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>

skills/antigravity-result-handling/SKILL.md

@@ -0,0 +1,52 @@
+---
+name: antigravity-result-handling
+description: Internal guidance for presenting Antigravity (Gemini) helper output back to the user
+user-invocable: false
+---
+
+# Antigravity Result Handling
+
+This skill governs how Claude should present output that comes back from the `agy-companion.mjs` helper.
+
+## Foreground task
+
+When a foreground `task` returns:
+
+1. The stdout is the **raw Gemini response** from `agy --print`.
+2. **Return it verbatim to the user.** Do not paraphrase, summarize, restructure, or add commentary.
+3. If the response is empty or the command exited non-zero, tell the user one short sentence: *"Antigravity returned nothing — try /antigravity:status or rerun with /antigravity:setup."*
+4. If the response mentions errors that suggest agy is not authenticated, suggest running `agy login` in a terminal.
+
+## Background task
+
+When a background `task` is started, the helper prints something like:
+
+```
+[antigravity] Job started in background.
+  job id   : agy-xxxx-xxxxx
+  pid      : 12345
+  log file : /Users/.../jobs/agy-xxxx.log
+  status   : node "..." status agy-xxxx-xxxxx
+  result   : node "..." result agy-xxxx-xxxxx
+```
+
+Present this to the user as-is. Do not block on polling.
+
+## Status / result
+
+When the user runs `/antigravity:status`, the helper prints job metadata (pid, started, log path, prompt preview). When they run `/antigravity:result`, the helper streams the full log. Return it verbatim.
+
+## Streaming considerations
+
+`agy --print` in headless mode often outputs the model's tokens as they arrive. The companion script streams them to stdout. Do not hold the output until the end — Claude can present it as it streams.
+
+## Length
+
+Antigravity responses can be long. Do not truncate or summarize unless the user explicitly asks for a summary. If the response is very long, mention at the end: *"(Antigravity response was N lines)"*.
+
+## Errors
+
+If the helper exits with a non-zero code:
+- Exit code 124 = timeout. Tell the user the prompt timed out and suggest `--timeout 20m` or `--background`.
+- Exit code 2 = invalid args. Show the user what was wrong.
+- Other = unknown error. Pass through the stderr.