/research can't write it's research report

### Describe the bug

After running `/research TOPIC` the agent failed to write the research report to a file and instead complained that the "create" tool is not available.

Last response is:

```
I completed the research, but I could not save the markdown file to
/home/developer/.copilot/session-state/9ea25370-4826-4fbe-9574-0fe0fbe00d77/research/using-github-copilot-cli-with-worktrees.md because the required create tool is not
available in this session, and the delegated research agent only had read-only tools.
```

This was the first time I've tried `/research`, but everything else looked fine. After the above message it gave me a brief summary and when I asked it to print the report instead of writing to a file, it also printed what looked like the full report. Of course I can't verify if that is the same content as it would have written to the file or if some context etc. was lost.

### Affected version

GitHub Copilot CLI 1.0.40.

### Steps to reproduce the behavior

1. Run `/research some topic`
2. Wait for it to finish
3. The agent should complain that it can't create the research report

### Expected behavior

The agent should write the research report to a file.

### Additional context

_No response_

Start by reproducing `/research some topic` with GitHub Copilot CLI 1.0.40 and follow the command's research and report-writing flow. Check why the agent and delegated research agent lack the required create tool. Done means `/research` writes the completed markdown report to the session-state research path instead of only printing it.

Scritto dal modello di indicizzazione a partire dal testo della issue.