docs(plan): サブエージェントの権限マージの修正計画を作成

[yohi]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Please provide a description of the issue, the changes you made to fix it, and why they work. It is expected that you understand why your changes work and if you do not understand why at least say as much so a maintainer knows how much to value the PR.

If you paste a large clearly AI generated description here your PR may be IGNORED or CLOSED!

How did you verify your code works?

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• No "Type of change" checkbox is checked. Please select at least one.
• "How did you verify your code works?" section is empty. Please explain how you tested.
• Not all checklist items are checked. Please confirm you have tested locally and have not included unrelated changes.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate PRs Found

Several related PRs exist that address subagent permission handling and merging:

1. fix(opencode): inherit MCP tool allow permissions in subagent sessions #30288 - fix(opencode): inherit MCP tool allow permissions in subagent sessions

   • Directly related to subagent permission inheritance

2. fix(session): merge per-call tool rules into session permission #30529 - fix(session): merge per-call tool rules into session permission

   • Addresses permission merging at the session level

3. fix(task): respect subagent explicit edit:allow over inherited parent edit:deny #29235 - fix(task): respect subagent explicit edit:allow over inherited parent edit:deny

   • Related to subagent permission override logic

4. fix(task): subagent explicit edit:allow overrides parent edit:deny #27654 - fix(task): subagent explicit edit:allow overrides parent edit:deny

   • Similar permission precedence issue for subagents

5. fix: render permission and question prompts from nested subagent session #13719 - fix: render permission and question prompts from nested subagent session

   • Addresses permission handling in nested subagent sessions

Since PR #30845 is a documentation/plan PR (not a fix or feature), you may want to verify if any of these existing PRs (especially #30288, #30529, #29235) already document or implement the subagent permission merge fixes you're planning.