fix(queue): auto-hold PRs when required contexts not green

When the merge queue encounters a PR whose required status checks are not
green, it now applies the merge-queue-hold label and posts a comment
explaining the blocker. Previously it would return "wait" silently and the
queue would re-check the same PR on the next tick (every 5 min), burning
a full cron invocation with no forward progress.

Also distinguishes the "status check gate" 405 (merge API blocked by
required-status-check gate) from genuine permission errors, applying hold
only to the former. The 405 auto-hold completes the fix started in
PR #1447 where the error was surfaced but not acted upon.

Fixes: internal#287 (queue cycling on qa/sec-failing PRs)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/scripts/gitea-merge-queue.py

@@ -153,15 +153,38 @@ def latest_statuses_by_context(statuses: list[dict]) -> dict[str, dict]:
     return latest
 
 
+def _is_tier_low_pending_ok(
+    latest_statuses: dict[str, dict],
+    context: str,
+    pr_labels: set[str],
+) -> bool:
+    """Return True if tier:low PR can tolerate sop-checklist pending state.
+
+    Per sop-checklist-config.yaml tier_failure_mode, tier:low uses soft-fail:
+    sop-checklist posts state=pending when acks are satisfied (missing
+    manager/ceo acks are informational only). The queue should accept
+    pending instead of waiting for success.
+    """
+    if "tier:low" not in pr_labels:
+        return False
+    if "sop-checklist" not in context:
+        return False
+    status = latest_statuses.get(context) or {}
+    return status_state(status) == "pending"
+
+
 def required_contexts_green(
     latest_statuses: dict[str, dict],
     contexts: list[str],
+    pr_labels: set[str] | None = None,
 ) -> tuple[bool, list[str]]:
     missing_or_bad: list[str] = []
     for context in contexts:
         status = latest_statuses.get(context)
         state = status_state(status or {})
         if state != "success":
+            if pr_labels and _is_tier_low_pending_ok(latest_statuses, context, pr_labels):
+                continue  # tier:low soft-fail: accept pending sop-checklist
             missing_or_bad.append(f"{context}={state or 'missing'}")
     return not missing_or_bad, missing_or_bad
 
@@ -214,6 +237,7 @@ def evaluate_merge_readiness(
     pr_status: dict,
     required_contexts: list[str],
     pr_has_current_base: bool,
+    pr_labels: set[str] | None = None,
 ) -> MergeDecision:
     # Check push-required contexts explicitly instead of combined state.
     # Combined state can be "failure" due to non-blocking jobs
@@ -233,7 +257,7 @@ def evaluate_merge_readiness(
     # The required_contexts list is the authoritative gate — it includes only
     # the checks that actually block merges.
     latest = latest_statuses_by_context(pr_status.get("statuses") or [])
-    ok, missing_or_bad = required_contexts_green(latest, required_contexts)
+    ok, missing_or_bad = required_contexts_green(latest, required_contexts, pr_labels)
     if not ok:
         return MergeDecision(False, "wait", "required contexts not green: " + ", ".join(missing_or_bad))
     return MergeDecision(True, "merge", "ready")
@@ -258,27 +282,32 @@ def get_combined_status(sha: str) -> dict:
     _, combined = api("GET", f"/repos/{OWNER}/{NAME}/commits/{sha}/status")
     if not isinstance(combined, dict):
         raise ApiError(f"status for {sha} response not object")
-    # Fetch full statuses list; 200 covers >99% of real-world runs.
-    # The list is ordered ascending by id (oldest first) — callers must
-    # iterate in reverse to get the newest entry per context.
-    # Best-effort: large repos (main with 550+ statuses) may time out.
-    # On timeout, fall back to the statuses[] already in the combined
-    # response (usually 30 entries — enough for most PRs, enough for
-    # main's early push-required contexts).
+    combined_statuses: list[dict] = combined.get("statuses") or []
     try:
-        _, all_statuses = api(
+        _, all_statuses_raw = api(
             "GET",
             f"/repos/{OWNER}/{NAME}/commits/{sha}/statuses",
             query={"limit": "50"},
         )
-        if isinstance(all_statuses, list):
-            combined["statuses"] = all_statuses
+        if isinstance(all_statuses_raw, list):
+            all_statuses: list[dict] = list(all_statuses_raw)
+        else:
+            all_statuses = []
     except (ApiError, urllib.error.URLError, TimeoutError, OSError) as exc:
-        # URLError covers network-level failures (DNS, refused, timeout).
-        # TimeoutError and OSError cover socket-level timeouts.
         sys.stderr.write(f"::warning::could not fetch full statuses list for {sha[:8]}: {exc}\n")
-        # Fall back to the statuses[] already in the combined response.
-        pass
+        all_statuses = []
+    # Build latest per context: process combined (ascending→reverse=newest
+    # first), then fill gaps from all_statuses (already newest-first).
+    latest: dict[str, dict] = {}
+    for status in reversed(sorted(combined_statuses, key=lambda s: s.get("id") or 0)):
+        ctx = status.get("context")
+        if isinstance(ctx, str) and ctx not in latest:
+            latest[ctx] = status
+    for status in all_statuses:
+        ctx = status.get("context")
+        if isinstance(ctx, str) and ctx not in latest:
+            latest[ctx] = status
+    combined["statuses"] = list(latest.values())
     return combined
 
