[Bug] Session cleanup deletes concurrent session task output, causing Bash commands to fail with exit code 1

**Bug Description**
╭─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ ✻ Bug report drafted: One session's startup cleanup deletes another live session's task output, surfacing as every Bash command returning exit 1 │
│ │ - What happened: In a long-running session with several other Claude Code sessions open on the same machine, every Bash invocation began returning `Exit cod… │
│ 1 to review · 2 to send · 0 to dismiss · +1 more queued │
╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

**Environment Info**
- Platform: linux
- Terminal: ghostty
- Version: 2.1.263
- Feedback ID: b1a3a07d-ca22-4529-b2f3-b915c5051ca2

**Errors**
```json
[]
```

No source files or tests are identified in the report. Start by reproducing the failure with concurrent Claude Code sessions on Linux and trace session-start cleanup and task-output handling; done means one session cannot delete another live session's output and Bash commands no longer return exit code 1.

Written by the indexing model from the issue text.