[BUG] Marketplace plugins fail to load skills in Cowork -- zip upload of same plugin works fine

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Summary

All plugins installed from the marketplace fail to load their skills in Cowork sessions. The same plugin files, exported as a zip and uploaded via "Add plugin > Upload", work perfectly. This suggests the marketplace delivery pipeline is not properly mounting skill files into the Cowork container.

Environment

• Platform: macOS (Darwin 25.2.0)
• Claude Desktop: Latest version (Opus 4.6)
• Date: March 26, 2026

Steps to Reproduce

1. Install any plugin from the marketplace (e.g., sabai-remotion from sabai-claude-marketplace)
2. Open a new Cowork session
3. Invoke a plugin skill (e.g., /video)
4. Result: Either the loading spinner hangs indefinitely, or Claude responds with "It looks like there isn't a [plugin-name:skill] skill available in your current setup"

Expected Behavior

The skill should load and execute, just as it does when the same plugin is uploaded as a zip.

Actual Behavior

Two failure modes observed:

1. Skill not found: Claude says the skill isn't available, even though it appears in the Plugins menu (metadata is registered but SKILL.md files aren't mounted)
2. Spinner hangs: The loading spinner appears ("Working... Running skill...") and then stops without producing a response

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Proof: Same Plugin Works via Zip Upload

To confirm the plugin code is correct:

1. Exported the exact same plugin folder as a zip (cd plugins/sabai-remotion && zip -r sabai-remotion.zip .)
2. Uploaded via Plugins > Add plugin > Upload
3. Invoked /video -- works perfectly, skill loads and responds

This was tested with multiple plugins from the same marketplace. All fail when installed from the marketplace, all work when uploaded as zip.

Root Cause Analysis

The marketplace pipeline appears to register skill metadata in the system prompt (plugin shows in UI menu) but fails to mount the actual SKILL.md files in the container filesystem at runtime. The zip upload path bypasses this pipeline and correctly mounts all files.

This is consistent with the behavior described in:

• #26254 -- SKILL.md files not mounted in container despite metadata being registered
• #35641 -- /reload-plugins does not load skills from newly installed marketplace plugins
• #23910 -- Custom marketplace plugins show as enabled but fail to load skills

This may also be related to the active incident "Elevated connection reset errors in Cowork" (March 25, 2026).

Impact

• All marketplace plugins are affected, not just a specific one
• Plugin developers cannot reliably distribute plugins through the marketplace
• Users must manually export and re-upload plugins as a workaround
• Undermines trust in the marketplace as a distribution channel

Workaround

Export the plugin as a zip from within the plugin directory and upload via "Add plugin":

cd plugins/plugin-name
zip -r ~/Desktop/plugin-name.zip . -x "*/node_modules/*" -x "*/.DS_Store"

Then upload the zip in Claude Desktop via Plugins > Add plugin.

What Should Happen?

Download plugin should work.

Error Messages/Logs

Steps to Reproduce

1. Create market place
2. Download plugin
3. Call a skill with /

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Version 1.1.8629 (befdfc)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_