Desktop/dashboard WebSocket connections drop during long agent operations
(delegate_task subagents, large model outputs) when the uvicorn event loop is
GIL-starved for minutes. Root cause: uvicorn's ws keepalive ping runs on the
SAME event loop as agent turns. A single synchronous GIL-holding call on a
worker thread (a regex/scrub over a large output, or a long subagent turn)
freezes the loop, so it cannot process the incoming pong within ws_ping_timeout
and uvicorn closes an otherwise-healthy connection (#53773: 'event loop stalled
226.3s'; #48445/#50005). Loosening the timeout only raises the threshold — a
multi-minute stall sails past any finite window.
The keepalive ping exists to detect half-open connections (reverse-proxy 524,
dropped tunnels), which cannot happen on loopback: there is no network or proxy
in the path, and a dead local client tears the socket down with a real FIN/RST
that starlette surfaces as WebSocketDisconnect regardless of the ping. So on
loopback the ping provides ~no liveness value while actively killing
recoverable stalls — disable it entirely (ws_ping_interval/timeout=None).
Non-loopback (public) binds sit behind a Cloudflare Tunnel where half-open IS a
real failure mode, so the ping stays at 20/20 to detect it.
Empirically verified (real uvicorn + websockets peer): with ws_ping=None the
server never closes a silent peer during an 8s window; with the pre-fix 2s/2s
window uvicorn closes it. A genuinely-dead client still fires the
WebSocketDisconnect reap path regardless of the ping.
Note: this fixes the local Desktop case (the OP's scenario). A remote Desktop
over an authenticated public dashboard route (McCalebTheSecond's comment) keeps
the ping and needs the deeper GIL-hotspot fix — tracked separately.
Closes#53773
kshitijk4poor
e73adb5043