[BUG] Filesystem MCP server (remote-devices) fails all tool calls: outputSchema declares unsupported draft-07 dialect

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?

Every tool call to the filesystem MCP server (accessed via the remote-devices bridge in Cowork mode) fails immediately with a schema validation error, regardless of which tool is called. Tested with list_allowed_directories, list_directory, read_text_file, and write_file — all fail identically.

What Should Happen?

The filesystem tools should execute normally and return directory listings / file contents, as they did before 2026-08-22. The tool's outputSchema should validate correctly against the client's JSON Schema validator instead of failing before the call even reaches the server logic.

Error Messages/Logs

Error: Tool '<toolname>' has an invalid outputSchema: JSON Schema declares an unsupported dialect ("$schema": "http://json-schema.org/draft-07/schema#"). The default validator supports JSON Schema 2020-12 only; pass a pre-configured Ajv instance to AjvJs

Steps to Reproduce

1. Open Claude (Cowork mode) on Windows 11 with a connected folder/network drive (P:\)
2. Call any filesystem MCP tool, e.g. list_allowed_directories or list_directory
3. Observe the tool call fails immediately with the outputSchema error above
4. Repeat with other filesystem tools (read_text_file, write_file, etc.) — same error every time

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

N/A — using Claude (Cowork mode) via the Claude Desktop app, not the Claude Code CLI.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Reported to Anthropic support first; support confirmed this looks like a server-side draft-07 vs. 2020-12 schema mismatch and suggested filing here since it wasn't resolvable via client config or restart.

Related but not identical issues:

• #80094 (macOS, different symptom — outputSchema/structuredContent dispatch failure)
• #80252 (Windows, similar filesystem connector setup, but empty logs / no schema error mentioned)

Blocks a recurring automated task reading/writing files on a connected network drive (P:\).