The live-dashboard WS client (src/hooks/useLiveDashboard.ts) only sent a
subscribe frame on open and never emitted the protocol's { type: "ping" }
heartbeat. The server (src/server/ws/liveServer.ts) refreshes client
liveness only from inbound messages and terminates any client idle past
HEARTBEAT_TIMEOUT_MS (35s), so a healthy, connected-but-idle dashboard
client was force-terminated roughly every 35-45s, causing constant
reconnect churn (#10319).
Fix (both directions, per the analyzed plan):
- Client: start a 15s ping interval on open, cleared on close/unmount/
reconnect, so the connection stays inside the server's liveness window.
- Server (defense in depth): the outbound heartbeat pong now also bumps
client.lastActivity, so even a third-party client that never pings is
not dropped for being idle.
Regression coverage:
- tests/unit/useLiveDashboard-heartbeat.test.tsx: fast fake-timer check
that the hook emits periodic ping frames and cleans up the interval on
close/unmount (no leaked timers).
- tests/integration/live-ws-heartbeat-keepalive.test.ts: real WS-server
integration test asserting a silent-but-subscribed client stays
connected past the 35s heartbeat timeout (~50s window), converted from
the plan file's TDD RED repro.
Closes#10319
55e8b26ace