refactor(backend/copilot): replace manual NX-poll loop with redis-py built-in Lock in _get_session_lock

autogpt_platform/backend/backend/copilot/model.py

@@ -1,4 +1,3 @@
-import asyncio
 import logging
 import uuid
 from contextlib import asynccontextmanager
@@ -848,25 +847,21 @@ async def update_session_title(
 
 @asynccontextmanager
 async def _get_session_lock(session_id: str) -> AsyncIterator[None]:
-    """Distributed Redis NX lock for a session, usable as an async context manager.
+    """Distributed Redis lock for a session, usable as an async context manager.
 
-    Retries every 50ms for up to 2s so a waiter behind a concurrent writer keeps
-    polling until the lock is free. The lock is always released explicitly on exit;
-    the 10s TTL is a crash-safety net so a dead pod never holds it indefinitely.
+    Uses redis-py's built-in Lock (Lua-script acquire/release) so lock acquisition
+    is atomic and release is owner-verified. Blocks up to 2s for a concurrent
+    writer to finish; the 10s TTL ensures a dead pod never holds the lock forever.
     On Redis failure the lock is skipped with a warning — callers should still
     apply an idempotency check as a fallback.
     """
     _lock_key = f"copilot:session_lock:{session_id}"
-    _redis = None
+    lock = None
     acquired = False
     try:
         _redis = await get_redis_async()
-        deadline = asyncio.get_event_loop().time() + 2.0
-        while asyncio.get_event_loop().time() < deadline:
-            if await _redis.set(_lock_key, "1", nx=True, ex=10):
-                acquired = True
-                break
-            await asyncio.sleep(0.05)
+        lock = _redis.lock(_lock_key, timeout=10, blocking_timeout=2)
+        acquired = await lock.acquire(blocking=True)
         if not acquired:
             logger.warning(
                 "Could not acquire session lock for %s within 2s", session_id
@@ -877,8 +872,8 @@ async def _get_session_lock(session_id: str) -> AsyncIterator[None]:
     try:
         yield
     finally:
-        if acquired and _redis is not None:
+        if acquired and lock is not None:
             try:
-                await _redis.delete(_lock_key)
+                await lock.release()
             except Exception:
                 pass  # TTL will expire the key