Tighten Sub-Issue Closer add_comment target contract

[Copilot]

Sub-Issue Closer was still emitting add_comment safe outputs without a numeric target under target: "*", so the post-step safe_outputs job rejected every comment even though the agent run completed. This aligns the workflow prompt with the earlier fix pattern already applied to other affected workflows.

• Workflow prompt contract

  • Require every add_comment emitted by Sub-Issue Closer to include issue_number.
  • Explicitly forbid targetless add_comment items when target: "*" is configured.
  • Instruct the workflow to reuse the same parent issue number for both update_issue and the matching add_comment.

• Regression coverage

  • Add a focused workflow contract test for sub-issue-closer.md.
  • Lock in the same guardrails already covered for pr-sous-chef.md and contribution-check.md.

• Expected emitted shape

  {
    "type": "add_comment",
    "issue_number": 123,
    "body": "🎉 **Automatically closed by Sub-Issue Closer**\n\nAll sub-issues have been completed."
  }

[Copilot]

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