[404Wolf]

Why

Prod incident 2026-09-23 14:12:10Z: the connection-gateway's redis pub/sub subscriber (poll_messages) exited on all three prod instances and never came back. It was a bare tokio::spawn whose exit was a trace-level log, so nothing noticed. From then on every websocket message that had to cross gateway instances was dropped — ~2/3 of all realtime with 3 instances. Live agent sessions showed "Working…" forever (the fold never received the reply/turn-end frames); a reload fixed each one because GET /log is durable.

Evidence (Datadog, prod): connection_gateway.redis_publish continued at ~500 / 10 min while connection_gateway.redis_dispatch went from ~1175/hour to 0 after 14:12:10.826Z; fully retained publish traces after that have no dispatch children.

What

• poll_messages now supervises the subscription: when a run ends (stream closed by Redis) or fails (connect/subscribe error) it logs at error level and resubscribes after an exponential backoff (1 s → 30 s, reset once a subscription has lived a minute).
• The subscribe itself logs at info so a resubscribe is visible.
• No behaviour change on the hot path; the forwarding loop is unchanged, just moved into subscribe_and_forward.

Not in this PR (follow-ups)

• Alert on redis_publish > 0 && redis_dispatch == 0; make relay liveness part of the health check.
• Client-side gap detection + resync() in the agent session fold so a lossy socket heals without a reload.
• Immediate remediation for today is still a force-new-deployment of prod connection-gateway; this PR only prevents the next one.

Testing

• cargo check -p connection_gateway and cargo clippy -p connection_gateway (SQLX_OFFLINE) pass, cargo fmt applied.
• Not exercised against a live Redis drop; the change is a supervisor loop around the unchanged forwarding code.

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Note

Medium Risk
Changes lifecycle of the Redis pub/sub relay in connection-gateway (realtime cross-instance messaging), though the per-message forwarding path is untouched.

Overview
Fixes silent loss of cross-instance websocket relay when Redis drops the pub/sub subscriber: poll_messages no longer runs a single subscribe-and-forward pass that exits quietly.

It now supervises the relay in an endless loop—on stream end or connect/subscribe failure it logs at error, waits with exponential backoff (1s → 30s, reset after a subscription lasts 60s), then opens a new subscription. The actual message forwarding is unchanged and lives in new subscribe_and_forward; successful subscribes log at info so recovery is visible in logs.

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Improved the reliability of real-time message delivery. If the message connection is interrupted, the service now retries automatically, with retry intervals that adjust over time and reset after a sustained connection.

Walkthrough

poll_messages now continuously retries Redis subscriptions that end or fail. The retry delay starts at one second, doubles up to 30 seconds, and resets to one second after a subscription lasts at least 60 seconds. The new subscribe_and_forward helper handles subscription setup and message forwarding, and returns contextual errors for connection or channel-subscription failures. poll_messages no longer returns a Result.

Merge Risk: 🟡 Moderate · up to 99836

The change restarts the Redis relay when its stream ends or fails. However, if Redis accepts a connection and then stops responding during setup, the gateway can wait forever and never retry. Cross-instance websocket messages would then stay undelivered, which is the same incident this PR aims to fix. Add setup and subscribe timeouts before merging.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Title check	⚠️ Warning	The title uses conventional commit format and accurately describes the Redis resubscription change, but it is 73 characters long and exceeds the 72-character limit.	Shorten the title to 71 characters or fewer while preserving the conventional commit format and meaning.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the production incident, the Redis subscription supervision change, backoff behavior, testing, and follow-up work.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@services/connection_gateway/src/service/redis.rs`:
- Line 89: Update subscribe_and_forward to apply deadlines to get_async_pubsub
connection setup and PubSubSink::subscribe acknowledgement, returning contextual
timeout errors to the retry loop. Do not apply a timeout to the long-lived
forwarding stream.

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• services/connection_gateway/src/service/redis.rs

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