fix: declare antigravity-cli Stop hook in the flat form agy accepts

[rubenmarcus]

Fixes #1206

What / Why / How

agy rejects the whole plugin hooks.json when Stop carries the grouped matcher/hooks wrapper, so no context-mode hook ever runs under agy. The filer's log line: failed to parse hooks for plugin ...: invalid hook "hooks": command hook must specify 'command', reproduced on agy 1.2.11. agy's bundled docs table groups only PreToolUse/PostToolUse; Stop must be a flat list of handler objects.

Three changes, exactly the files #1206 enumerates:

• configs/antigravity-cli/hooks.json and configs/antigravity-cli/hooks/hooks.json: Stop is now [{ "type": "command", "command": "context-mode hook antigravity-cli stop" }], no wrapper. PreToolUse/PostToolUse stay grouped.
• src/adapters/antigravity-cli/index.ts: desiredStop is written flat, so context-mode upgrade repairs existing installs (a legacy grouped Stop is filtered out and replaced, same command). hookEntryHasCommand now also accepts a handler object whose command matches directly, so ctx_doctor recognizes the flat form in both profiles.
• tests/adapters/antigravity.test.ts: the grouped-form assertions moved to the flat contract, plus a rewrite test that feeds a legacy grouped Stop through configureAllHooks, and a plugin-profile validateHooks case that must report best-effort Stop hook also configured.

Affected platforms

• Claude Code
• Cursor
• VS Code Copilot (GitHub Copilot)
• JetBrains Copilot
• Gemini CLI
• Qwen Code
• OpenCode
• KiloCode
• Codex CLI
• OpenClaw (Pi Agent)
• Pi
• Kiro
• Antigravity
• Zed
• All platforms

Test plan

# next (4621364), new assertions first
Tests  5 failed | 32 passed   # tests/adapters/antigravity.test.ts

# this branch (a8b8261)
Tests  37 passed (37)         # tests/adapters/antigravity.test.ts

tests/hooks/antigravity-cli-hooks.test.ts (runtime dispatch) is 5 failed / 6 passed on this machine, identical on pristine next: no session DB created in the spawned hook process, the failures predate this change. No path handling touched, so no Windows-path risk.

Checklist

• Tests added/updated (TDD: red → green)
• npm test passes (touched suite green; environmental failures identical on base, see test plan)
• npm run typecheck passes
• Docs updated if needed (README, platform-support.md)
• No Windows path regressions (forward slashes only)
• Targets next branch (unless hotfix)

Prepared with AI assistance (GLM 5.3 via Oh My Pi) and reviewed before submission.