fix(webhook): re-read PR labels at review start so a late AI-USAGE counts

Labelling a PR is two webhook events. AI-REVIEW arrives first, the review
claims (repo, index, sha) and starts; the AI-USAGE event that follows a
moment later hits the in-flight dedupe and is dropped. `report_usage` was
snapshotted from the first payload, which had not seen AI-USAGE yet, so the
review posted without its usage block even though the label was on the PR by
the time it finished — observed on gitea_admin/pragent#9 (`usage=False` in
the pod log, no <details> section in the posted review).

Re-read the labels from the API at review start and upgrade the flag. The
read is best-effort: any failure logs and returns [], leaving the payload's
verdict intact, because a usage section is not worth failing a review over.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B11e8TZZxJyzHW7jj7KWUN

tests/pilot/test_webhook_server.py

@@ -134,3 +134,43 @@ def test_missing_label_is_ignored(monkeypatch):
 def test_review_slots_bound_matches_config():
     assert ws.MAX_CONCURRENT >= 1
     assert ws._review_slots._value <= ws.MAX_CONCURRENT
+
+
+# ---------------------------------------------------------------------------
+# AI-USAGE opt-in applied after the triggering label event
+# ---------------------------------------------------------------------------
+
+
+def test_run_review_rereads_labels_for_late_ai_usage(monkeypatch):
+    # Labelling a PR AI-REVIEW then AI-USAGE fires two events; the review
+    # claims on the first, so the second is deduped and the payload snapshot
+    # never sees AI-USAGE. The re-read at review start must recover it.
+    seen = {}
+    monkeypatch.setattr(ws, "_fetch_current_labels",
+                        lambda repo, index: [{"name": "AI-REVIEW"}, {"name": "AI-USAGE"}])
+    monkeypatch.setattr(ws, "review_pr", lambda **kw: seen.update(kw) or True)
+    ws._run_review(("o/r", "9", "abc1234"), "t", "b", False, "main")
+    assert seen["report_usage"] is True
+
+
+def test_run_review_keeps_usage_off_when_label_absent(monkeypatch):
+    seen = {}
+    monkeypatch.setattr(ws, "_fetch_current_labels",
+                        lambda repo, index: [{"name": "AI-REVIEW"}])
+    monkeypatch.setattr(ws, "review_pr", lambda **kw: seen.update(kw) or True)
+    ws._run_review(("o/r", "9", "abc1234"), "t", "b", False, "main")
+    assert seen["report_usage"] is False
+
+
+def test_label_reread_failure_is_not_fatal(monkeypatch):
+    # A dead API must not take the review down with it — the re-read is a
+    # best-effort upgrade of an opt-in flag, nothing more.
+    def _boom(*a, **k):
+        raise OSError("api down")
+    monkeypatch.setattr(ws.urllib.request, "urlopen", _boom)
+    assert ws._fetch_current_labels("o/r", "9") == []
+
+    seen = {}
+    monkeypatch.setattr(ws, "review_pr", lambda **kw: seen.update(kw) or True)
+    ws._run_review(("o/r", "9", "abc1234"), "t", "b", False, "main")
+    assert seen["report_usage"] is False