## Summary
- add a scoped level_id to ExtensionData and expose it through
level_id()
- remove thread_id/turn_id parameters from extension contributor inputs
where the scoped ExtensionData already carries that identity
- move turn-scoped extension data onto TurnContext so token usage and
lifecycle contributors can share the same turn store
## Testing
- cargo check -p codex-extension-api -p codex-core --tests
- cargo test -p codex-extension-api
- cargo test -p codex-guardian
- cargo test -p codex-core --lib
record_token_usage_info_notifies_extension_contributors
- cargo test -p codex-core --lib
submission_loop_channel_close_emits_thread_stop_lifecycle
- cargo test -p codex-core --lib
submission_loop_channel_close_aborts_active_turn_before_thread_stop_lifecycle
- just fix -p codex-extension-api
- just fix -p codex-guardian
- just fix -p codex-core
- just fmt
## Note
- Attempted cargo test -p codex-core; it aborted in
agent::control::tests::spawn_agent_fork_last_n_turns_keeps_only_recent_turns
with the existing stack overflow before the full suite completed.
## Why
`codex-core` still owns a growing amount of product-specific behavior.
This PR starts the extraction path by introducing a small, typed
first-party extension seam: features can install the contribution
families they actually own, while the host keeps lifecycle and state
ownership instead of pushing a broad service locator into the API.
See the `examples/` for illustration
## Known limitations
* Tool contract definition will be shared with core
* Fragments must be extracted
* Missing some contributors
