opencode-agy

An OpenCode provider plugin for Google's official Antigravity ACP server.

OpenCode → loopback Anthropic Messages proxy → ACP JSON-RPC client →
agy_acp_server.par

Requirements

• OpenCode;
• Bun;
• Google's agy_acp_server.par and the accompanying localharness_external;
• an authenticated ACP server session.

The official server is listed in the ACP Registry.

Install

Download the ACP server archive for your platform. Keep these files together:

agy_acp_server.par
localharness_external

Set the server path, or put it on PATH:

export OPENCODE_AGY_ACP_PATH=/absolute/path/to/agy_acp_server.par

On Linux the registry argument --uid= is supplied automatically. Custom arguments can be provided as JSON:

export OPENCODE_AGY_ACP_ARGS='["--uid="]'

Register the plugin in ~/.config/opencode/opencode.jsonc:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@rasyid_rafi/opencode-agy"]
}

Restart OpenCode after changing plugin configuration.

Authentication

The ACP server advertises these methods:

• oauth-personal;
• oauth-business;
• gemini-api-key;
• agent-platform.

Use the provider authentication action in OpenCode, or set a method for the next ACP worker:

export OPENCODE_AGY_ACP_AUTH_METHOD=oauth-personal

The plugin reuses the official CLI's existing OAuth login when it finds ~/.gemini/antigravity-cli/antigravity-oauth-token (or the equivalent path under GEMINI_HOME). It seeds the ACP server's local credential file so the first OpenCode request does not start a second browser login. Credentials stay on the local machine and are not sent through the OpenCode proxy.

Configuration

| Variable | Purpose | |---|---| | OPENCODE_AGY_ACP_PATH | ACP server executable path | | OPENCODE_AGY_ACP_ARGS | JSON array of ACP server arguments | | OPENCODE_AGY_ACP_AUTH_METHOD | ACP authentication method | | OPENCODE_AGY_ACP_PERMISSION=allow-always\|allow-once\|deny | Automatic ACP permission response; default allow-always | | OPENCODE_AGY_MODE=plan\|accept-edits | ACP session mode when advertised | | OPENCODE_AGY_PROXY_PORT | Loopback proxy port; default ephemeral | | OPENCODE_AGY_DATA_DIR | Session metadata and request replay directory | | OPENCODE_AGY_DEBUG=1 | Metadata-only debug logging | | OPENCODE_AGY_MAX_REQUEST_BYTES | Maximum request size | | OPENCODE_AGY_TURN_STALL_MS | Idle timeout after the last ACP session update | | OPENCODE_AGY_PRINT_TIMEOUT_MS | Setup/request timeout, not a streamed-turn limit | | OPENCODE_AGY_IDLE_WORKER_MS | Idle session cleanup interval | | OPENCODE_AGY_MAX_SESSIONS | Maximum concurrent ACP sessions |

Active turns do not have a default wall-clock limit. They time out only after OPENCODE_AGY_TURN_STALL_MS has elapsed since the last ACP session/update. OPENCODE_AGY_PRINT_TIMEOUT_MS covers setup RPCs and does not cut off an actively streaming turn.

Code that creates an ACP worker may set onActivity?: () => void in AcpWorkerOptions. The callback runs for each accepted ACP session/update during an active turn. It is a heartbeat signal, not a completion callback. Active turns use this idle timeout behavior rather than a wall-clock deadline, so a stream can run as long as it keeps sending updates.

Supported input

ACP text, image, and audio blocks are supported. Images and audio may be sent as base64 data URLs or local files inside the configured workspace. Remote URLs, PDFs, and video are rejected.

The provider reports native ACP image/audio input capability. Antigravity tool activity is streamed as reasoning/status content because OpenCode's ordinary provider tool loop is separate from the ACP agent tool loop.

Filesystem requests are restricted to the configured workspace. Terminal requests use sanitized environment variables and are controlled by the ACP permission policy. The adapter is not an operating-system sandbox.

Sessions and retries

The adapter forwards OpenCode message IDs and records requests before sending prompts to ACP. A repeated completed request replays the saved response. A request that failed or was interrupted after submission is rejected on retry; send a new message to continue. Clients without message IDs use a hash of the conversation and current prompt.

Session turns and metadata updates use local process locks. Another OpenCode process cannot run a turn in the same session while one is active.

OPENCODE_AGY_DATA_DIR defaults to $XDG_DATA_HOME/opencode-agy, or ~/.local/share/opencode-agy. It contains sessions.json and request receipts under requests/. Completed receipts include response events, including text, reasoning, and tool activity, up to 2 MB per request. Larger responses retain a completion marker and reject retries instead of executing again. Directories use mode 0700 and files use 0600 on POSIX filesystems. Request receipts remain after idle session metadata is pruned. Deleting them removes retry protection for those requests.

Local endpoints

• GET /health;
• GET /v1/models;
• GET /v1/usage;
• POST /v1/messages.

Requests require the loopback marker x-api-key: opencode-agy-local.

Tests

npm run check

The live test requires an authenticated official ACP server:

OPENCODE_AGY_ACP_LIVE=1 \
OPENCODE_AGY_ACP_PATH=/absolute/path/to/agy_acp_server.par \
OPENCODE_AGY_ACP_AUTH_METHOD=oauth-personal \
npm run test:live

Review Google's current terms before using subscription authentication through a third-party host.