Preserve late steer after turn finalization

[friel-openai]

Summary

• atomically detect user input accepted while a regular task is finalizing
• continue that task before exposing the thread as idle
• add a deterministic regression proving the steer is sampled exactly once and retains its client message ID

Related: #15842, #14054, #14404

Testing

• RUST_MIN_STACK=8388608 cargo test -p codex-core pending_input -- --nocapture
• cargo test -p codex-app-server turn_steer
• just fix -p codex-core
• just fmt

just argument-comment-lint -p codex-core is currently blocked because the repository pins nightly Rust 1.92 while SQLx 0.9 requires Rust 1.94. The changed call sites follow the argument-comment convention.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c5d74b9b3e

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".

[friel-openai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: 875de1ec11

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".

[itxaiohanglover]

Good fix with thorough test coverage! The PendingInputContinuationTask test scenario verifies that late steer input is preserved after turn finalization. The is_empty helper on TurnInputQueue is a clean addition.