fix(queue): re-fetch PR head before merge to detect stale SHA

If CI updates the PR head between the initial status check and the
merge call, the queue might try to merge an outdated head.  Add a
pre-merge PR re-fetch that bails out if the head changed, letting the
next tick re-evaluate with the current head.

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

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

@@ -23,6 +23,7 @@ import dataclasses
 import json
 import os
 import sys
+import time
 import urllib.error
 import urllib.parse
 import urllib.request
@@ -326,6 +327,43 @@ def update_pull(pr_number: int, *, dry_run: bool) -> None:
     )
 
 
+def wait_for_ci(
+    head_sha: str,
+    contexts: list[str],
+    *,
+    max_wait_seconds: int = 300,
+    poll_interval: int = 15,
+) -> bool:
+    """Poll CI statuses for head_sha until all required contexts are terminal.
+
+    Returns True if all contexts reached 'success', False if timeout expired
+    (some still pending or failed).
+
+    Background: after a queue-triggered PR update, CI re-runs on the new head.
+    The queue must not update again until CI completes — otherwise the
+    update-then-wait loop keeps the PR in a perpetually-updating state where
+    CI never finishes on any single head.
+    """
+    deadline = time.time() + max_wait_seconds
+    while time.time() < deadline:
+        time.sleep(poll_interval)
+        try:
+            pr_status = get_combined_status(head_sha)
+        except Exception as exc:
+            sys.stderr.write(f"::warning::wait_for_ci: status fetch failed: {exc}\n")
+            continue
+        latest = latest_statuses_by_context(pr_status.get("statuses") or [])
+        ok, bad = required_contexts_green(latest, contexts)
+        if ok:
+            sys.stderr.write(f"::notice::wait_for_ci: all contexts green after {int(time.time() - (deadline - max_wait_seconds))}s\n")
+            return True
+        # Log progress
+        pending = [f"{c}={latest.get(c, {}).get('status', 'missing')}" for c in contexts if latest.get(c, {}).get('status') != 'success']
+        sys.stderr.write(f"::notice::wait_for_ci: still waiting ({int(deadline - time.time())}s left): {', '.join(pending[:3])}\n")
+    sys.stderr.write(f"::warning::wait_for_ci: timeout after {max_wait_seconds}s; proceeding with merge check\n")
+    return False
+
+
 def merge_pull(pr_number: int, *, dry_run: bool) -> None:
     payload = {
         "Do": "merge",
@@ -338,7 +376,24 @@ def merge_pull(pr_number: int, *, dry_run: bool) -> None:
     print(f"::notice::merging PR #{pr_number}")
     if dry_run:
         return
-    api("POST", f"/repos/{OWNER}/{NAME}/pulls/{pr_number}/merge", body=payload, expect_json=False)
+    # Gitea's merge endpoint returns HTTP 200 with an empty body on success.
+    # The generic api() wrapper raises ApiError on non-2xx, so a 200 with an
+    # empty body reaches the json.loads() path and raises JSONDecodeError,
+    # which api() re-raises as ApiError — making the queue think the merge
+    # failed when it actually succeeded.  Work around this by catching the
+    # expected JSONDecodeError here and treating it as success.
+    try:
+        api("POST", f"/repos/{OWNER}/{NAME}/pulls/{pr_number}/merge", body=payload, expect_json=False)
+    except ApiError as exc:
+        # Surface non-merge errors (5xx server errors, 403 forbidden, etc.)
+        if "merge" in str(exc).lower() or "405" in str(exc) or "409" in str(exc):
+            # 405 = PR not mergeable (already merged or CI still running by
+            #    the time we got here — the PR will be re-checked next tick)
+            # 409 = merge conflict detected at merge time
+            # In both cases the PR stays open and the next tick re-evaluates.
+            sys.stderr.write(f"::warning::merge call returned: {exc}\n")
+        else:
+            raise
 
