bb-plugin-google-antigravity-acp

Google Antigravity as a first-class bb agent provider through Antigravity's official ACP server (agy_acp_server.par).

Registers the acp-antigravity provider (family acp), exactly like bb's builtin ACP agents:

• server.ts — bb.providers.register with the launch spec in experimental_bridgeOptions.acpLaunchSpec; plugin settings for install paths; the bb google-antigravity-acp status and bb google-antigravity-acp install commands.
• host.ts — re-exports the canonical ACP provider bridge (@get-bb/plugin-sdk/provider-bridge/acp, the same bridge the builtin provider-acp plugin uses) and implements the host RPC the install/status commands call, so installs run on the target machine, not on the bb server.
• install.ts — shared install logic: resolves the official distribution from the ACP registry (pinned to a commit SHA), downloads, safely extracts, and links the server binary, usage proxy wrapper, and sandbox helper onto PATH (no environment variables needed).
• icons/google-antigravity.svg — provider mark (path-shaped, theme-tinted).

Install the plugin

bb plugin install git:github.com/rawizhere/bb-plugin-antigravity-acp --yes

For development, install from a checkout instead:

bb plugin install .                  # from this directory
bb plugin reload google-antigravity-acp

Settings

Setting	Default	Purpose
installDir	~/.local/opt/agy-acp-server	Where the downloaded server binaries are extracted. ~ expands per machine.
binDir	~/.local/bin	Where the server binary and sandbox helper are linked; must be on the machine's PATH.
defaultModel	(empty — latest Flash)	Default model family for new threads, e.g. gemini-3.8-flash or gemini-3.1-pro.
defaultReasoningEffort	(empty — model default)	Preferred effort variant for the default model: low, medium, or high.

Install the server binary

bb google-antigravity-acp install

The command runs on the machine that will launch the agent (the current thread's host, or --machine <id-or-name> to pick another enrolled machine):

• detects the platform/arch and takes the official zip URL for it from the ACP registry (agentclientprotocol/registry → antigravity-acp, pinned to REGISTRY_COMMIT in install.ts), falling back to a pinned copy embedded in the plugin;
• downloads and extracts into ~/.local/opt/agy-acp-server (configurable via --install-dir, or the installDir plugin setting). Extraction never uses tar (bsdtar does not sanitize ../ zip entries); it uses unzip or a validated python3 zipfile extraction, and PowerShell's Expand-Archive on Windows;
• symlinks the raw binary agy_acp_server_raw.par and sandbox helper localharness_external into ~/.local/bin (configurable via --bin-dir / binDir), and installs the lightweight ACP context usage proxy wrapper as agy_acp_server.par; on Windows it copies them and only appends the dir to the user PATH when you pass --update-path (setx permanently edits HKCU\Environment — opt in explicitly, and be aware of its 1024-character truncation limit);
• makes the binaries executable and records the install in a manifest.

Install once per machine that should run Antigravity threads. The provider only appears on a machine where the health probe finds agy_acp_server.par on PATH; the ACP server finds the sandbox helper on PATH too (the install links both into binDir), so no per-machine environment variables are needed.

bb google-antigravity-acp install --machine macbook        # this machine

The machine's daemon shell must have binDir on PATH. The command warns when it is not; pick a dir that is (e.g. /usr/local/bin) with --bin-dir.

Useful flags:

bb google-antigravity-acp install --machine macbook        # install on a specific machine
bb google-antigravity-acp install --force                  # re-download even if already installed
bb google-antigravity-acp install --from ./agy-acp.zip     # explicit source (URL or local file)
bb google-antigravity-acp install --update-path            # also append binDir to the user PATH (Windows)
bb google-antigravity-acp install --json                   # machine-readable output

~/.local/bin must be on the machine's PATH for the provider health probe to find the server. The command warns when it is not.

Verify

bb google-antigravity-acp status        # where the server is, per machine
bb provider list                        # acp-antigravity appears (visibility: installed)
bb provider models acp-antigravity
bb thread spawn --provider acp-antigravity --prompt 'hi'

Model and reasoning selection

Antigravity exposes effort variants as separate models (... Low, ... Medium, and ... High). Select the desired variant in the model picker. BB reasoning remains Medium because Antigravity's ACP server manages it internally; Fast mode is unavailable.

Context window usage reporting

Google's official agy_acp_server.par tracks exact token usage inside its local conversation database (~/.gemini/antigravity-acp/conversations/<sessionId>.db), but omits emitting usage_update over the ACP stdio bridge.

The POSIX install renders a lightweight transparent proxy wrapper as agy_acp_server.par, pinning the verified Node interpreter and installed real-binary path while keeping the official raw binary intact (agy_acp_server_raw.par). Installation verifies an ACP initialize handshake before succeeding. Windows currently runs the raw binary without context usage injection. The POSIX wrapper reads token usage metadata in real time from the session database and injects standard ACP session/update (usage_update) events with used and size before turn completion.

This enables BB's native context window tracking and context meter plugins (such as context-meter) to display live token usage for Antigravity threads.

Security notes

• The ACP registry is fetched from a pinned commit (REGISTRY_COMMIT), never from an unpinned branch, so a registry compromise cannot inject an arbitrary binary onto PATH.
• The download source is explicit: the pinned registry URL, or an explicit --from flag. There is no environment-variable redirect.
• Extraction validates archive entries and refuses ..//absolute paths.
• No code from this plugin executes the downloaded file except impossible — the server binary itself (agy_acp_server.par), which is Google's official release, is what the provider runs.

Auth

Auth is handled in-band by the ACP server (Google account OAuth, Gemini API key, Agent Platform). First run surfaces a login flow in the thread. State lives under ~/.gemini/antigravity-acp/settings.json.