[BUG] Cowork Windows: present_files returns "not accessible on the user's computer" for all files — blocks plugin installation

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?

mcp__cowork__present_files fails with "Cannot present file(s) — not accessible on the user's computer" for every file regardless of location, extension, or creation method. This completely blocks the plugin installation workflow since present_files is the only mechanism to deliver .plugin files with an install card.
The issue was not present yesterday (2026-04-16) on the same machine and plan. It appeared today (2026-04-17) with no user-side changes.
Environment

OS: Windows 11
Claude Desktop version: Current as of 2026-04-17
Plan: Max
Session type: Cowork with a mounted workspace folder

What Should Happen?

present_files should render a clickable file card in the chat. For .plugin files specifically, it should render an install card that lets the user browse plugin contents and accept installation.
Impact

Plugin installation is completely blocked. There is no alternative in-session mechanism to install a locally-built .plugin file. The plugin install directory (.remote-plugins/) is read-only from the agent's perspective.
All file delivery is blocked. Even non-plugin files (.docx, .xlsx, .txt) cannot be presented to the user.
This was the primary delivery mechanism recommended by the create-cowork-plugin skill.

Possibly related

#37713 (Cowork Dispatch sessions fully isolated — closed 2026-04-03, but symptoms persist)
#24859 (Cowork Windows plugin skills searched at wrong path)
#37169 (Upload plugin button hidden)

Error Messages/Logs

Steps to Reproduce

Open a Cowork session with a mounted folder
Have Claude create any file in the workspace folder (e.g., Write tool → test.txt)
Have Claude call mcp__cowork__present_files with that file's path
Result: "Cannot present 1 file(s) — not accessible on the user's computer"

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.111

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_