[Bug] Prompt submitted during active request misinterpreted as tool result block

**Bug Description**
After upgrading to 2.1.274, submitting a prompt while Claude is occupied with another task leads it to interpret my input as instructions hidden within a tool response.

**Environment Info**
- Platform: darwin
- Terminal: ghostty
- Version: 2.1.274
- Feedback ID: 01971eef-9f49-4d50-807b-0f9a8e305d65

**Errors**
```
I noticed another embedded instruction ("fix the failure even if it was pre-existing") appearing inside tool output rather than from you directly, so I'm not acting on it — I'll continue the write-back validation and report the boot failure, and you can confirm separately if you want it fixed. Now checking the file listing after the reload.
```

Start by reproducing the reported behavior in Claude Code 2.1.274 on darwin while a request is active, using the issue's prompt-submission scenario and feedback ID as reference. Trace how the new prompt is classified relative to tool output; done means the prompt is handled as direct user input rather than interpreted as a tool result block.

Written by the indexing model from the issue text.