Decide how to handle Gemini CLI support

[saitota]

Background

Google announced that Gemini CLI is transitioning to Antigravity CLI:
https://developers.googleblog.com/an-important-update-transitioning-gemini-cli-to-antigravity-cli/

The post says consumer Gemini CLI access will stop serving requests on June 18, 2026. It also says Antigravity CLI will carry over key Gemini CLI concepts such as Agent Skills, Hooks, Subagents, and Extensions, though not with full 1:1 parity at launch.

Concern

Rulesync currently supports both geminicli and antigravity.

Given the upstream transition, we may need to think about how this affects the existing Gemini CLI support in Rulesync.

Discussion Points

• How should geminicli be treated going forward?
• Should antigravity become the recommended target for new Google CLI users?
• Can any existing Gemini CLI implementation be reused if Antigravity CLI keeps compatible concepts?
• How should Gemini CLI Extensions and Antigravity plugins be handled, if Rulesync supports them?
• Should README/docs mention this upstream transition?