[BUG] Unknown plugin "fizz@testmkt-marketplace" appeared in blocklist.json without user installation [MAC] [LINUX

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?

Summary

A plugin entry appeared in my ~/.claude/plugins/blocklist.json without me knowingly installing it. I have no recollection of adding this plugin and it does not correspond to any action I took.

Plugin details

• Plugin: fizz@testmkt-marketplace
• Date added (per JSON): 2026-02-12T00:00:00.000Z
• Reason in file: security
• Text in file: this is a security test

File content

{
  "plugin": "fizz@testmkt-marketplace",
  "added_at": "2026-02-12T00:00:00.000Z",
  "reason": "security",
  "text": "this is a security test"
}

Environment
OS: macOS Darwin 25.2.0
Interface: Antigravity (Claude Code client)
No matching plugin was found installed anywhere in ~/.claude/
No network calls or malicious code were found in a full audit of skills and scripts

Questions
Is testmkt-marketplace a known or official marketplace?
How can a plugin appear in the blocklist without user action?
Was this entry injected by a third party, or is it an internal Anthropic test artifact?

I ran a full security audit of my environment and found no active compromise, but the unexplained origin of this entry is concerning.

### What Should Happen?

Plugin entries should only appear in blocklist.json as a result of explicit user action (e.g., manually blocking a plugin). No plugin should be registered — even in a blocked state — without the user knowingly installing or interacting with it first. If the system adds entries automatically for internal testing or security purposes, the user should be notified.


### Error Messages/Logs

```shell

Steps to Reproduce

Unknown. The entry appeared without any deliberate action on my part. I did not install, search for, or interact with any plugin named "fizz" or from the "testmkt-marketplace" source.

The entry was discovered during a routine security audit of ~/.claude/plugins/blocklist.json on 2026-03-07.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Using Antigravity client (version unknown)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_