Document marketplace distribution and Copilot Customize path

[Niels Laute (niels9001)]

Summary

• Add a public marketplace-distribution specification for GitHub Copilot, Claude Code, Cursor, and OpenAI.
• Explain how the GitHub Copilot app's new Customize tab discovers plugins from configured marketplaces and why updating the existing Awesome Copilot record is the path to appearing there.
• Separate compatibility, direct installation, public listing, and featured placement so the repository does not overstate distribution status.
• Define the shared release gate, package source for each client, submission/update process, validation steps, artwork requirements, and unresolved eligibility risks.
• Link the specification from the README and track execution in Track Agent Plugins 1.0 packaging and marketplace distribution #158.

Why

Agent Plugins 1.0 makes the skills portable, but it does not publish them to vendor catalogs. Each vendor has a different intake and update model:

• GitHub Customize reads configured plugin marketplaces; winui already has an Awesome Copilot entry that must be updated to the new package path and immutable release.
• Claude accepts public Git repository submissions through Anthropic's directory forms.
• Cursor manually reviews every version and currently documents a no-binaries policy that blocks the canonical package.
• OpenAI uses one universal Plugins Directory for Codex and ChatGPT and requires a generated review-safe skills bundle plus product/security guidance for local Windows execution.

The specification links directly to the official vendor documentation and marks undocumented behavior as unknown rather than guessing.

Validation

• Verified every local Markdown link resolves.
• Checked every external URL in the specification; public documentation links return successfully and authenticated submission portals return the expected access-controlled response.
• Reviewed the document against the repository's current staging package layout and release policy.

Documentation-only change; no changelog entry is required by CONTRIBUTING.md.

Preview

Read the rendered marketplace distribution specification.

[Jaylyn Barbee (Jaylyn-Barbee)]

Some notes and things I found, sorry if I repeated anything already in the doc.

[Jaylyn Barbee (Jaylyn-Barbee)]

We need to make sure that right now on awesome-copilot that our plugin is resolving. https://github.com/github/awesome-copilot/blob/c956566a35c3c2e635f019e7a1bfa59d9497e8b1/plugins/external.json#L1308 referencing "path": "plugins/winui" not plugins/winui/agent-plugin

in the future we should pin to a release branch like you're saying so that changes in this repo don't impact the general relase.

[Jaylyn Barbee (Jaylyn-Barbee)]

Wanted to comment on the update behavior for GH CP CLI and App

The suggested flow to add an external plugin outlines opening an issue with certain information so that it gets tagged with the right labels to get pulled in to the right workflows (ie staleness checks). win-dev-skills external plugin was added directly via PR so exists outside of this system.