[Bug] Tool results leaking between sessions in multi-session environments

**Bug Description**
Some tool calling results are leaking between sessions. Example: Session A updates file A. Session B sees Update(file A) and all the file edition diff. Seems to be a latent UI and background sessions leakage bug.

**Environment Info**
- Platform: linux
- Terminal: xterm-256color
- Version: 2.1.273
- Feedback ID: 0c6e2d1e-765d-4d68-a714-1ac70eb4ccad

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

Reproduce the issue in two concurrent sessions on Linux with version 2.1.273, where one session updates a file and the other observes the tool result and diff. Trace how tool-call results are associated with sessions; done means each session only displays its own results and file diffs, with no cross-session leakage.

Written by the indexing model from the issue text.