Codex install command fails with "invalid marketplace file" #408

Summary

The Codex install command shown in the README does not work with the current Codex CLI.

README currently suggests:

codex plugin marketplace add heygen-com/hyperframes --sparse .codex-plugin --sparse skills --sparse assets

Running that against heygen-com/hyperframes fails even though the repository contains .codex-plugin/plugin.json.

Steps to reproduce

1. Install/update Codex CLI.
2. Run:

   codex plugin marketplace add heygen-com/hyperframes --sparse .codex-plugin --sparse skills --sparse assets

Actual result

Codex exits with:

Error: invalid marketplace file `/Users/.../.codex/.tmp/marketplaces/.staging/...`: marketplace root does not contain a supported manifest

Expected result

Either:

• the plugin installs successfully using the documented command, or
• the README uses the correct installation flow for the current Codex CLI.

Notes

• Tested with codex-cli 0.122.0.
• The repo does contain a plugin manifest at .codex-plugin/plugin.json:
  https://github.com/heygen-com/hyperframes/blob/main/.codex-plugin/plugin.json
• This looks like a mismatch between:
  • a repository that exposes a Codex plugin via .codex-plugin/plugin.json, and
  • codex plugin marketplace add, which appears to expect a marketplace root manifest rather than a single plugin repo.

If that command is no longer valid for current Codex versions, updating the README with the supported install path would likely fix the confusion.