[BUG] --plugin-dir: Marketplace 'inline' not found in configuration

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

I have a plugin I've developed. I want to test using it in a another repo before I publish it to our private marketplace. So I start it like this:
claude --plugin-dir=/path/to/my-plugin

This was reported before via another user in https://github.com/anthropics/claude-code/issues/28260, but it was closed as a duplicate, but I don't think that is correct. There was no useful comment on the ticket or it's duplicate and it's still and issue in the Claude Code v2.1.78.

Am I using --plugin-dir incorrectly? I'm using it how it's documented on https://code.claude.com/docs/en/plugins-reference.

What Should Happen?

I expect the plugin to load and be usable so that I can test the plugin changes before pushing them to my marketplace.

Error Messages/Logs

The plugin is loaded but with the error:

 my-plugin @ inline
  Scope: user
  Version: 0.0.0/local
  My Plugin Description

  Author: Mycompany
  Status: Enabled

  Components:
    Error: Marketplace 'inline' not found in configuration. Available marketplaces: claude-plugins-official, mycompany-stable`

Steps to Reproduce

claude --plugin-dir=/path/to/my-plugin

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.78.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_