Retire Gemini CLI as a builder harness

[mohidmakhdoomi]

Problem

Codev still treats the standalone Gemini CLI as a supported builder harness. Google retired Gemini CLI availability for Pro, Ultra, and free tiers on June 18, 2026, so this option is no longer available to most users and should not remain presented as supported.

Scope

Retire the standalone Gemini CLI as a Codev builder option and ensure users receive clear, accurate guidance that it is no longer supported.

Non-goals

• Adding Antigravity CLI (agy) as a builder
• Changing the existing agy consultation lane
• Changing or expanding agy architect support

No existing issue currently covers agy builder support. That would require a separate issue if desired; this issue is limited to retiring the unavailable Gemini CLI builder.

Acceptance criteria

• Gemini CLI is no longer presented or treated as a supported builder option.
• Users selecting Gemini CLI as a builder receive a clear explanation that the option has been retired.
• Existing Claude, Codex, OpenCode, and custom builder support remains unaffected.

Related issues

• Gemini CLI > Antigravity CLI - June 18, 2026 DEADLINE #778 — Gemini CLI retirement and migration of the consultation lane to agy
• Support agy (Antigravity CLI) as an architect #1063 — possible agy architect support; does not cover builder support