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

### 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.

ここで説明されている orchestrator と functional-testing subagent のフローから始め、同じワークフローを VS Code で実行した場合の動作と比較し、関連するバグ #3049 を確認します。Work Item ID だけを使用して Functional Tester を再現し、出力ファイルの書き込みを禁止する指示を受けなくなっていること、および必要なテスト結果ファイルを作成できることを確認します。

索引モデルが issue の本文から書いたものです。