[BUG] Plugin marketplace paths hardcoded as absolute paths, breaking devcontainer usage

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?

Description

Plugin marketplace metadata stores absolute file paths in known_marketplaces.json, causing ENOENT errors when Claude Code runs inside devcontainers with different usernames or mount paths.

## Environment

• Claude Code version: Latest
• Platform: Linux (WSL2)
• Context: Running inside VS Code devcontainer

## Root Cause

The file ~/.claude/plugins/known_marketplaces.json stores plugin locations as absolute paths:

```json
{
"claude-code-workflows": {
"source": {
"source": "git",
"url": "https://github.com/wshobson/agents.git"
},
"installLocation": "/home/hostuser/.claude/plugins/marketplaces/claude-code-workflows",
"lastUpdated": "2025-10-25T22:40:23.757Z"
}
}

  When running in a devcontainer with a different username (e.g., vscode, node), the absolute path becomes invalid even when the .claude directory is properly mounted.

### What Should Happen?

Plugins work because .claude directory is mounted

### Error Messages/Logs

```shell
Error ENOENT: no such file or directory, stat '/home/alice/.claude/plugins/marketplaces/claude-code-workflows'

Steps to Reproduce

Reproduction Steps

1. Install plugin marketplace on host system (e.g., running as user alice at /home/alice/.claude)
2. Create devcontainer with different remote user:

```json
{
"remoteUser": "vscode",
"mounts": [
"source=${localEnv:HOME}/.claude,target=/home/vscode/.claude,type=bind"
]
}

  3. Start devcontainer and run Claude Code
  4. Try to use any plugin from the marketplace

### Claude Model

None

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

2.0.27

### Platform

Anthropic API

### Operating System

Ubuntu/Debian Linux

### Terminal/Shell

WSL (Windows Subsystem for Linux)

### Additional Information

_No response_