fix(tui): detach foreground shell before steering

[nightt5879]

Summary

• request that a blocking foreground Bash wait move to /jobs before enqueueing a same-turn steer
• keep the current busy-Enter queue behavior intact while covering every path that actually steers, including explicit steer and queued-message promotion
• distinguish true foreground waits from detached jobs that intentionally remain Running

Fixes #4930

Why this still applies on current main

Since the report, bare Enter during a busy turn was changed to queue a follow-up. The ordering bug still exists when that follow-up is explicitly promoted into the active turn (or the user uses the explicit steer chord): the shared steer boundary sent the message without first releasing a foreground shell wait. Centralizing the detach request in steer_user_message preserves the newer queue contract and fixes every real steer entry point.

The App and Engine share the same ShellManager. Setting its foreground-background request before enqueueing the steer lets the Bash wait loop return; the turn loop can then consume the steer. If shell tracking cannot accept the request, the existing lossless fallback restores the draft/queue instead of sending out of order.

Verification

• cargo fmt --all -- --check
• cargo check -p codewhale-tui --bin codewhale-tui --locked
• focused UI steer tests: 2 passed
• foreground/background classification tests: 2 passed
• queued-message promotion test: 1 passed
• real foreground shell detach test: 1 passed
• TUI Clippy with -D warnings: passed after allowing four Rust 1.95 lint classes already present in untouched upstream code
• full TUI binary suite before the final classification-only boundary test: 9,216 passed, 4 ignored, 4 failed; the three parallel shared-state/timing failures all passed immediately in isolation, while the documented Windows Job Object baseline failure reproduced in isolation and its failing test/implementation are unchanged
• git diff --check

Self-review

Reviewed the hook, pause-state rollback, queue fallback, Ctrl+B, detached-job, and engine-consumption paths. Message-submit denial happens before detach, normal busy Enter still queues, shell-manager errors fail closed, existing Ctrl+B status text is preserved, and detached jobs with a shell_task_id no longer masquerade as foreground waits.

[nightt5879]

@codex review

Please review current head 171e97054. Focus on the ordering and failure-atomicity of requesting foreground Bash backgrounding before same-turn steer dispatch, the shared ShellManager boundary, hook/paused-state/queue fallback behavior, and whether shell_task_id.is_none() correctly distinguishes a foreground wait from an already detached Running job. Please flag any race that could leave a steer blocked or detach the wrong shell.

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