## Summary
- submit `Enter` steers immediately while a turn is already running
instead of routing them through `queued_user_messages`
- keep those submitted steers visible in the footer as `pending_steers`
until core records them as a user message or aborts the turn
- reconcile pending steers on `ItemCompleted(UserMessage)`, not
`RawResponseItem`
- emit user-message item lifecycle for leftover pending input at task
finish, then remove the TUI `TurnComplete` fallback
- keep `queued_user_messages` for actual queued drafts, rendered below
pending steers
## Problem
While the assistant was generating, pressing `Enter` could send the
input into `queued_user_messages`. That queue only drains after the turn
ends, so ordinary steers behaved like queued drafts instead of landing
at the next core sampling boundary.
The first version of this fix also used `RawResponseItem` to decide when
a steer had landed. Review feedback was that this is the wrong
abstraction for client behavior.
There was also a late edge case in core: if pending steer input was
accepted after the final sampling decision but before `TurnComplete`,
core would record that user message into history at task finish without
emitting `ItemStarted(UserMessage)` / `ItemCompleted(UserMessage)`. TUI
had a fallback to paper over that gap locally.
## Approach
- `Enter` during an active turn now submits a normal `Op::UserTurn`
immediately
- TUI keeps a local pending-steer preview instead of rendering that user
message into history immediately
- when core records the steer as `ItemCompleted(UserMessage)`, TUI
matches and removes the corresponding pending preview, then renders the
committed user message
- core now emits the same user-message lifecycle when
`on_task_finished(...)` drains leftover pending user input, before
`TurnComplete`
- with that lifecycle gap closed in core, TUI no longer needs to flush
pending steers into history on `TurnComplete`
- if the turn is interrupted, pending steers and queued drafts are both
restored into the composer, with pending steers first
## Notes
- `Tab` still uses the real queued-message path
- `queued_user_messages` and `pending_steers` are separate state with
separate semantics
- the pending-steer matching key is built directly from `UserInput`
- this removes the new TUI dependency on `RawResponseItem`
## Validation
- `just fmt`
- `cargo test -p codex-core
task_finish_emits_turn_item_lifecycle_for_leftover_pending_user_input --
--nocapture`
- `cargo test -p codex-tui`
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