Antigravity Marketplace plugin¶

Goal¶

List Superpowers in the Google Antigravity plugin Marketplace, as part of a partnership with Google. That requires a native Antigravity plugin manifest with the Marketplace presentation fields, a logo, and a session bootstrap that works on the native plugin path.

Source: "Antigravity Plugin Marketplace Publishing Guide" (PDF from Google), plus probes against agy 1.3.1 recorded below.

Current state (agy 1.3.1)¶

• agy plugin install https://github.com/obra/superpowers succeeds, but only through agy's Gemini-extension fallback: agy plugin list reports "source": "gemini-cli". The bootstrap rides GEMINI.md's @ lines, which the model treats as hints and follows with view_file. The acceptance test passes on this path.
• agy copies our Claude-format hooks/hooks.json to the install root as hooks.json and fails to parse it on every session: invalid hook "hooks": command hook must specify 'command'.
• agy plugin validate . on the repo fails: missing plugin.json.

Probe findings (agy 1.3.1)¶

Each probe installed a throwaway plugin, ran agy -p, and uninstalled it.

1. agy's hook events are PreToolUse, PostToolUse, PreInvocation, PostInvocation, and Stop. There is no SessionStart. agy's embedded docs use named top-level hooks ({"<name>": {"PreToolUse": [...]}}), which differs from the PDF's {"hooks": {...}} example.
2. rules/AGENTS.md in a plugin loads as an always-on rule on every session.
3. In a rule, an @ path relative to the rule file is rewritten to an absolute install path (@../skills/x/SKILL.md becomes @/Users/<u>/.gemini/config/plugins/<plugin>/skills/x/SKILL.md). Its content is not inlined. ${PLUGIN_ROOT} is not substituted in rules. A path that does not resolve relative to the rule file is left as written.
4. With .antigravity-plugin/plugin.json present, agy installs the plugin as "source": "antigravity", finds all 15 skills, and skips hooks (no root hooks.json), so the parse warning goes away.
5. A staged copy of the repo with the native manifest and a one-line rules/AGENTS.md (@../skills/using-superpowers/SKILL.md) passed the acceptance test: the model read using-superpowers, then antigravity-tools.md, then brainstorming, and replied "Using superpowers:brainstorming…" with a clarifying question. No code.
6. The repo-root AGENTS.md (contributor guidelines) is copied into the install but is not loaded as a rule. Only rules/AGENTS.md is.

Design¶

1. Native manifest: .antigravity-plugin/plugin.json¶

The guide allows the manifest at .antigravity-plugin/plugin.json, which matches our other harness dotdirs. Fields:

No skills or mcpServers fields: the defaults (skills/, no MCP config) are what we want, and probe 4 confirmed default discovery finds all skills.

2. Bootstrap: skill discovery, no extra files¶

agy lists each installed skill's description, and using-superpowers' "Use when starting any conversation" gets the model to load it. The plugin ships no rules/ and no hooks.json.

This replaced a first design, a one-line rules/AGENTS.md pointer, after the final review found that Cursor also loads any rules/*.md a plugin ships from the same repo root. Alternatives probed on agy 1.3.1 and rejected:

• A PreInvocation hook. It runs before every model call and hooks.json must sit at the plugin root. An ephemeralMessage is dropped on the next call; a userMessage persists, and gating it on invocationNum == 0 and initialNumSteps == 1 injects exactly once per conversation, but agy still starts the hook process on every call.
• No manifest field relocates hooks.json or rules/.

Verified with no bootstrap file, 12/12 runs: "Let's make a react todo list" (3) and "add a settings page" (3) load brainstorming before any code; "this test is failing, can you fix it?" (3) loads systematic-debugging before any edit; a react-todo second turn after an unrelated first turn (3) loads brainstorming. Model: Gemini 3.8 Flash. The risk is that triggering depends on the model honoring a skill description; the once-per-conversation hook is the fallback if it slips.

3. Logo: assets/antigravity-logo.png¶

512×512 PNG, transparent background. A white rounded square (inset 31px, corner radius 100) holds the assets/superpowers-small.svg mark in #1a1a1a, scaled to about 70% of the square's width and centered. No border; on a light theme it reads as a bare mark on white, which is acceptable.

scripts/render-antigravity-logo.sh composes the SVG from superpowers-small.svg and rasterizes it with rsvg-convert. It is the only way the PNG gets regenerated; it has help text and fails clearly when rsvg-convert is missing.

4. Version bumps¶

Add { "path": ".antigravity-plugin/plugin.json", "field": "version" } to .version-bump.json.

5. Codex sync¶

Add /.antigravity-plugin/ and /assets/antigravity-logo.png to EXCLUDES in scripts/sync-to-codex-plugin.sh, and cover them in tests/codex-plugin-sync/test-sync-to-codex-plugin.sh.

6. README¶

The Antigravity install command stays agy plugin install https://github.com/obra/superpowers. The prose changes from "runs the plugin's session-start hook" to describing skill discovery. Add the Marketplace route once it exists; until then, no claim about it.

7. Tests: tests/antigravity/¶

• test-plugin-manifest.sh (CI-safe, mirrors tests/kimi/test-plugin-manifest.sh):
• manifest parses; name matches the kebab-case pattern and equals superpowers;
• every Marketplace-required field is present and non-empty: name, description, displayName, logo, suggestedPrompts (1–3 non-empty strings), version, author;
• description is at most 160 characters;
• version equals .claude-plugin/plugin.json's version;
• logo file exists, is a PNG, and is square and at least 128×128;
• .version-bump.json lists the manifest;
• using-superpowers' description still says "Use when starting any conversation", which the bootstrap relies on;
• no root plugin.json, hooks.json, or rules/ exists.
• When agy is on PATH, also run agy plugin validate on the repo and require [ok] with skills processed.
• Update the header comment of test-antigravity-tools.sh, which still says agy runs the SessionStart hook.

Live acceptance (not in CI): install the branch's tree into agy, run "Let's make a react todo list" at least three times in clean workspaces, and require that brainstorming triggers before any code each time. Uninstall afterward.

8. Porting guide: separate commit¶

docs/porting-to-a-new-harness.md describes .antigravity-plugin/install.sh and a generated ANTIGRAVITY.md that do not exist. Fix it in its own commit:

• Routing table row: Antigravity uses the surfaced skill index.
• The "no Skill tool" section: replace the contextFileName advice for Antigravity with the skill-index bootstrap, and record the hook and rule findings (no session-start event, PreInvocation per call, no ${PLUGIN_ROOT} in hooks, shared plugin roots leak rules/ into Cursor).
• The distribution table: Antigravity installs from a git URL (agy plugin install <url>) and lists in its Marketplace.
• The installer-stripping section: drop the install.sh / ANTIGRAVITY.md example.
• The harness index table has no Antigravity row; add one (manifest, bootstrap, tool mapping, tests, install).

Out of scope¶

• Marketplace submission mechanics. The guide does not describe how to submit; that goes through Jesse's Google contact.
• Antigravity 2.0 and the IDE. Not installed here, so not verified. The README makes no claims about them.
• Open PR #2350, which copies using-superpowers into a generated rule. Jesse decides how to respond after this lands; I draft the reply.
• .hermes-plugin/ and .muse-plugin/ are missing from the Codex sync excludes. Unrelated; noted for a separate fix.