feat: add Antigravity CLI (agy) support

[Joseph19820124]

Summary

• Add Dockerfile.antigravity — downloads the native agy binary from Google Storage, supports linux/amd64 and linux/arm64
• Add commented [agent] block in config.toml.example for agy --acp
• Add commented antigravity agent example in charts/openab/values.yaml
• Update AGENTS.md Dockerfile count 7 → 8

Background

Google Antigravity CLI (agy) is Google's terminal-first coding agent, the successor to @google/gemini-cli. It supports ACP via agy --acp and authenticates via Google Sign-In (OAuth — no API key needed).

The binary is distributed as a native pre-compiled binary from Google Storage:

https://storage.googleapis.com/antigravity-public/antigravity-cli/<version>/<arch>/<file>

Test plan

• docker build -f Dockerfile.antigravity . on amd64
• docker build -f Dockerfile.antigravity . on arm64
• Inside container: agy auth → complete Google Sign-In, then agy --acp launches ACP session
• helm template test charts/openab passes with antigravity example uncommented in values.yaml

🤖 Generated with Claude Code

[github-actions]

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[Joseph19820124]

Closing: verified locally that agy --acp does not exist in v1.0.0 (flag undefined). Need to investigate if an ACP adapter exists before re-opening.

[Joseph19820124]

Reopening with a real working implementation.

Root cause of the original close: agy v1.0.0 has no native --acp flag — the assumption was wrong.

Fix: Added agy-acp/agy-acp.mjs — a thin Node.js ACP stdio adapter that translates the openab JSON-RPC protocol into agy --print invocations.

Verified locally with end-to-end test (mock agy):

✓ initialize: agy v1.0.0
✓ session/new: sessionId = 15122cc8-...
✓ agent_message_chunk (prompt 1): "Hello! You said: what is 2+2?"
✓ session/prompt [1] complete
✓ agent_message_chunk (prompt 2 --continue): "[continued session] You said: and what is 3+3?"
✓ session/prompt [2] complete
✅ All ACP protocol steps passed.

Config is now:

[agent]
command = "node"
args = ["/usr/local/lib/agy-acp.mjs"]

[Joseph19820124]

Closing.

[shaun-agent]

Thanks for putting this together — the Antigravity ACP bridge idea is interesting, and it is useful as an experiment.

After reviewing the diff, my read is:

• The touched Rust core files (src/acp/connection.rs, src/adapter.rs, src/discord.rs, src/main.rs) appear to be formatting-only changes, not meaningful behavior changes.
• The real functional addition is the new agy-acp/agy-acp.mjs wrapper plus Dockerfile.antigravity, Helm values, and config examples.
• The main risk is not the Rust diff. It is adding another officially-supported runtime image around a custom, hand-rolled ACP bridge.

Specific concerns:

• Dockerfile.antigravity downloads the Antigravity CLI binary directly from Google Storage without checksum or signature verification. We do have similar direct-download risk in some existing agent images, so this is not unique to this PR, but it is still a supply-chain surface we should avoid expanding casually.
• The binary/wrapper would run in the agent pod and may have access to repo files, mounted volumes, env, GitHub auth, and Discord context depending on deployment.
• agy-acp.mjs only approximates ACP behavior: cancellation is a no-op, sessions are mapped to agy --continue, and streaming/error semantics may not match native ACP expectations.
• Adding it to the chart/config examples makes this look like an officially supported agent. That creates operational and maintenance burden, especially if Antigravity ships native ACP soon.

Recommendation: I would not merge this into main as-is. It is reasonable to use/test this locally or in personal infra from a branch/private image, ideally with limited tokens and a test Discord channel. For upstream, I would wait for native ACP support or a more hardened integration with checksum/provenance verification and clearer support boundaries.

So: useful experiment, but not something I think openab should support in-tree yet.