Some Copilot CLI base instructions issued to a subagent prevent it from writing output to a file

[CezaryKlus]

Describe the bug

• I created a set of agents forming an orchestrator pattern for the full Work Item implementation
• When orchestrator executes a subagent responsible for functional testing this subagent consistently reports that it either could not write a test result file or was instructed not to write output to a file
• In either orchestrator or functional tester there are absolutely no instructions to prevent writing output files
• Orchestrator invokes the functional testing subagent only with the Work Item ID (no other runSubagent additional instructions)
• In other subagents for phases like Implementation everything works perfectly fine

Sample response from functional testing subagent (GPT 5.3 Codex) "...but I could not write the required notes file due the active session constraint: “Do NOT write output to files.”"

Related bug report: #3049

Affected version

No response

Steps to reproduce the behavior

No response

Expected behavior

No response

Additional context

The same workflow works 100% fine when run via VS Code.

[phebing-slashwhy]

This Bug still exists and also renders my set of agents unusable in Copilot CLI.
My agents report that rules like

CRITICAL: Do NOT write output to files.
Return ALL findings directly in your response text — never write results to a file

prevent them from writing files.
/diagnose helped my to identify the system message which causes this:

...
</prohibited_actions>

**CRITICAL: Do NOT write output to files.**
- Return ALL findings directly in your response text — never write results to a file
- NEVER use /tmp, mktemp, or any temporary file path — these are not portable and cause permission failures in sandboxed environments
- Do NOT use output redirection (`>`, `>>`, `tee`) to save results to files
- Do NOT use `cat > /path` or heredocs to create output files
- Your ONLY output channel is your response text — this is a hard requirement, not a suggestion

<subagent_model_preferences> 
...

Why did you choose such a restrictive system message?
Is it possible to change this?

[copilot-cli-bot]

This appears to be resolved as of GitHub Copilot CLI v1.0.88. Please update to that release or a newer stable version. We're closing this as completed. If it still happens, please comment with your version and reproduction steps.