[steve-calvert-glean]

Problem

The codex target builds an Agent Plugins package with one client profile and one marketplace, and the agent-plugins target builds packages with none. Codex, GitHub Copilot, VS Code and Cursor all read Agent Plugins packages, so a plugin built once could serve all of them. pluginpack had no way to write more than one client's marketplace and client-only files for the same package.

Change

Adds clients to the agent-plugins target (ADR 0002):

"agent-plugins": {
  outDir: "dist/agent-plugins",
  clients: { codex: {}, copilot: {} },
  plugins: {
    acme: {
      source: "shared/acme",
      manifest: { extensions: { "com.openai": { interface: { displayName: "Acme" } } } },
      clients: { codex: { entry: { policy: { installation: "AVAILABLE", authentication: "ON_INSTALL" }, category: "Productivity" } } },
    },
  },
},

• Each plugin is built once: plugin.json, mcp.json, skills/.
• Each listed client gets its marketplace: Codex .agents/plugins/marketplace.json, Copilot .github/plugin/marketplace.json.
• Client-only kinds a listed client loads go in its extension directory. Copilot agents go to com.github.copilot/agents/NAME.agent.md, renamed from NAME.md.
• validate checks every package, then each client marketplace that's present. Every entry must point at a package with the same plugin.json name, and Copilot agents need a valid name and frontmatter.
• Without clients, the target still writes packages only. One config change applies with or without clients: the target-level manifest and per-plugin entry are now config errors, because the target writes no shared marketplace. Move them to clients.<client>.manifest and plugins.<name>.clients.<client>.entry. Before, they were accepted and ignored. agent-plugins is unreleased (it landed after v0.11.1), so no released config breaks. Other targets don't change: Glean's claude, cursor and codex output is byte-identical to main (191 files).

Layout facts for each client are cited in src/package-clients.ts (Copilot CLI plugin reference, retrieved 2026-10-20) and CONFORMANCE.md.

Verification

• npm run check passes with 292 tests on Node 24, and CI runs it on the 22.12.0 floor.
• Tests cover the build, the config errors, the validate errors, and a conformance test against the vendored Agent Plugins schemas.
• End to end with the Glean plugin: Copilot CLI 1.0.100 installs it from the generated marketplace (glean@glean-plugins, 19 skills, MCP server registered), and Codex 0.160.1 installs the same package from its marketplace.

Known gaps

• install-info still reports no install command for agent-plugins. It will be updated when the Copilot plugin publishes.
• Copilot loading the agents in a signed-in session is untested.