fix: prevent agent server crash on tmux session creation failure

[hieptl]

Summary

[fill in a summary of this PR]

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?

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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:python3.13-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:5a278ab-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-5a278ab-python \
  ghcr.io/openhands/agent-server:5a278ab-python

All tags pushed for this build

ghcr.io/openhands/agent-server:5a278ab-golang-amd64
ghcr.io/openhands/agent-server:5a278ab-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:5a278ab-golang-arm64
ghcr.io/openhands/agent-server:5a278ab-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:5a278ab-java-amd64
ghcr.io/openhands/agent-server:5a278ab-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:5a278ab-java-arm64
ghcr.io/openhands/agent-server:5a278ab-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:5a278ab-python-amd64
ghcr.io/openhands/agent-server:5a278ab-nikolaik_s_python-nodejs_tag_python3.13-nodejs22-amd64
ghcr.io/openhands/agent-server:5a278ab-python-arm64
ghcr.io/openhands/agent-server:5a278ab-nikolaik_s_python-nodejs_tag_python3.13-nodejs22-arm64
ghcr.io/openhands/agent-server:5a278ab-golang
ghcr.io/openhands/agent-server:5a278ab-java
ghcr.io/openhands/agent-server:5a278ab-python

About Multi-Architecture Support

• Each variant tag (e.g., 5a278ab-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., 5a278ab-python-amd64) are also available if needed