Feature Request: Add Google Antigravity as a First-Class gstack Host

Please add Google Antigravity as a first-class supported host in gstack.

Antigravity has a native Agent Skills and Workflows system using:

.agents/skills//SKILL.md
.agents/workflows/*.md

Currently, there does not appear to be a current upstream gstack host configuration for Antigravity. This forces users to rely on older third-party ports/forks that can fall behind the rapidly changing upstream gstack project.

Why this matters

gstack is evolving quickly, with new skills and improvements landing frequently. An older Antigravity-specific fork requires users to manually keep a separate port synchronized with upstream.

A first-class Antigravity host would allow Antigravity users to receive the same current gstack skills and improvements as other supported hosts without depending on an unofficial fork.

Proposed implementation

The current gstack architecture already makes this relatively straightforward.

Add:

text
hosts/antigravity.ts

using the existing defineHost() mechanism, then register it in:

text
hosts/index.ts

The Antigravity host should generate skills into:

text
.agents/skills/

for project-local installs. This path is confirmed by Antigravity's own docs.

The global/user-level path is intentionally left open in the example below rather than guessed at. Antigravity currently has three flavors (Antigravity IDE, Antigravity CLI, and the Antigravity 2.0 agent manager), and independent testing as of mid-2026 has found the documented global skill location to be inconsistent across them and not fully reliable in practice. I'd rather this be verified against a real install than hard-coded from docs that may be stale — happy to help test and pin down the actual behavior before this field is filled in.

The host configuration should translate gstack's Claude-specific paths/references into Antigravity's conventions, similar to the existing host adapters (per the pattern used for Cursor/Kiro/OpenCode: mostly path rewrites and tool renames).

Example host shape

Conceptually (see scripts/host-config.ts for the full HostConfig interface — this omits several real fields like cliAliases, hostSubdir, usesEnvVars, frontmatter, and generation):

ts
import { defineHost } from './define-host';

const antigravity = defineHost({
name: 'antigravity',
displayName: 'Google Antigravity',

// Antigravity CLI
cliCommand: 'agy',

// Native Antigravity project skills location (confirmed via docs)
localSkillRoot: '.agents/skills/gstack',

// Global/user-level root: needs verification against a real
// Antigravity install before pinning this down (see note above)
// globalRoot: '...',

extraPathRewrites: [
{
from: 'CLAUDE.md',
to: 'AGENTS.md',
},
],
});

export default antigravity;

The exact paths and tool rewrites should follow Antigravity's current documented and tested skill/workflow behavior rather than an older third-party port.

Important distinction from issue #1625

This request is not asking for /agy as a peer-review tool.

Issue #1625 proposes:

text
gstack
└── /agy
└── calls Antigravity CLI

This issue proposes the reverse host integration:

text
Google Antigravity
└── runs current gstack skills
└── generated from upstream gstack

In other words, Antigravity should be able to use gstack natively rather than gstack merely being able to invoke agy.

Desired behavior

After installation, an Antigravity project should be able to discover the current gstack skills through .agents/skills/ and use them without requiring a stale third-party fork.

For example:

text
.agents/
├── skills/
│ ├── gstack-office-hours/
│ ├── gstack-plan-ceo-review/
│ ├── gstack-plan-eng-review/
│ ├── gstack-review/
│ ├── gstack-qa/
│ └── ...
└── workflows/

The generated skills should be kept in sync with upstream gstack through the existing generator/host system.

Benefits
No stale third-party fork required
Automatic access to new gstack skills
Uses Antigravity's native Agent Skills architecture
Consistent gstack behavior across supported hosts
Much easier maintenance than maintaining an independent Antigravity port
Suggested acceptance criteria
Add hosts/antigravity.ts
Register Antigravity in hosts/index.ts
Generate valid Antigravity SKILL.md files
Ensure generated files contain no inappropriate Claude-specific paths
Support project-local .agents/skills/
Verify actual global/user-level skill path against a real Antigravity install (IDE, CLI, and agent manager) before hard-coding globalRoot
Support Antigravity CLI detection where appropriate
Add tests for the host configuration and generated output
Document Antigravity installation and usage
Verify compatibility with current Antigravity Agent Skills behavior
Existing related issue

This should be considered complementary to #1625 (/agy), not a replacement for it.

#1625 is about gstack invoking Antigravity as an external peer agent.

This issue is about Antigravity being able to run current gstack as a native host.

That distinction is important because users want both directions of interoperability.

References
Google Antigravity Agent Skills / Workflows docs (antigravity.google/docs/skills)
gstack ADDING_A_HOST.md
Existing gstack issue #1625: /agy peer-agent integration

I would be happy to help test the Antigravity host implementation, including nailing down the global skill path across Antigravity's IDE/CLI/agent-manager flavors before that part is finalized.

Read scripts/host-config.ts and the existing host adapters, then inspect hosts/index.ts and ADDING_A_HOST.md before creating hosts/antigravity.ts. Done means the host is registered, generates valid project-local .agents/skills/ files without inappropriate Claude-specific paths, supports appropriate CLI detection, includes configuration/output tests, documents installation, and verifies the global path across Antigravity variants.

Written by the indexing model from the issue text.