docs: list antigravity cli as a supported flat host, with a local runtime smoke

[tkman59]

🎯 What & why

Antigravity CLI is documented as a supported flat host, the aidd-context skills know its .agents/ surfaces, and a local smoke proves a logged-in agy uses what aidd setup writes. Phase 5 of #511, stacked on #960.

🛠️ How it works

• Docs. README.md (prerequisites, compatibility row, install section), docs/FAQ.md, cli/README.md (antigravity target, flat only), docs/MAINTAINERS.md (when to run the local smoke). The README install section states the known limitation: Codex flat also writes .agents/skills/, so removing one of the two deletes skills the other uses.
• Memory. update_memory.js maps antigravity to AGENTS.md; its mirror tools.md, onboarding's detection.md and sync-arguments.md follow. Test written first, failed on unknown tool antigravity.
• Generator references (04 to 08, explore): .agents/skills/, .agents/agents/<name>/agent.md with model: inherit and a YAML tools list, .agents/rules/<slug>.md (flat, trigger frontmatter), the named-hook .agents/hooks.json shape and its cd .. && prefix. Detection uses .agents/agents/, .agents/rules/ or .agents/hooks.json: .agents/skills/ alone is no signal, Codex reads it too.
• Local smoke smoke-antigravity.sh, pnpm smoke:antigravity: setup in a throwaway repo, then evidence from logs and files, never from a turn ending.
  • Hook: interactive session under a pty with --add-dir, killed once AGENTS.md is refreshed or after 60 s.
  • Skill and /agents: print mode. An interactive initial prompt is sent as text and never expanded, which this smoke's first version tripped on.
  • Login: startup logs not logged into Antigravity before reading the stored login, so only a missing OAuth: authenticated successfully line means logged out.

🧪 How to verify

• cd cli && pnpm smoke:antigravity on a machine with agy logged in. Run on 2026-10-05, agy 1.2.17:

  PASS  hooks loaded              loaded 1 named hooks from 1 hooks.json file(s)
  PASS  memory refreshed          AGENTS.md: [aidd_docs/memory/architecture.md](aidd_docs/memory/architecture.md)
  PASS  skill expanded            expanded slash command "aidd-context-11-explore" (skill)
  PASS  agent listed              /agents: "aidd-dev-executor", aidd-dev-ghost absent
  

• Negative control: the same script with .agents/hooks.json deleted after setup fails hooks and memory, exit 1.
• Without agy on PATH: FATAL: agy not on PATH — install Antigravity CLI and log in, exit 1.
• agy reads AGENTS.md: in a repo whose only AGENTS.md names a codeword, agy -i "What is the project codeword?" answered "content":"PELICAN-4217" (transcript).
• cd cli && pnpm test: 6844 passed, 1 skipped. pnpm smoke: 144 passed, 0 failed, 1 skipped. Scripts suite: 550 passed.

⚠️ Heads-up

• Not measured, taken from Antigravity's rules docs: rule frontmatter (trigger, globs) and that only direct children of .agents/rules/ load. Commands have no Antigravity row: no docs page found.
• Correction to the plan's probe: on 1.2.17 a print-mode turn does reach the model (streamGenerateContent logged after the skill expansion). That print mode fires no hook was not re-measured.
• Still no CI runtime proof: a turn needs a Google login.

🔗 Linked issue

Refs #511

✅ I certify

• I DO CERTIFY I READ EACH LINE OF THE PULL REQUEST BECAUSE I AM A SOFTWARE ENGINEER, NOT A AI PUPPY.

🤖 Generated with Claude Code