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

pilot/webhook_server.py

@@ -39,6 +39,7 @@ import hmac
 import json
 import os
 import threading
+import urllib.request
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 
 from ai_review import review_pr
@@ -176,10 +177,46 @@ def _release(key: tuple[str, str, str]) -> None:
         _inflight.discard(key)
 
 
+def _fetch_current_labels(repo: str, index: str) -> list:
+    """Re-read the PR's labels from the API. [] on any failure.
+
+    The webhook payload is a snapshot from the instant the event fired. When a
+    PR is labelled AI-REVIEW first and AI-USAGE a moment later, the review is
+    already claimed and running, so the second event is deduped and the usage
+    opt-in is lost — the review posts without its usage block. Reading the
+    labels again at review start closes that window.
+    """
+    url = f"{GITEA_API}/repos/{repo}/issues/{index}/labels"
+    req = urllib.request.Request(url, headers={
+        "Authorization": f"token {BOT_TOKEN}",
+        "Accept": "application/json",
+    })
+    try:
+        with urllib.request.urlopen(req, timeout=15) as resp:
+            return json.loads(resp.read().decode() or "[]")
+    except Exception as e:
+        print(f"pragent-webhook: could not re-read labels for {repo}#{index}: {e}", flush=True)
+        return []
+
+
 def _run_review(
     key: tuple[str, str, str], title: str, body: str, report_usage: bool, base_ref: str
 ) -> None:
     repo, index, sha = key
+    # The AI-USAGE opt-in may have been applied *after* the label event that
+    # triggered this review (labelling is two events, the review claims on the
+    # first). Re-read the labels now so the later opt-in still counts.
+    if not report_usage:
+        report_usage = _labels_have(
+            _fetch_current_labels(repo, index), AI_USAGE_LABEL
+        )
+        if report_usage:
+            print(
+                f"pragent-webhook: {repo}#{index} AI-USAGE found on re-read "
+                f"(added after the trigger event)",
+                flush=True,
+            )
+
     try:
         with _review_slots:
             ok = review_pr(