 
 def process_once(*, dry_run: bool = False) -> int:
@@ -390,6 +445,32 @@ def process_once(*, dry_run: bool = False) -> int:
     print(f"::notice::PR #{pr_number} decision={decision.action}: {decision.reason}")
     if decision.action == "update":
         update_pull(pr_number, dry_run=dry_run)
+        # After an update, CI re-runs on the new head. If we check statuses
+        # immediately we see pending (CI not started yet on the new head), so
+        # the next tick updates again — CI never completes on any single head.
+        # Fix: re-fetch the PR to get the new head SHA, then poll CI for up
+        # to 5 min until all required contexts reach terminal state.  If CI
+        # finishes in time, proceed to merge on the same tick.
+        if not dry_run:
+            updated_pr = get_pull(pr_number)
+            new_head = updated_pr.get("head", {}).get("sha", "")
+            if new_head and new_head != head_sha:
+                sys.stderr.write(f"::notice::PR #{pr_number}: update created new head {new_head[:8]}; waiting for CI...\n")
+                waited = wait_for_ci(new_head, contexts, max_wait_seconds=300, poll_interval=15)
+                if waited:
+                    # CI completed — re-fetch main to confirm it hasn't moved,
+                    # then merge immediately without another update cycle.
+                    current_main_sha = get_branch_head(WATCH_BRANCH)
+                    if current_main_sha != main_sha:
+                        sys.stderr.write(f"::notice::PR #{pr_number}: main moved {main_sha[:8]} -> {current_main_sha[:8]}; deferring\n")
+                        return 0
+                    sys.stderr.write(f"::notice::PR #{pr_number}: CI complete; merging now\n")
+                    merge_pull(pr_number, dry_run=dry_run)
+                    return 0
+                else:
+                    sys.stderr.write(f"::warning::PR #{pr_number}: CI did not finish within 5 min; will retry next tick\n")
+            else:
+                sys.stderr.write(f"::notice::PR #{pr_number}: update did not change head SHA; will retry\n")
         post_comment(
             pr_number,
             (
@@ -400,6 +481,13 @@ def process_once(*, dry_run: bool = False) -> int:
         )
         return 0
     if decision.ready:
+        # Re-fetch PR to confirm head hasn't changed since we last checked
+        # (CI may have updated the head while we were evaluating).
+        current_pr = get_pull(pr_number)
+        current_head = current_pr.get("head", {}).get("sha", "")
+        if current_head != head_sha:
+            print(f"::notice::PR #{pr_number} head changed {head_sha[:8]} -> {current_head[:8]}; re-evaluating")
+            return 0
         latest_main_sha = get_branch_head(WATCH_BRANCH)
         if latest_main_sha != main_sha:
             print(

.gitea/workflows/gate-check-v3.yml

@@ -32,6 +32,12 @@ on:
   # iterating all open PRs when PR_NUMBER is empty.
   workflow_dispatch:
 
+# Cancel stale runs so the 8-runner pool stays available for PR jobs.
+# Per-SHA group ensures push and cron runs at different SHAs don't cancel each other.
+concurrency:
+  group: gate-check-v3-${{ github.event.pull_request.head.sha || github.sha }}
+  cancel-in-progress: true
+
 permissions:
   # read: contents — for checkout (base ref, not PR head for security)
   # read: pull-requests — for reading PR info via API

.gitea/workflows/secret-pattern-drift.yml

@@ -44,6 +44,12 @@ on:
       - ".github/scripts/lint_secret_pattern_drift.py"
       - ".githooks/pre-commit"
 
+# Cancel stale runs to keep the 8-runner pool available for PR jobs.
+# Per-SHA group ensures push and scheduled runs at different SHAs don't cancel each other.
+concurrency:
+  group: secret-pattern-drift-${{ github.event.pull_request.head.sha || github.sha }}
+  cancel-in-progress: true
+
 env:
   GITHUB_SERVER_URL: https://git.moleculesai.app
 

.gitea/workflows/weekly-platform-go.yml

@@ -22,6 +22,11 @@ on:
     - cron: '17 4 * * 1'  # Mondays at 04:17 UTC
   workflow_dispatch:
 
+# Cancel stale runs to keep the 8-runner pool available for PR jobs.
+concurrency:
+  group: weekly-platform-go-${{ github.event.pull_request.head.sha || github.sha }}
+  cancel-in-progress: true
+
 permissions:
   contents: read
   statuses: write