[codex] steer busy text by default

[juanfradb]

Summary

• default busy plain-text messages to same-turn steering instead of enqueueing for later
• add display.busy_input_mode = "queue" as an opt-out for the previous queue behavior
• wire Codex app-server sessions to native turn/steer with the active expectedTurnId

Behavior

Plain text sent while a session is busy now uses the active turn when steering is available. Empty messages, media/file messages, unavailable sessions, failed steering, and explicit busy_input_mode = "queue" continue to use the existing busy queue fallback.

Related but not duplicate: #523 adds an opt-in busy action mode, #669 adds an explicit /steer command, and #707 handles pre-execution message collection while leaving in-flight continuation unchanged.

Validation

• go test ./config ./core ./agent/codex ./cmd/cc-connect

[chenhg5]

LGTM. Codex steer busy text by default，CI pass，测试覆盖。

[ternary-chen]

Thanks for the earlier work here. I opened #1652 as a Draft based on the current main after testing the same busy-input path with Feishu and the Codex app-server backend.

The draft keeps queue as the backward-compatible default and makes steer opt-in. It also adds a capability-based interface, expectedTurnId protection, fallback to the existing queue, queue-only handling for attachments, history/watermark persistence, CUJ and targeted race coverage, and safer /ps behavior.

This clearly overlaps #839. I am not treating #1652 as an automatic replacement — happy to align, split, or close it if the author or maintainers prefer reviving this PR.