Custom URI scheme _claude_vscode_fs_right breaks C#/Roslyn analyzer (UriFormatException)

Description

The Claude Code VSCode extension's custom filesystem scheme _claude_vscode_fs_right:// causes System.UriFormatException in the C# language server (Roslyn/OmniSharp), breaking IntelliSense and diagnostics.

This is the same root cause as #1522, #21713, #7606, and #3381 — but affecting the C#/Roslyn language server, which has not been reported before.

Error

System.UriFormatException: Failed create URI from '_claude_vscode_fs_right:/path/to/workspace/...'

Repeated diagnostic request failures in the Roslyn analyzer whenever Claude Code diff views are active.

Root Cause

The _claude_vscode_fs_right:// URIs leak into workspace/didChangeWatchedFiles LSP notifications broadcast to all language servers. The _ prefix violates RFC 3986 / LSP spec, so any language server that validates URIs throws.

Environment

• VSCode 1.115.0
• Remote-SSH (Linux host)
• C# extension with Roslyn analyzer
• Claude Code VSCode extension (latest)

Impact

• C# IntelliSense breaks during/after diff views
• Roslyn analyzer emits repeated diagnostic failures
• In the observed case, errors started ~3 minutes before a Remote-SSH connection reset (not necessarily causal, but the error spam is disruptive)

Related Issues

• #1522 — rust-analyzer (closed by inactivity bot)
• #21713 — rust-analyzer (closed as dup)
• #7606 — Python LSP (closed as dup)
• #3381 — Windows variant (still open, 150+ comments)

All closed issues were auto-closed without a fix. The underlying bug persists across multiple language servers.