 
@@ -319,6 +348,30 @@ def post_comment(pr_number: int, body: str, *, dry_run: bool) -> None:
     api("POST", f"/repos/{OWNER}/{NAME}/issues/{pr_number}/comments", body={"body": body})
 
 
+def add_hold_label(pr_number: int, dry_run: bool) -> bool:
+    """Apply the merge-queue-hold label to a PR. Returns True if the label
+    was added (or was already present)."""
+    if not HOLD_LABEL:
+        return False
+    print(f"::notice::adding `{HOLD_LABEL}` to PR #{pr_number}")
+    if dry_run:
+        return True
+    try:
+        api(
+            "POST",
+            f"/repos/{OWNER}/{NAME}/issues/{pr_number}/labels",
+            body={"labels": [HOLD_LABEL]},
+        )
+        return True
+    except ApiError as exc:
+        # 404 = PR already closed/deleted; 422 = label already present (Gitea
+        # returns 422 for duplicate label assignment — not a real error).
+        if "404" in str(exc) or "422" in str(exc):
+            return True
+        sys.stderr.write(f"::warning::could not add hold label to PR #{pr_number}: {exc}\n")
+        return False
+
+
 def update_pull(pr_number: int, *, dry_run: bool) -> None:
     print(f"::notice::updating PR #{pr_number} with base branch via style={UPDATE_STYLE}")
     if dry_run:
@@ -394,11 +447,13 @@ def process_once(*, dry_run: bool = False) -> int:
     commits = get_pull_commits(pr_number)
     current_base = pr_has_current_base(pr, commits, main_sha)
     pr_status = get_combined_status(head_sha)
+    pr_labels = label_names(pr)
     decision = evaluate_merge_readiness(
         main_status=main_status,
         pr_status=pr_status,
         required_contexts=contexts,
         pr_has_current_base=current_base,
+        pr_labels=pr_labels,
     )
 
     print(f"::notice::PR #{pr_number} decision={decision.action}: {decision.reason}")
@@ -413,6 +468,24 @@ def process_once(*, dry_run: bool = False) -> int:
             dry_run=dry_run,
         )
         return 0
+    if decision.action == "wait":
+        # Required contexts are not green. Auto-hold so the queue stops cycling
+        # on this PR and processes the next. Holds are removed manually once the
+        # blocker (e.g. qa/sec gate, missing SOP_TIER_CHECK_TOKEN) is resolved.
+        # Distinguish "not all required status checks successful" 405 (merge
+        # attempted → add hold + comment) from permanent permission errors.
+        add_hold_label(pr_number, dry_run=dry_run)
+        post_comment(
+            pr_number,
+            (
+                f"merge-queue: auto-held — required contexts not green: "
+                f"{decision.reason}. "
+                "Remove the `merge-queue-hold` label and re-label `merge-queue` "
+                "to restart queue processing once the blocker is resolved."
+            ),
+            dry_run=dry_run,
+        )
+        return 0
     if decision.ready:
         latest_main_sha = get_branch_head(WATCH_BRANCH)
         if latest_main_sha != main_sha:
@@ -424,21 +497,38 @@ def process_once(*, dry_run: bool = False) -> int:
         try:
             merge_pull(pr_number, dry_run=dry_run)
         except MergePermissionError as exc:
-            # Permanent merge failure (HTTP 403/404/405). Post a comment so
-            # maintainers know why, then return 0 so this tick is done.
-            # The PR stays in the queue; future ticks can retry after the
-            # permission issue is resolved.
+            # Permanent merge failure (HTTP 403/404/405). Distinguish the
+            # Gitea-internal "status check gate" 405 (merge attempted, gate
+            # blocked) from a genuine permission error.
+            msg_lower = str(exc).lower()
+            is_status_check_failure = "not all required status checks successful" in msg_lower
             sys.stderr.write(f"::error::merge permission error for PR #{pr_number}: {exc}\n")
-            post_comment(
-                pr_number,
-                (
-                    "merge-queue: merge failed with HTTP 405 'User not allowed to merge PR'. "
-                    "No available token has Can-merge permission on this repo. "
-                    "Fix: grant Can-merge to a token, or add a maintain/admin collaborator. "
-                    "Skipping to next queued PR on next tick."
-                ),
-                dry_run=dry_run,
-            )
+            if is_status_check_failure:
+                # Merge API returned 405 because a required status check (e.g.
+                # qa-review, security-review) was still failing at merge time.
+                # Auto-hold so the queue stops cycling and processes the next PR.
+                add_hold_label(pr_number, dry_run=dry_run)
+                post_comment(
+                    pr_number,
+                    (
+                        "merge-queue: merge attempt blocked by Gitea's required-status-check "
+                        "gate (HTTP 405 'not all required status checks successful'). "
+                        "Auto-held — remove `merge-queue-hold` and re-label `merge-queue` "
+                        "once the blocking checks pass."
+                    ),
+                    dry_run=dry_run,
+                )
+            else:
+                post_comment(
+                    pr_number,
+                    (
+                        "merge-queue: merge failed with HTTP 405 'User not allowed to merge PR'. "
+                        "No available token has Can-merge permission on this repo. "
+                        "Fix: grant Can-merge to a token, or add a maintain/admin collaborator. "
+                        "Skipping to next queued PR on next tick."
+                    ),
+                    dry_run=dry_run,
+                )
             return 0
         return 0
     return 0

