[BUG] --plugin-dir does not take precedence over marketplace-installed plugin with same name

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

Bug Description

When running claude --plugin-dir=<path> with a plugin that has the same name as a marketplace-installed plugin, the marketplace version loads instead of the one at the specified path. The --plugin-dir flag should override (or at minimum merge with precedence over) marketplace-installed plugins.

Steps to Reproduce

1. Have a plugin installed via marketplace (e.g. ~/.claude/plugins/marketplaces/<org>/<plugin-name>/, version 2.0.0)
2. Have a local development copy of the same plugin at a different path (e.g. ~/dev/my-plugin/, version 1.0.0) that contains an agent definition not present in the marketplace version
3. Run: claude --plugin-dir=~/dev/my-plugin "invoke the agent only in the local version"
4. The marketplace version loads instead — the agent unique to the local version is unavailable

Expected Behavior

The plugin from --plugin-dir should take precedence over the marketplace-installed copy when they share the same plugin name. Agents and skills from --plugin-dir should be the ones loaded.

Actual Behavior

The marketplace version loads. Agent definitions only present in the --plugin-dir version are unavailable. The session resolves agent files from ~/.claude/plugins/marketplaces/... instead of the path passed via --plugin-dir.

Environment

• Claude Code version: 2.1.195
• OS: macOS (Darwin 25.5.0)
• Shell: zsh

Impact

• Plugin authors cannot test local changes without uninstalling the marketplace version first
• Users cannot pin an older plugin version via --plugin-dir if the marketplace has a newer one
• Makes iterative plugin development painful — the only workaround is rm -rf ~/.claude/plugins/marketplaces/<org>/<name>