fix(scheduler): reject draft merge mutations

CHANGELOG.md

@@ -162,6 +162,10 @@
 
 ## Proposed
 
+- Reject Draft pull requests again at both direct-merge and auto-merge
+  mutation functions. This defense-in-depth boundary prevents a stale caller
+  decision from reaching guarded GitHub mutations after PR lifecycle changes.
+
 - Skip target-repository old-head Actions inventory when review execution is
   centralized. Same-repository stale-run cleanup remains enabled; central
   review lifecycle is handled in the configured dispatch repository, avoiding

docs/doctoring/draft-merge-mutation-boundary.md

@@ -0,0 +1,33 @@
+# Draft merge mutation boundary
+
+Decision date: **2026-09-07**
+
+## Problem
+
+The scheduler normally excludes Draft pull requests during inspection. A PR can
+change lifecycle state after that decision, or another caller can invoke the
+mutation helper directly. Without a second guard, direct merge or auto-merge
+could proceed from stale Ready-state authority.
+
+## Decision
+
+`enable_auto_merge` and `merge_pr` each reject `isDraft` before actor
+validation, head-SHA processing, or any GitHub command. The upstream decision
+filter remains in place; this is a minimal defense-in-depth invariant at the
+irreversible boundary.
+
+## Failure scenes
+
+- A Ready PR becomes Draft after inspection: mutation is refused.
+- A direct helper call supplies a Draft PR: no GitHub command is executed.
+- A non-Draft PR follows the existing guarded expected-head flow unchanged.
+
+## Evidence and follow-up
+
+RED commit: `2d140a84203a0df0cb86cd6b6ab31fc37bbdbda2`.
+Fresh exact-head hosted checks and independent review remain required.
+
+## Reference
+
+GitHub. (2026). *Pull requests and draft pull requests*.
+https://docs.github.com/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests

docs/product-technical-gap-baseline.md

@@ -3416,3 +3416,16 @@ same name in another file can carry the opposite safety property.**
 - **Evidence:** RED commit
   `08a16caa4fdb0d0d86c44bb8cd7aed611beaab7b`; fresh exact-head hosted checks
   remain required before integration.
+
+
+### Draft merge mutation boundary
+
+- **Status:** Proposed
+- **Owner:** `ContextualWisdomLab/.github`
+- **Problem:** Scheduler decision code filtered Draft PRs, but the direct-merge
+  and auto-merge mutation functions did not revalidate lifecycle state.
+- **Action:** Reject Draft PRs at both mutation entrypoints before actor, SHA,
+  or GitHub mutation processing.
+- **Evidence:** RED commit
+  `2d140a84203a0df0cb86cd6b6ab31fc37bbdbda2`; fresh exact-head hosted checks
+  remain required before integration.

scripts/ci/pr_review_merge_scheduler_core.py

@@ -2640,6 +2640,8 @@ def run_head_guarded_merge(
 
 def enable_auto_merge(repo: str, pr: dict[str, Any], *, dry_run: bool) -> None:
     """Enable auto-merge for a PR at its current head using an allowed method."""
+    if pr.get("isDraft"):
+        raise RuntimeError("enable-auto-merge refused for draft PR")
     number = str(pr["number"])
     if dry_run:
         return
@@ -2650,6 +2652,8 @@ def enable_auto_merge(repo: str, pr: dict[str, Any], *, dry_run: bool) -> None:
 
 def merge_pr(repo: str, pr: dict[str, Any], *, dry_run: bool) -> None:
     """Merge a current-head-approved PR immediately with a head guard."""
+    if pr.get("isDraft"):
+        raise RuntimeError("direct-merge refused for draft PR")
     number = str(pr["number"])
     if dry_run:
         return

tests/test_pr_review_merge_scheduler.py

@@ -10887,3 +10887,18 @@ def test_central_dispatch_skips_non_authoritative_target_actions_inventory(
     decision = inspect(make_pr(baseRefName="feature-base"), trigger_reviews=False)
 
     assert decision.action == "skip"
+
+
+def test_draft_pr_cannot_reach_merge_mutations(monkeypatch):
+    """Defense in depth rejects drafts at both guarded merge boundaries."""
+    calls = []
+    monkeypatch.setattr(sched, "run", lambda args: calls.append(args) or "")
+    monkeypatch.setenv("GITHUB_ACTIONS", "true")
+    monkeypatch.setenv("GH_TOKEN", "workflow-token")
+    draft_pr = make_pr(isDraft=True, headRefOid="a" * 40)
+
+    for mutation in (sched.enable_auto_merge, sched.merge_pr):
+        with pytest.raises(RuntimeError, match="draft PR"):
+            mutation("owner/repo", draft_pr, dry_run=False)
+
+    assert calls == []