agy-sdklisted

# Antigravity SDK `google-antigravity` embeds the Antigravity harness as a Python library: it owns the agent loop, tool execution, and subagent delegation, so orchestration is expressed as configuration rather than a hand-rolled loop. The interactive CLI (`agy`) is a separate product on separate credentials — see §1. Project conventions come from [python-stack](../python-stack/SKILL.md); [google-adk](../google-adk/SKILL.md) stays the default agent framework, and this SDK is the choice when the harness itself (sandboxed tools, policies, budgets) is the value. ## 1. Install and Authenticate ```bash uv add google-antigravity # ships a ~126 MB harness binary; a git clone alone will not run export GEMINI_API_KEY="<aistudio-key>" # Gemini Developer API, pay-as-you-go with a free tier gcloud auth application-default login # Vertex path instead: LocalAgentConfig(vertex=True, project=..., location=...) ``` **Billing is the Gemini API, never the Antigravity subscription.** The SDK reads only `GEMINI_API_KEY` (or `GOOGLE_CLOUD_PROJECT` / `GOOGLE_CLOUD_LOCATION` with Vertex ADC); it never touches the OAuth login the `agy` CLI and IDE write to `~/.gemini`, so a Google AI Pro/Ultra plan grants it nothing. Without a key it fails closed at connect time with `AntigravityValidationError: A Gemini API key is required.` Keep the key in the environment or a secret manager per [sops-secrets](../sops-secrets/SKILL.md); never inline i