feat: add Antigravity CLI plugin.json and mcp_config.json

[patrickcping]

Adds the required plugin marker and optional MCP server config for Antigravity CLI compatibility under plugins/ping-identity/.

Changes

• plugins/ping-identity/plugin.json — required package marker for Antigravity CLI
• plugins/ping-identity/mcp_config.json — optional MCP server config declaring aic and davinci servers via local npx processes

Validation

Installed directly from this PR branch and validated via agy:

$ agy plugin install https://github.com/pingidentity/agent-plugins/tree/feat/antigravity-plugin-config/plugins/ping-identity

Cloning plugin from https://github.com/pingidentity/agent-plugins.git...
  [ok]  ping-identity
        ✔ skills     : 6 processed
        - agents     : skipped (not found)
        - commands   : skipped (not found)
        ✔ mcpServers : 2 processed
        - hooks      : skipped (not found)

6 skills and 2 MCP servers loaded successfully.

[patrickcping]

It looks like this would lead to the plugin install URL being https://github.com/pingidentity/agent-plugins/tree/main/plugins/ping-identity (agy plugin install https://github.com/pingidentity/agent-plugins/tree/main/plugins/ping-identity) because there doesn't appear to be any custom marketplace support yet

[george-bafaloukas-forgerock]

Thanks for getting the Antigravity config in, Patrick — nice and tight, and appreciate the agy validation output in the description. One thing I'd love you to confirm before this goes in:

Substitution model (the main question). mcp_config.json uses Claude Code's ${user_config.*} placeholder syntax, but the new plugin.json doesn't declare a userConfig block (the Claude variant resolves those only because .claude-plugin/plugin.json carries the full userConfig schema). The Cursor variant sidesteps this entirely by reading ${env:...}. So as written I don't think the MCP env injection will actually resolve under Antigravity — the placeholders would come through empty. Could you confirm how agy does config substitution? Two ways to land it:

• If Antigravity supports user_config substitution → add the userConfig block to this plugin.json (copy the 5 fields from .claude-plugin/plugin.json).
• If it doesn't → switch to ${env:...} like cursor-mcp.json.

The agy install log shows the servers loading, but that wouldn't catch empty env values at runtime, so worth a quick check against a real DaVinci tenant. Left a couple of minor inline notes too — nothing blocking beyond the substitution question. 🙏

[george-bafaloukas-forgerock]

Minor: the davinci server here only passes DAVINCI_MCP_ENVIRONMENT_ID, whereas both claude-mcp.json and cursor-mcp.json also pass AUTHORIZATION_CODE_CLIENT_ID, ROOT_DOMAIN, and CUSTOM_DOMAIN. Without the client ID + domain, the DaVinci server won't authenticate / will default the region for any non-standard tenant. Looks like an accidental trim (the aic block matches the others exactly) — suggest copying the full 4-var env from claude-mcp.json:

"env": {
  "DAVINCI_MCP_ENVIRONMENT_ID": "${user_config.davinci_environment_id}",
  "AUTHORIZATION_CODE_CLIENT_ID": "${user_config.davinci_client_id}",
  "ROOT_DOMAIN": "${user_config.davinci_root_domain}",
  "CUSTOM_DOMAIN": "${user_config.davinci_custom_domain}"
}

(env-var names if you go the ${env:...} route instead.)

[george-bafaloukas-forgerock]

Minor/consistency: this declares "name": "ping-identity", while .claude-plugin and .cursor-plugin both use "ping-identity-agent-plugins". If Antigravity keys off the directory name this is fine — but if the plugin identifier matters for how it's referenced/configured, worth aligning with the other two variants for consistency.