fix(redis): add opt-in TCP socket keepalive on all client connections (#23571)

Introduces REDIS_SOCKET_KEEPALIVE and wires socket_keepalive=True
through to every Redis client created by get_redis_connection
(plain, cluster and sentinel paths, sync and async). When enabled,
the kernel sends TCP keepalive probes on idle connections so
half-closed sockets (e.g. after a silent firewall/LB reset or a NIC
flap) are detected before the next command lands on them and the
request never sees a "Connection reset by peer" error.

Defaults to off so existing deployments see no behavioural change.
Operators who want the protection set REDIS_SOCKET_KEEPALIVE=true
in their environment.

Co-authored-by: Claude <noreply@anthropic.com>

backend/open_webui/env.py

@@ -426,6 +426,15 @@ try:
 except ValueError:
     REDIS_SOCKET_CONNECT_TIMEOUT = None
 
+# Whether to enable TCP SO_KEEPALIVE on Redis client sockets. Opt-in:
+# defaults to off so behavior is unchanged for existing deployments. When
+# enabled, the kernel sends TCP keepalive probes on idle connections so
+# half-closed sockets (e.g. after a silent firewall/LB reset or a NIC
+# flap) are detected before the next command lands on them.
+REDIS_SOCKET_KEEPALIVE = (
+    os.environ.get('REDIS_SOCKET_KEEPALIVE', 'False').lower() == 'true'
+)
+
 REDIS_RECONNECT_DELAY = os.environ.get('REDIS_RECONNECT_DELAY', '')
 
 if REDIS_RECONNECT_DELAY == '':