Fix websocket disconnect handling to avoid server shutdown

[simonrosenberg]

Summary

This PR fixes the secondary issue from #1633: websocket disconnect handling that could potentially cause server instability.

Problem

When websocket connections encountered ConnectionError, these exceptions were being re-raised along with RuntimeError, which could potentially cause server instability.

Solution

Modified websocket handlers to:

• Handle ConnectionError gracefully (connection-related errors are safe to suppress)
• Keep re-raising RuntimeError to surface actual bugs (as suggested in code review)
• Use explicit except ConnectionError clause instead of isinstance check (cleaner)

Changes

• sockets.py: Modified events_socket and bash_events_socket to handle ConnectionError gracefully while still re-raising RuntimeError
• test_event_router_websocket.py: Updated test to verify RuntimeError is still re-raised

Checklist

• If the PR is changing/adding functionality, are there tests to reflect this?
• If there is an example, have you run the example to make sure that it works?
• If there are instructions on how to run the code, have you followed the instructions and made sure that it works?
• If the feature is significant enough to require documentation, is there a PR open on the OpenHands/docs repository with the same branch name?
• Is the github CI passing?

Fixes #1633 (partial - websocket disconnect fix)

---

Agent Server images for this PR

• GHCR package: https://github.com/OpenHands/agent-sdk/pkgs/container/agent-server

Variants & Base Images

Variant	Architectures	Base Image	Docs / Tags
java	amd64, arm64	eclipse-temurin:17-jdk	Link
python	amd64, arm64	nikolaik/python-nodejs:python3.12-nodejs22	Link
golang	amd64, arm64	golang:1.21-bookworm	Link

Pull (multi-arch manifest)

# Each variant is a multi-arch manifest supporting both amd64 and arm64
docker pull ghcr.io/openhands/agent-server:f2091f2-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-f2091f2-python \
  ghcr.io/openhands/agent-server:f2091f2-python

All tags pushed for this build

ghcr.io/openhands/agent-server:f2091f2-golang-amd64
ghcr.io/openhands/agent-server:f2091f2-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:f2091f2-golang-arm64
ghcr.io/openhands/agent-server:f2091f2-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:f2091f2-java-amd64
ghcr.io/openhands/agent-server:f2091f2-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:f2091f2-java-arm64
ghcr.io/openhands/agent-server:f2091f2-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:f2091f2-python-amd64
ghcr.io/openhands/agent-server:f2091f2-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-amd64
ghcr.io/openhands/agent-server:f2091f2-python-arm64
ghcr.io/openhands/agent-server:f2091f2-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-arm64
ghcr.io/openhands/agent-server:f2091f2-golang
ghcr.io/openhands/agent-server:f2091f2-java
ghcr.io/openhands/agent-server:f2091f2-python

About Multi-Architecture Support

• Each variant tag (e.g., f2091f2-python) is a multi-arch manifest supporting both amd64 and arm64
• Docker automatically pulls the correct architecture for your platform
• Individual architecture tags (e.g., f2091f2-python-amd64) are also available if needed

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
openhands-agent-server/openhands/agent_server
sockets.py	105	55	47%	50–51, 57–59, 68–70, 76–78, 84, 87, 91–93, 95–96, 110–111, 113–114, 116–118, 121, 123–126, 128–129, 131–135, 138–140, 143, 147–149, 151–152, 155, 162–163, 177–181, 191
TOTAL	14788	7098	52%

[all-hands-bot]

[Automatic Post]: This PR seems to be currently waiting for review. @tofarr, could you please take a look when you have a chance?