test(cli): prove sync restores only what antigravity setup wrote

[tkman59]

🎯 What & why

Proves the last open criterion of #511: restore (aidd sync) touches only what Antigravity setup wrote. Stacked on #961.

🛠️ How it works

• antigravity-foreign-files.e2e.test.ts gains a sync --force case: setup aidd-context, add a user named hook lint to .agents/hooks.json and a user skill, drift an AIDD skill, sync.
  • The AIDD skill is restored byte for byte.
  • The user skill is untouched.
  • .agents/hooks.json keeps lint and aidd-context with the same content. The test compares parsed JSON, not bytes: restore unmerges then remerges its own key, so aidd-context moves after lint.
• The existing clean case moves into the same file, renamed clean-antigravity-foreign-file → antigravity-foreign-files to cover both.

🧪 How to verify

• cd cli && npx vitest run --project e2e tests/e2e/antigravity-foreign-files.e2e.test.ts: 2 passed.
• Mutation: making withoutPlugin in antigravity-hooks.ts return {} fails the sync case on the missing lint key; the clean case still passes.
• pnpm test: 6845 passed, 1 skipped. pnpm smoke: 144 passed, 0 failed, 1 skipped.

⚠️ Heads-up

The test passed on first run: it characterises existing behaviour, it does not drive a fix. Found while writing it, not fixed here (shared project-hooks route, not Antigravity-specific code):

• A drifted hook script, or an edited AIDD entry in .agents/hooks.json, makes sync --force refuse (hook script '.agents/hooks/aidd-context/update_memory.js' was edited after install; detach refused) and exit 1 having restored nothing, including unrelated drifted skills.
• Cursor does not detect the same script drift at all: Nothing to restore — all files are unmodified.

🔗 Linked issue

Closes #511

✅ I certify

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

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