feat: add skill validation improvements

[neubig]

Summary

This PR adds validation improvements for skills, following the AgentSkills standard.

Changes

1. Export validate_skill_name in Public API

from openhands.sdk.context.skills import validate_skill_name

errors = validate_skill_name("my-skill")
if errors:
    print("Invalid skill name:", errors)

2. Description Length Validation

Pydantic validator enforces max 1024 characters per AgentSkills spec:

from openhands.sdk.context.skills import Skill

# This will raise SkillValidationError
skill = Skill(name="test", content="...", description="x" * 1025)

Backward Compatibility

• All changes are backward compatible
• New exports are additive

Testing

Added 2 tests for description length validation.

Related Issues

Part of #1473 (Support AgentSkills standard)

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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:python3.12-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:b7b1667-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-b7b1667-python \
  ghcr.io/openhands/agent-server:b7b1667-python

All tags pushed for this build

ghcr.io/openhands/agent-server:b7b1667-golang-amd64
ghcr.io/openhands/agent-server:b7b1667-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:b7b1667-golang-arm64
ghcr.io/openhands/agent-server:b7b1667-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:b7b1667-java-amd64
ghcr.io/openhands/agent-server:b7b1667-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:b7b1667-java-arm64
ghcr.io/openhands/agent-server:b7b1667-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:b7b1667-python-amd64
ghcr.io/openhands/agent-server:b7b1667-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-amd64
ghcr.io/openhands/agent-server:b7b1667-python-arm64
ghcr.io/openhands/agent-server:b7b1667-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-arm64
ghcr.io/openhands/agent-server:b7b1667-golang
ghcr.io/openhands/agent-server:b7b1667-java
ghcr.io/openhands/agent-server:b7b1667-python

About Multi-Architecture Support

• Each variant tag (e.g., b7b1667-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., b7b1667-python-amd64) are also available if needed

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
openhands-sdk/openhands/sdk/context/skills
skill.py	281	203	27%	64, 68–69, 73–74, 78–79, 181–182, 185, 191–197, 203–207, 213–220, 248, 250–251, 253–254, 256, 267–268, 270–273, 276, 279–281, 286–289, 292–295, 297, 313–315, 318–319, 323, 325–328, 331, 334–336, 338, 364, 367, 375, 380–382, 388, 390–396, 399, 410–411, 422, 439, 441–442, 454–455, 460, 467, 477–478, 480, 486–487, 489, 498–501, 503–506, 514–516, 524–526, 549–550, 552–555, 558–559, 562–564, 567–568, 573–574, 579–580, 584–585, 591, 612–613, 615–618, 620–622, 627–631, 633, 637–638, 640, 643, 661–662, 664–665, 668, 673–675, 678, 680–682, 687–691, 693, 698–699, 703, 706, 745, 747, 749–750, 752–754, 757–760, 763, 765, 768–770, 774–780, 782–783, 785, 788
TOTAL	14646	6961	52%

[juanmichelini]

LGTM!