Removed marketplace namespace is incorrectly applied to personal and built-in skills

Summary

After removing the oh-my-mermaid plugin and marketplace, Codex still assigns the oh-my-mermaid: namespace to every skill under ~/.codex/skills, including built-in .system skills.

The affected SKILL.md files do not declare this namespace, and none of the directories are symlinks into the plugin. This appears to be a skill-source attribution issue at the skills-root level.

Environment

• Codex CLI: 0.145.0-alpha.18
• Surface: Codex desktop app / ChatGPT desktop app
• OS: macOS 27.0.0, arm64

Steps to reproduce

1. Configure/install the oh-my-mermaid marketplace/plugin.
2. Place ordinary personal skills under ~/.codex/skills/<skill-name>/SKILL.md.
3. Remove the plugin and marketplace:

``console
codex plugin marketplace remove oh-my-mermaid
``

1. Fully quit the desktop app and restart it.
2. Start a new task and inspect the injected available-skills list.

Actual behavior

Personal skills are still exposed as, for example:

oh-my-mermaid:journal-rank-lookup
oh-my-mermaid:academic-humanizer

Built-in skills are also incorrectly exposed with the same namespace, for example:

oh-my-mermaid:openai-docs
oh-my-mermaid:imagegen
oh-my-mermaid:skill-creator

The skill-root mapping points to the normal directories:

~/.codex/skills
~/.codex/skills/.system

The frontmatter contains only an unqualified name such as:

---
name: journal-rank-lookup
---

Expected behavior

Skills stored directly under ~/.codex/skills should not inherit the namespace of a removed marketplace. Built-in .system skills should retain their normal Codex/system attribution.

Diagnostics performed

• codex plugin list reports oh-my-mermaid@oh-my-mermaid as not installed before marketplace removal.
• codex plugin marketplace remove oh-my-mermaid succeeds and removes the marketplace snapshot.
• oh-my-mermaid no longer appears in ~/.codex/config.toml.
• ~/.codex/.tmp/marketplaces/oh-my-mermaid no longer exists.
• The desktop app was fully quit and restarted.
• codex doctor reports healthy configuration and state databases, and no persistent background app-server.
• The incorrect namespace remains in a newly injected skills catalog after restart.

Impact

The underlying skill files and scripts still execute from the correct personal paths, but the displayed/invoked names are misleading and appear to attribute unrelated personal and built-in skills to a third-party plugin.