[plan] Update developer.instructions agent to emphasize safe-outputs-only write pattern #19542

Objective

Update the developer.instructions agent (.github/agents/developer.instructions.md) to more prominently document that the agent job must stay read-only, with all GitHub writes routed exclusively through the safe-outputs system.

Background

Discussion #19488 found that across 5 AI-generated workflows, one placed issues: write directly on the agent job — the only security deviation in all responses. The pattern is documented but not prominently enough for agents to consistently apply it.

Approach

1. Add a dedicated Security Posture section (or expand the existing one) in .github/agents/developer.instructions.md that makes the rule explicit:

   • Agent job permissions must be read-only for all scopes
   • All GitHub writes (issues, PRs, comments, discussions) must go through safe-outputs
   • Include a concrete ✅ / ❌ example showing the correct pattern vs. the anti-pattern

2. Example to add:

### ✅ Correct: Agent job read-only, writes via safe-outputs
permissions:
  contents: read
  pull-requests: read
  issues: read

safe_outputs:
  - create_issue
  - add_comment

### ❌ Incorrect: Write permissions on agent job
permissions:
  contents: read
  issues: write   # WRONG: agent job must stay read-only

3. Place this near the top of the security/permissions section so it appears early in the agent's context window.

Files to Modify

• .github/agents/developer.instructions.md — add/expand the safe-outputs-only write pattern section
• Run make recompile to regenerate any lock files if the agent file is used in compiled workflows

Acceptance Criteria

• The safe-outputs-only write pattern is documented with ✅ / ❌ examples
• The anti-pattern (write permissions on agent job) is explicitly called out
• The section appears prominently (not buried at the end)
• make recompile runs without errors

Generated by Plan Command for issue #discussion #19488 · ◷

• expires on Mar 6, 2026, 8:04 AM UTC