fix: emit thread stop lifecycle on implicit shutdown

[jif-oai]

Why

The thread lifecycle contributor hooks from #22476 should observe every session teardown. The explicit Op::Shutdown path already emitted on_thread_stop, but when submission_loop exited because its submission channel closed, it only tore down runtime services. That meant extensions could miss the thread-stop lifecycle signal on implicit runtime shutdown.

What Changed

• Split shared runtime teardown into shutdown_runtime_services(...).
• Split thread-stop lifecycle emission into emit_thread_stop_lifecycle(...).
• Reused those helpers from both explicit shutdown and the channel-close shutdown path.
• Tracked whether Op::Shutdown was received so the explicit path does not double-emit lifecycle events after it exits the loop.
• Added a regression test that closes the submission channel and asserts ThreadLifecycleContributor::on_thread_stop runs once with the expected thread/session stores.

Testing

• cargo test -p codex-core submission_loop_channel_close_emits_thread_stop_lifecycle

[jif-oai]

@codex review

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[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 072fa9fbcf

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".