Uninstalled plugin persists in Cowork cloud manifest (cowork-plugin-management ghost)

Bug Description

After uninstalling the cowork-plugin-management plugin via the Cowork UI (~2026-03-31), the plugin continues to appear in the available skills list on every turn. The plugin's skills (cowork-plugin-customizer, create-cowork-plugin) are listed in <available_skills> and in <system-reminder> skill listings despite being uninstalled.

Steps to Reproduce

1. Install the cowork-plugin-management plugin in Cowork
2. Uninstall it via the Cowork UI (Settings → Plugins → Uninstall)
3. Start a new Cowork session
4. Observe that the plugin's skills still appear in <available_skills> and <system-reminder> blocks

Expected Behavior

Uninstalled plugins should be fully removed from the Cowork cloud manifest and no longer appear in skill listings.

Actual Behavior

The plugin's two skills (cowork-plugin-customizer and create-cowork-plugin) continue to appear in every turn's system context. The skills are listed with paths under /mnt/.remote-plugins/ pointing to two different plugin IDs:

• plugin_016jbzs7aGBZSgBfSWhp4ToX
• plugin_016WWPoJ2p3XqHHHDvcXhp4p

Both entries reference the same skill names and descriptions, suggesting the plugin was registered twice and neither registration was cleaned up on uninstall.

Impact

• ~150 tokens/turn wasted on ghost plugin skills (cumulative cost across sessions)
• No user-side workaround available — the manifest is cloud-managed

Environment

• Claude Desktop (macOS)
• Cowork mode
• Uninstall date: ~2026-03-31

Related

Possibly related to #28554 (plugin lifecycle management)