Initial commit — Antigravity plugin v0.1.0

Plugin Claude Code miroir du plugin codex officiel d'OpenAI, mais
pour Google Antigravity (agy CLI). Headless via:

  agy --print --dangerously-skip-permissions --print-timeout 10m

Includes:
- 1 forwarder agent (antigravity-rescue)
- 5 slash commands (setup, rescue, status, result, cancel)
- 3 internal skills (cli-runtime, result-handling, gemini-prompting)
- agy-companion.mjs runtime (task / setup / status / result / cancel)
- marketplace.json for `/plugin marketplace add`

Tested: setup OK, foreground task OK, background workflow OK
(except OAuth refresh which requires interactive TTY).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

commands/setup.md

@@ -0,0 +1,39 @@
+---
+description: Check whether the local Antigravity (agy) CLI is ready
+allowed-tools: Bash(node:*), Bash(curl:*), Bash(bash:*), AskUserQuestion
+---
+
+Run:
+
+```bash
+node "${CLAUDE_PLUGIN_ROOT}/scripts/agy-companion.mjs" setup --json
+```
+
+Parse the JSON output.
+
+If `installed` is `false`:
+- Use `AskUserQuestion` exactly once to ask whether Claude should install Antigravity now.
+- Put the install option first and suffix it with `(Recommended)`.
+- Use these two options:
+  - `Install Antigravity (Recommended)`
+  - `Skip for now`
+- If the user chooses install, run:
+
+```bash
+curl -fsSL https://antigravity.google/cli/install.sh | bash
+```
+
+- Then rerun:
+
+```bash
+node "${CLAUDE_PLUGIN_ROOT}/scripts/agy-companion.mjs" setup --json
+```
+
+If `installed` is already `true`:
+- Do not ask about installation.
+
+Output rules:
+- Present the final setup output to the user in a human-readable summary.
+- If the install was skipped, present the original setup output.
+- Mention the headless invocation command (`headless_mode`) so the user knows what's under the hood.
+- If installation succeeded but agy is not yet authenticated, instruct the user to run `agy` once interactively in a terminal to complete Google sign-in.