feat(sdk): register Pi as a built-in ACP provider and pre-install pi-acp in agent-server Docker image

[Deep070203]

HUMAN:

Resolves OpenHands/OpenHands#16204 by adding first-class upstream support for the Pi ACP coding agent in the SDK provider registry (ACP_PROVIDERS) and pre-installing pi-acp in the openhands-agent-server base Docker image.
This allows Pi to be selected as a native ACP server discriminator (acp_server: "pi"), matching the behavior of claude-code, codex, and gemini-cli.

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AGENT:

Why

Per review on OpenHands PR #16229 and issue OpenHands/OpenHands#16204, pi should not rely on frontend-only custom command spoofing or docker-mode hacks in agent-canvas. Instead, pi needs first-class upstream support in software-agent-sdk (alongside claude-code, codex, and gemini-cli) so that downstream clients and agent-server Docker containers get native Pi ACP support automatically.

Summary

• Registered "pi" in ACPServerKind discriminator union and ACP_PROVIDERS registry (display_name="Pi", default_command=("npx", "-y", "pi-acp@0.0.33"), binary_name="pi-acp", data_dir_env_var="PI_CODING_AGENT_DIR").
• Pre-installed pi-acp@0.0.33 and created PATH wrappers under /usr/local/bin/ in openhands-agent-server Dockerfile.
• Added comprehensive unit test coverage for registry metadata, command resolution, and per-conversation data directory isolation.

Issue Number

OpenHands/OpenHands (#16204)

How to Test

1. Run the SDK unit test-suite

uv run pytest tests/sdk/settings/test_acp_providers.py tests/sdk/test_settings.py tests/sdk/agent/test_acp_agent.py

2. Build and verify the local Docker image:

docker build -f openhands-agent-server/openhands/agent_server/docker/Dockerfile -t openhands-agent-server:pi-test .
docker run --rm --entrypoint /bin/sh openhands-agent-server:pi-test -c "which pi-acp"

Video/Screenshots

Type

• Bug fix
• Feature
• Refactor
• Breaking change
• Docs / chore

Notes

Requires a bump in @openhands/typescript-client once released to expose "pi" to agent-canvas.

[Deep070203]

@VascoSch92 can you take a look and test and let me know if everything is working correctly.

[VascoSch92]

why default here?

[Deep070203]

Unlike Claude Code, Codex, or Gemini CLI, pi-acp manages model resolution internally or via environment configuration.
Setting id="default" with default_model="default" allows the SDK to pass a clean, non-null model option while letting pi-acp use its native default engine setup

[VascoSch92]

left some comments. Perhaps look on what other ACP are doing.

Thanks :-)

[Deep070203]

@VascoSch92 resolved the comments. Check and let me know!