Validator client head monitor timeout fix

[michaelsproul]

Issue Addressed

Fix a bug in v8.1.0 whereby the VC times out continuously with:

Feb 18 02:03:48.030 WARN Head service failed retrying starting next slot error: "Head monitoring stream error, node: 0, error: SseClient(Transport(reqwest::Error { kind: Decode, source: reqwest::Error { kind: Body, source: TimedOut } }))"

Proposed Changes

• Remove the existing timeout for the events API by using Duration::MAX. This is necessary as the client is configured with a default timeout. This is the only way to override/remove it.
• DO NOT add a read_timeout (yet), as this would need to be configured on a per-client basis. We do not want to create a new Client for every call as the early commits on this branch were doing, as this would bypass the TLS cert config, and is also wasteful.

Additional Info

Awaiting confirmation that this fix works after manual testing. Will update.

[michaelsproul]

Can confirm that manual testing on a VC shows that the timeout is gone (tested commit cc1d64d).

[jimmygchen]

Nice!

[michaelsproul]

Can also confirm that stopping one of the attached VCs results in:

Feb 18 04:22:09.149 WARN Head service failed retrying starting next slot error: "Head monitoring stream error, node: 0, error: SseClient(StreamEnded)"

[mergify]

Merge Queue Status

Rule: default

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• ✅ Entered queue — 2026-02-18 04:55 UTC
• ✅ Checks passed · on draft merge queue: embarking release-v8.1 (c5b4580) and #8846 together #8852
• ✅ Merged — 2026-02-18 05:28 UTC · at 513f598e3a82cedb38e486ad276400a55a6c4bd2

This pull request spent 32 minutes 39 seconds in the queue, including 31 minutes 2 seconds running CI.

Required conditions to merge

• check-success=local-testnet-success
• check-success=test-suite-success