Add Antigravity CLI as a quorum slot (Gemini CLI deprecation) #220

Motivation

Google is deprecating the standalone Gemini CLI in favor of the Antigravity CLI (its agentic dev tool). nForma's quorum uses the Gemini CLI as a voter via the gemini-1 slot (mainTool: "gemini", display_type: "gemini-cli"). When the Gemini CLI is retired, gemini-1 will break — the Google voter needs to move to the Antigravity CLI.

Important: host-runtime support already exists, slot support does NOT

bin/install.js already treats antigravity as a host runtime — an IDE nForma installs into (config dir ~/.antigravity, MCP prefix mcp__antigravity-1__, etc.): see install.js:155,167,183,214,327-335,405,601. That is not the same as a quorum CLI slot (a subprocess voter invoked non-interactively, the role gemini-1 plays). This issue is specifically about adding Antigravity as a quorum slot / voter.

Goal

Add an Antigravity-CLI quorum slot (e.g. gemini-1 re-pointed to the Antigravity CLI, or a new antigravity-1 slot) so the Google voter survives the Gemini CLI deprecation. Keep gemini-1 working during the transition if both CLIs coexist.

Concrete integration points

The gemini-1 slot template (installed ~/.claude/nf-bin/providers.json) shows everything a CLI slot needs — mainTool, args_template (["-m", "<model>", "-p", "{prompt}"]), health_check_args (["--version"]), auth_check, oauth_rotation (creds under ~/.gemini/...), deep_probe. An Antigravity slot needs the equivalents, plus updates to the hardcoded gemini/~/.gemini references:

• Slot template — bin/providers.json / the install-time default fleet (gemini-1 entry).
• CLI detection & install — install.js:41 KNOWN_CLIS, install.js:76 install cmd (npm i -g @google/gemini-cli), install.js:400 keyword→prefix map, install.js:498 detectExternalClis; bin/nForma.cjs:2555 (@google/gemini-cli package).
• CLI resolution — bin/resolve-cli.cjs (resolves bare names like gemini; needs the Antigravity binary name).
• Auth / OAuth rotation — bin/account-manager.cjs:20-22,192,196 (creds default ~/.gemini/accounts, active ~/.gemini/oauth_creds.json) — Antigravity's credential layout.
• Hardcoded slot/model lists — update-scoreboard.cjs:70 VALID_MODELS, verify-quorum-health.cjs:41,208 SLOTS, generate-petri-net.cjs:20 QUORUM_SLOTS, token-dashboard.cjs:18 pricing, and the slot-classification CLI_COMMANDS used by /nf:mcp-status + statusline.

Open questions (need research / confirmation of the Antigravity CLI interface)

• Antigravity CLI binary name and install package (replacing @google/gemini-cli)?
• Non-interactive invocation — is there a -p/--prompt one-shot equivalent (the quorum needs print-mode, not an interactive agent loop)?
• Model selection flag (today -m gemini-3-flash-preview)?
• Health check — does --version exist?
• Auth model — does it reuse ~/.gemini credentials or a new ~/.antigravity layout? Does account/OAuth rotation still apply (and via which commands)?
• Deprecation timeline for the Gemini CLI (drives urgency / whether to keep both slots).

Acceptance criteria

• An Antigravity-CLI voter participates in /nf:quorum (responds to a non-interactive prompt, returns a verdict).
• /nf:mcp-status shows it healthy; preflight resolves its spawn target via the shared resolver (resolve-providers.cjs / resolveSpawnTarget).
• Health check + deep probe pass; OAuth rotation works (or is documented as N/A).
• No hardcoded gemini-only assumptions block the new slot (lists above updated).
• Migration path documented: what happens to existing gemini-1 installs when the Gemini CLI is removed.

Filed after the 2026-06 quorum-hardening series; the shared resolve-providers.cjs / resolveSpawnTarget plumbing from #197 should make adding the slot cleaner.