## Why
User input queued during a long-running code-mode `exec` or `wait` can remain pending until the call returns. Allow these calls to yield early so Codex can receive the new input while the cell continues running.
## What changed
- Add the `instant_interrupt` feature flag, disabled by default.
- Watch queued user input for each sampling request and pass a shared preemption signal to code-mode `exec` and `wait` calls, including calls received later in the same response.
- Yield running cell IDs without stopping the cells, allowing subsequent `wait` calls to collect their results.
## Testing
Add integration coverage for enabled and disabled behavior, repeated steering during `exec` and `wait`, input deferred during compaction, and later calls in the same response. Verify that direct tool results and queued user messages are preserved, and add a scenario snapshot showing continuation after a cell yields.
GitOrigin-RevId: e33466a980d98e113bfb6c6a45c59de0cc7b3c1d