Cowork: plugin install from UI does not persist after restart

Bug Description

When installing a marketplace plugin from the Cowork (Claude Desktop) UI, the plugin appears installed during the current session but disappears after closing and reopening the app. The installation does not persist across restarts.

Steps to Reproduce

1. Open Claude Desktop (Cowork)
2. Go to Settings → Plugins
3. Find a plugin from a custom marketplace (e.g. escritos-judiciales@estudio-plugins)
4. Click Install — plugin appears correctly in the UI
5. Close Claude Desktop completely
6. Reopen Claude Desktop
7. The plugin is gone — not shown as installed

Root Cause

After investigating, the issue is that the UI install does not write to installed_plugins.json located at:

~/Library/Application Support/Claude/local-agent-mode-sessions/<session-id>/<sub-id>/cowork_plugins/installed_plugins.json

Other plugins that were installed in a previous session (and DO persist) have entries in this file with scope, installPath, version, installedAt, lastUpdated, and gitCommitSha. The newly installed plugin never gets written to this file, so on restart it's not recognized.

The .install-manifests/ directory and cache/ directory also don't get populated during a UI install — the install seems to happen only in memory.

Environment

• macOS 15.4 (Darwin 25.3.0)
• Claude Desktop (Cowork) — latest version as of 2026-03-30
• Custom marketplace: matiascliment-star/estudio-plugins (GitHub)
• Affected plugin: escritos-judiciales@estudio-plugins v1.1.0

Workaround

Manually adding the plugin entry to installed_plugins.json, creating the versioned cache directory, and writing the .install-manifests file makes the plugin persist. But this shouldn't be necessary — the UI install should handle all of this.