fix: improve code-radiator fallback for large merges (ENOBUFS)

[Copilot]

The code-radiator workflow files a non-actionable issue when create_pull_request fails with ENOBUFS for large merges. Even with a proper two-parent merge commit, git format-patch --stdout is always run by the gh-aw safe-outputs infrastructure for policy enforcement — for 50+ commit merges this exceeds the 100MB buffer limit regardless of patch_format: bundle.

Changes

.github/workflows/code-radiator.md (prompt body only; no lock file recompilation needed)

• ENOBUFS warning: After the merge-commit verification step, add a note that large merges (50+ commits) can fail create_pull_request with ENOBUFS even when the merge commit has two parents. Directs the agent to the fallback step rather than retrying.

• Improved fallback issue body (step f):

  • Adds "patch too large" as an explicit failure reason
  • Instructs the agent to include the commit count (git rev-list --count origin/<target>..origin/main)
  • Adds a structured ### Details section for what was completed
  • Adds a ### Manual steps needed section with exact reproduction commands:

    git fetch origin
    git checkout -b <local-branch> origin/<target>
    git merge origin/main --no-edit -m "Merge branch 'main' into '<target>'"
    # Resolve any conflicts, then:
    git commit --no-edit
    git push origin <local-branch>
    gh pr create --base <target> --head <local-branch> \
      --title "🤖 Merge 'main' => '<target>'" \
      --body "Automated merge of \`main\` into \`<target>\`."