fix(cancelled-trace bug): quiet ConnectionClosedOK on HUDRuntime tunnel close

[lukass16]

Part of the HUDRuntime cancelled-trace bug (counterpart: https://github.com/hud-evals/hud-monorepo/pull/2144). Low priority, draft. Supersedes #692, which GitHub closed when its branch was renamed.

What

When the HUD runtime gateway closes a tunnel websocket normally (code 1000) while the local side is still relaying, _splice_websocket re-raised websockets.ConnectionClosedOK out of the asyncio.start_server callback, so asyncio logged it as an unhandled exception even though nothing failed.

_splice_websocket now treats ConnectionClosedOK as a clean end of the relay. All other relay errors still propagate.

Scope

SDK-only log-noise fix. It does not fix the platform marking local-agent HUDRuntime traces cancelled; that is the separate monorepo PR (runtime-session DELETE cancels the still-running attached trace before /trace/{id}/exit arrives). Independent of any other open PR; based on main.

Tests

• New test_splice_websocket_treats_normal_close_as_clean_end fails on main, passes here.
• hud/eval/tests/test_hosted.py: 41 passed; ruff format/check and ty clean.

---

Note

Low Risk
SDK-only logging/exception-handling tweak in the websocket relay path; real relay failures still propagate.

Overview
HUDRuntime tunnel relay no longer surfaces websockets.ConnectionClosedOK as an unhandled error when the gateway closes the tunnel websocket normally (close code 1000) during TCP↔WS splicing.

_splice_websocket still re-raises every other relay exception; only a normal close is swallowed so asyncio does not log a spurious failure.

Adds test_splice_websocket_treats_normal_close_as_clean_end alongside the existing relay-error propagation test.

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T19:41:06.265472Z	56bbd62	Draft marked ready

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[chatgpt-codex-connector]

Exercise the normal runtime connection lifecycle

This regression test calls the private _splice_websocket helper directly, bypassing _forward_runtime_connection and the asyncio.start_server callback where the reported unhandled exception is observable. It therefore does not verify that a normal gateway close completes cleanly through the actual runtime lifecycle; mock the websocket boundary while driving a HUDRuntime connection instead.

AGENTS.md reference: AGENTS.md:L126-L132

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