Personal plugin upload: skills not registered in runtime

Description

When uploading a personal plugin via Customize → Upload plugin (ZIP file), the plugin appears in the UI (under "Personal plugins") but its skills are not registered in the runtime. The /skill-name slash command returns Unknown skill.

Steps to reproduce

1. Create a plugin with the standard structure:

``
.claude-plugin/plugin.json
skills/my-skill/SKILL.md
``

1. plugin.json:

``json
{
"name": "my-plugin",
"version": "1.0.0",
"description": "My plugin",
"author": { "name": "Author" },
"skills": ["skills/my-skill"]
}
``

1. skills/my-skill/SKILL.md:

``markdown
---
name: my-skill
description: "My skill description"
tools: [mcp__my-server__tool1, mcp__my-server__tool2]
---
Skill instructions here.
``

1. ZIP the plugin directory and upload via Customize → Browse plugins → Upload plugin
2. Plugin appears in the Customize UI under "Personal plugins" with correct name, skills list, and "Slash command + auto" trigger
3. Type /my-skill in conversation

Expected behavior

The skill should execute (same as marketplace plugins like frontend-design).

Actual behavior

Returns Unknown skill: my-skill.

Investigation

• ~/.claude/plugins/installed_plugins.json does not contain the uploaded personal plugin (only marketplace plugins like frontend-design appear)
• ~/.claude/plugins/cache/ has no directory for the personal plugin
• The skill is not in the runtime's available skills list despite showing in the UI
• Manually creating ~/.claude/skills/my-skill/SKILL.md with the same content does work — the skill immediately appears in the runtime

Workaround

Users can manually place the SKILL.md file in ~/.claude/skills/<skill-name>/SKILL.md. This is recognized by the runtime correctly.

Environment

• Claude Code desktop app (macOS)
• macOS 15 (Darwin 25.3.0)
• Plugin uploaded April 12, 2026
• Compared with frontend-design@claude-plugins-official which loads correctly from marketplace