
- Add guidance to set up recurring monitors in the main chat or a new chat because temporary side chats cannot run scheduled updates.
## Testing
Add a TUI integration test that checks the first side-chat model request contains the policy and boundary. Add a core request-history snapshot covering an attached side chat that preserves inherited context, policy, and its prior answer after resuming from disk.
GitOrigin-RevId: 889cb317dc3327457cd9ef0879ec9f77dbfaeeba