[BUG] Claude Desktop crashes (Fatal error boundary) when opening sessions containing C# code diffs

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?

Claude Desktop crashes instantly when opening existing sessions that contain C# code diffs. The renderer fails to load the c_sharp syntax highlighter, which triggers a React fatal error boundary, killing the renderer. If the system tray option is disabled, the entire app quits and restarts in a crash loop.

What Should Happen?

The session should open normally. If the C# syntax highlighter fails to load, the app should gracefully fall back to plain text rendering without crashing the entire renderer.

Error Messages/Logs

From claude.ai-web.log:

[USER_CONTENT_RENDERER] Failed to load language: c_sharp - falling back to plain text (repeated ~30 times)
[USER_CONTENT_RENDERER] [SyntaxHighlightedDiff] Token without row: [object Object] (repeated ~30 times)
Error: Minified React error #185 (hydration mismatch)
[BOOTSTRAP] Fatal error boundary triggered [object Object]
Uncaught Error: Minified React error #418
MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 AutoUpdater.updaterState listeners added

From main.log:

Quitting app on main window close since tray is disabled
[CCD] Stopping 2 active session(s) on quit

Additional errors on every startup:

[CustomPlugins] Failed to fetch remote plugins: Failed to fetch browsable plugins (HTTP 404)
[REACT_QUERY_CLIENT] QueryClient error: path.conversation_uuid: Input should be a valid UUID, invalid character: found 'l' at 1
Failed to load session from local_8ff3b441-3059-4052-8408-b6b303ead1d4.json: Unexpected end of JSON input

Steps to Reproduce

1. Open Claude Desktop
2. Have an existing Claude Code session containing multiple C# code diffs (SyntaxHighlightedDiff blocks)
3. Click on that session to open it
4. App crashes immediately, renderer dies with React error #185
5. If system tray is disabled, the app fully quits and restarts — potentially looping

Claude Model

Claude Desktop: 1.1.3541 (MSIX)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Desktop: 1.1.3541 (MSIX)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Claude Code version

1. Claude Desktop: 1.1.3541 (MSIX)
2. CCD binary: 2.1.45
3. Node: 24.13.0
4. Platform: Windows 11 Pro (10.0.26100), x64
5. CPU: Intel Core i9-14900HX
6. RAM: 32 GB

Additional information

• The crash only happens on sessions with many C# diffs. New sessions and sessions without C# code work fine.
• Enabling the system tray option prevents the app from fully quitting on renderer crash, but the affected session still cannot be opened.
• An EventEmitter memory leak (MaxListenersExceededWarning) suggests listener cleanup is missing between re-render attempts after the error boundary triggers.
• The conversation_uuid validation error indicates local session IDs (prefixed with local_) are being passed to an API endpoint expecting standard UUIDs.
• The CustomPlugins HTTP 404 error occurs on every startup regardless of the crash issue.
• Clearing %APPDATA%\Claude\Cache and GPUCache did not resolve the issue.