feat: add PR-only queue cleanup mode with per-PR dispatch gates (Closes #390)

Adds canonical pr-queue-cleanup workflow, report verifier, reviewer-only task
routing, and runbook guidance so operators can drain open PRs one canonical
review at a time with fail-closed boundaries on batching and unauthorized merges.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_llm_workflow_split.py

@@ -16,6 +16,7 @@ def test_all_workflow_files_exist():
         "reconcile-landed-pr.md",
         "create-issue.md",
         "work-issue.md",
+        "pr-queue-cleanup.md",
     ):
         assert (SKILL_DIR / "workflows" / name).is_file(), name
 
@@ -26,6 +27,7 @@ def test_skill_references_all_workflow_files():
         "workflows/reconcile-landed-pr.md",
         "workflows/create-issue.md",
         "workflows/work-issue.md",
+        "workflows/pr-queue-cleanup.md",
     ):
         assert name in SKILL
 
@@ -36,6 +38,7 @@ def test_skill_contains_mode_isolation_language():
     assert "reconcile-landed-pr" in SKILL
     assert "create-issue" in SKILL
     assert "work-issue" in SKILL
+    assert "pr-queue-cleanup" in SKILL
     assert "Do not mix modes" in SKILL or "do not mix modes" in SKILL.lower()
 
 
@@ -99,12 +102,24 @@ def test_work_issue_workflow_contract():
     assert "## 21. PR creation rules" in text
 
 
+def test_pr_queue_cleanup_workflow_contract():
+    text = (SKILL_DIR / "workflows" / "pr-queue-cleanup.md").read_text(
+        encoding="utf-8"
+    )
+    assert "canonical: true" in text
+    assert "exactly one" in text
+    assert "check_cleanup_task_allowed" in text
+    assert "resolve_cleanup_run_state" in text
+    assert "Next suggested PR" in text
+
+
 def test_final_report_schemas_exist():
     for name in (
         "review-merge-final-report.md",
         "reconcile-landed-final-report.md",
         "create-issue-final-report.md",
         "work-issue-final-report.md",
+        "pr-queue-cleanup-final-report.md",
     ):
         assert (SKILL_DIR / "schemas" / name).is_file(), name
 
@@ -124,6 +139,20 @@ def test_start_issue_template_references_work_issue_workflow():
     assert "workflows/work-issue.md" in text
 
 
+def test_pr_queue_cleanup_template_references_workflow():
+    text = (SKILL_DIR / "templates" / "pr-queue-cleanup.md").read_text(
+        encoding="utf-8"
+    )
+    assert "workflows/pr-queue-cleanup.md" in text
+    assert "pr_queue_cleanup" in text
+
+
+def test_pr_queue_cleanup_verifier_exported():
+    from review_proofs import assess_pr_queue_cleanup_report
+
+    assert callable(assess_pr_queue_cleanup_report)
+
+
 def test_reviewer_fallback_verifier_exported():
     from review_proofs import assess_reviewer_fallback_report
 
@@ -199,4 +228,23 @@ def test_mutation_categories_verifier_exported():
 def test_worktree_ownership_verifier_exported():
     from review_proofs import assess_worktree_ownership_report
 
-    assert callable(assess_worktree_ownership_report)
+    assert callable(assess_worktree_ownership_report)
+
+
+def test_pr_queue_cleanup_verifier_exported():
+    from review_proofs import assess_pr_queue_cleanup_report
+
+    assert callable(assess_pr_queue_cleanup_report)
+
+
+def test_pr_queue_cleanup_workflow_contract():
+    text = (SKILL_DIR / "workflows" / "pr-queue-cleanup.md").read_text(encoding="utf-8")
+    assert "canonical: true" in text
+    assert "task_mode: pr-queue-cleanup" in text
+    assert "## 1. Mode isolation" in text
+    assert "## 4. Terminal mutation chain" in text
+    assert "## 5. Fresh run per PR" in text
+    assert "exactly one" in text.lower()
+    assert "review-merge-pr.md" in text
+    assert "Next suggested PR" in text
+    assert "schemas/pr-queue-cleanup-final-report.md" in text