feat(ADM-018): completed feature

work/artifacts/F-023/security.json

@@ -0,0 +1,13 @@
+{
+  "feature_id": "F-023",
+  "agent": "security",
+  "verdict": "APPROVED",
+  "summary": "Security approved. No new dependencies. Webhook signature is verified with constant-time HMAC and 5-minute tolerance. Idempotency is enforced at the database level by the unique constraint on (provider, provider_event_id).",
+  "evidence": [
+    "cd project && npm audit --audit-level=high --omit=dev: found 0 vulnerabilities",
+    "Reviewed StripePaymentProvider: uses createHmac and timingSafeEqual with bounded timestamp tolerance",
+    "Reviewed payments_transactions table: UNIQUE (provider, provider_event_id) and CHECK constraints",
+    "Reviewed webhook route: unauthenticated and signature-validated; no client payment status fields accepted"
+  ],
+  "timestamp": "2026-08-15T18:37:54Z"
+}