fix: override server_image default to None in DockerDevWorkspace

[simonrosenberg]

Summary

• DockerDevWorkspace inherits server_image's default of "ghcr.io/openhands/agent-server:latest-python" from DockerWorkspace, causing the _validate_images validator to reject any instance constructed with only base_image (both fields are non-None).
• Override the server_image field default to None in DockerDevWorkspace so callers can use base_image without needing to explicitly pass server_image=None.
• This is the SDK-side fix for the workaround applied downstream in OpenHands/benchmarks@63cb3a1.

Fixes #2242

Breaking change note

DockerDevWorkspace() called without base_image previously inherited the parent's server_image default ("ghcr.io/openhands/agent-server:latest-python") and passed validation. After this change, it will raise a ValueError since both fields default to None.

This is unlikely to affect anyone in practice — using DockerDevWorkspace without base_image is not a meaningful use case (you'd use DockerWorkspace directly instead). All existing usages in the SDK and benchmarks repos pass base_image explicitly. The previous behavior was accidentally permissive, not intentional.

Test plan

• Existing tests pass (test_docker_dev_workspace_has_build_fields, test_docker_dev_workspace_import, etc.)
• DockerDevWorkspace(base_image="python:3.13") no longer raises a validation error
• DockerDevWorkspace(server_image="ghcr.io/openhands/agent-server:latest") still works
• DockerDevWorkspace() (neither field) raises a validation error as expected

🤖 Generated with Claude Code

---

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:e27b76e-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-e27b76e-python \
  ghcr.io/openhands/agent-server:e27b76e-python

All tags pushed for this build

ghcr.io/openhands/agent-server:e27b76e-golang-amd64
ghcr.io/openhands/agent-server:e27b76e-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:e27b76e-golang-arm64
ghcr.io/openhands/agent-server:e27b76e-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:e27b76e-java-amd64
ghcr.io/openhands/agent-server:e27b76e-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:e27b76e-java-arm64
ghcr.io/openhands/agent-server:e27b76e-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:e27b76e-python-amd64
ghcr.io/openhands/agent-server:e27b76e-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-amd64
ghcr.io/openhands/agent-server:e27b76e-python-arm64
ghcr.io/openhands/agent-server:e27b76e-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-arm64
ghcr.io/openhands/agent-server:e27b76e-golang
ghcr.io/openhands/agent-server:e27b76e-java
ghcr.io/openhands/agent-server:e27b76e-python

About Multi-Architecture Support

• Each variant tag (e.g., e27b76e-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., e27b76e-python-amd64) are also available if needed

[github-actions]

API breakage checks (Griffe)

Result: Failed

Log excerpt (first 1000 characters)

============================================================
Checking openhands-sdk (openhands.sdk)
============================================================
Comparing openhands-sdk 1.11.5 against 1.11.4
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): load_public_skills
No breaking changes detected

============================================================
Checking openhands-workspace (openhands.workspace)
============================================================
Comparing openhands-workspace 1.11.5 against 1.11.4
::warning file=openhands-workspace/openhands/workspace/docker/dev_workspace.py,line=33,title=DockerDevWorkspace.server_image::Attribute value was changed: `Field(default='ghcr.io/openhands/agent-server:latest-python', description='Pre-built agent server image to use.')` -> `Field(default=None, description='Pre-built agent server image. Mutually exclusive with base_image.')`
::error title=SemVer::Breaking changes detected (1); re

Action log

[github-actions]

Agent server REST API breakage checks (OpenAPI)

Result: Passed

Action log

[all-hands-bot]

🟢 Good taste - Simple, elegant fix for a real problem. Overriding the inherited field default is the right approach here. LGTM!

[enyst]

@simonrosenberg Please see the linked PR comment, the Griffe check for API breakages failed on this PR. The way we do this is to use deprecation mechanism for a few releases, before breaking changes. WDYT?