The SSE event stream could silently die from network partitions, NAT
table flushes, browser tab throttling, or server restarts. When this
happened:
1. The `error` callback only called `captureException` — no reconnection
was triggered
2. The `complete` callback was `() => {}` — a cleanly terminated stream
left the client permanently broken
3. No mechanism existed to detect a silently dead connection where no
FIN/RST was received
## Summary
- **Fix `error`/`complete` callbacks**: The `graphql-sse` subscription's
`error` callback only reported to Sentry, and `complete` was a no-op.
Both now set `shouldDestroyEventStreamState = true` to trigger the
destroy-recreate lifecycle, ensuring detected transport failures and
clean stream terminations lead to automatic reconnection.
- **Add server-side keepalive**: The existing heartbeat timer now runs
every 30s (instead of 6min) and publishes empty events through the Redis
pub/sub channel in addition to refreshing the Redis TTL (throttled to
~6min). Unlike GraphQL Yoga's opaque SSE comment pings, these are real
subscription events that flow through the client's `next`/`message`
handlers.
- **Add client-side keepalive monitor (`SSEKeepAliveEffect`)**: Tracks
the timestamp of the last received event. If no event arrives within 90
seconds (3x the keepalive interval), it clears query listeners and
triggers a stream destroy-recreate cycle.
## Test plan
- [x] Start the app, verify SSE events flow normally (workflow runs
update in real-time)
- [x] Leave the app idle for >90 seconds, then trigger a workflow run —
verify the stream auto-reconnects and events are delivered
- [x] Kill the server, restart it, verify the frontend recovers its
event stream
- [x] Verify keepalive events (empty
`objectRecordEventsWithQueryIds`/`metadataEvents`) appear in browser
network tab every ~30s
- [x] Verify no regressions in SSE-dependent features (record updates,
metadata changes, workflow run visualization)
