ADR-0185 - Cursor and Antigravity setup targets

Context

ADR-0175 named Codex, Claude Code, Kimi Code, ZCode, and OpenCode as explicit setup targets. Cursor and Antigravity now have documented user-level instruction files [CURSORRULES] [ANTIGRAVITYRULES].

Decision

1. Add two identifiers. suspec setup accepts cursor and antigravity beside the existing explicit harness names.
2. Cursor uses the documented file-backed user-rule directory. Setup writes ~/.cursor/rules/AGENTS.md. It requires ~/.cursor. If ~/.cursor/rules is missing, install creates that one leaf directory. If the path exists and is not a safe directory, setup stops. Account-synced Settings User Rules stay unobservable and do not redirect installation.
3. Antigravity uses the documented global rules file. Setup writes ~/.gemini/GEMINI.md. It does not chase AGENTS.md, Antigravity subdirectories, or workspace .agents/rules.
4. Keep the rest of setup unchanged. Check, preview, --yes, reversal, envelope version, and the absent MCP surface do not change.

Narrowed decisions

• ADR-0174: ordinary native files remain the targets; Cursor and Antigravity now have named files.
• ADR-0175: the explicit target set grows by those two names.

Consequences

• Cursor and Antigravity receive the same policy bytes as the other harnesses.
• Gemini CLI shares ~/.gemini/GEMINI.md; setup reports that fact and still uses the documented Antigravity file.

Status

Accepted (2026-08-17). Narrows ADR-0174 and ADR-0175.