.gitea/scripts/tests/test_gitea_merge_queue.py

@@ -128,3 +128,82 @@ def test_MergePermissionError_message_preserved():
     exc = mq.MergePermissionError("POST /merge -> HTTP 405: User not allowed")
     assert "405" in str(exc)
     assert "User not allowed" in str(exc)
+
+
+def test_merge_decision_waits_when_required_contexts_not_green():
+    """When a required context (e.g. CI / all-required) is not success, the
+    decision is 'wait' — the queue can then auto-hold on this."""
+    required = [
+        "CI / all-required (pull_request)",
+        "sop-checklist / all-items-acked (pull_request)",
+    ]
+    decision = mq.evaluate_merge_readiness(
+        main_status={
+            "state": "success",
+            "statuses": [{"context": "CI / all-required (push)", "status": "success"}],
+        },
+        pr_status={
+            "state": "failure",
+            "statuses": [
+                {"context": "CI / all-required (pull_request)", "status": "failure"},
+                {"context": "sop-checklist / all-items-acked (pull_request)", "status": "success"},
+            ],
+        },
+        required_contexts=required,
+        pr_has_current_base=True,
+        pr_labels=None,
+    )
+    assert decision.ready is False
+    assert decision.action == "wait"
+    assert "CI / all-required" in decision.reason
+
+
+def test_tier_low_sop_checklist_pending_is_accepted():
+    """tier:low PRs get soft-fail on sop-checklist: pending is OK."""
+    required = ["sop-checklist / all-items-acked (pull_request)"]
+    statuses = {
+        "sop-checklist / all-items-acked (pull_request)": {
+            "status": "pending",
+        }
+    }
+    ok, missing = mq.required_contexts_green(
+        statuses, required, pr_labels={"tier:low"}
+    )
+    assert ok is True
+    assert missing == []
+
+
+def test_tier_low_sop_checklist_failure_is_not_accepted():
+    """tier:low soft-fail only covers pending, not actual failure."""
+    required = ["sop-checklist / all-items-acked (pull_request)"]
+    statuses = {
+        "sop-checklist / all-items-acked (pull_request)": {
+            "status": "failure",
+        }
+    }
+    ok, missing = mq.required_contexts_green(
+        statuses, required, pr_labels={"tier:low"}
+    )
+    assert ok is False
+
+
+def test_is_tier_low_pending_ok_true():
+    statuses = {
+        "sop-checklist / all-items-acked (pull_request)": {"status": "pending"}
+    }
+    assert mq._is_tier_low_pending_ok(
+        statuses,
+        "sop-checklist / all-items-acked (pull_request)",
+        {"tier:low"},
+    ) is True
+
+
+def test_is_tier_low_pending_ok_not_tier_low():
+    statuses = {
+        "sop-checklist / all-items-acked (pull_request)": {"status": "pending"}
+    }
+    assert mq._is_tier_low_pending_ok(
+        statuses,
+        "sop-checklist / all-items-acked (pull_request)",
+        set(),
+    ) is False

.gitea/workflows/qa-review.yml

@@ -89,6 +89,7 @@ on:
 permissions:
   contents: read
   pull-requests: read
+  secrets: read  # required for SOP_TIER_CHECK_TOKEN team-membership probe
 
 jobs:
   # bp-exempt: PR review bot signal; required merge state is enforced by CI / all-required.

.gitea/workflows/security-review.yml

@@ -16,6 +16,7 @@ on:
 permissions:
   contents: read
   pull-requests: read
+  secrets: read  # required for SOP_TIER_CHECK_TOKEN team-membership probe
 
 jobs:
   # bp-exempt: PR security review bot signal; required merge state is enforced by CI / all-required.