Feature Request: Support Google / Gemini Subscription Authentication (OAuth / Code Assist)

Hi team,

Is there any plan to support subscription-based authentication (e.g., Google Account OAuth, Gemini Code Assist subscription, or web session auth) for Gemini models in Buzz / Goose, similar to how Claude subscription logins work via CLI harness?

Currently, using Gemini requires developer API keys (Google AI Studio / Vertex). Having native subscription authentication for Gemini users would make it much easier to run Gemini 3.7 / 2.5 agents without managing separate per-token billing.

Thanks for the great work on Buzz!