feat(gateway): process inbound events through the agent

surfsense_backend/app/gateway/thread_lock.py

@@ -0,0 +1,40 @@
+"""Redis-backed distributed locks for gateway conversation turns."""
+
+from __future__ import annotations
+
+import logging
+
+import redis
+
+from app.config import config
+from app.observability.metrics import record_gateway_thread_lock_contention
+
+logger = logging.getLogger(__name__)
+
+_redis_client: redis.Redis | None = None
+
+
+def _redis() -> redis.Redis:
+    global _redis_client
+    if _redis_client is None:
+        _redis_client = redis.from_url(config.REDIS_APP_URL, decode_responses=True)
+    return _redis_client
+
+
+def _lock_key(thread_id: int) -> str:
+    return f"gateway:thread_lock:{thread_id}"
+
+
+def acquire_thread_lock(thread_id: int, ttl: int = 60) -> bool:
+    acquired = bool(_redis().set(_lock_key(thread_id), "1", nx=True, ex=ttl))
+    if not acquired:
+        record_gateway_thread_lock_contention()
+    return acquired
+
+
+def release_thread_lock(thread_id: int) -> None:
+    try:
+        _redis().delete(_lock_key(thread_id))
+    except redis.RedisError as exc:
+        logger.warning("Failed to release gateway thread lock for %s: %s", thread_id, exc)
+