How to fix ERR_INVALID_URL_SCHEME when initializing C# in WebAssembly in node.js?

Here's a module to fix the problem (see explanation in comment at the top):

import Module from 'module';
import { fileURLToPath as originalFileURLToPath } from 'url';

// Vitest setup file that fixes ERR_INVALID_URL_SCHEME in Microsoft's 
// dotnet.native.js  module, to enable .NET WebAssembly in Node.js. 
// The issue: dotnet.js tries to call fileURLToPath() on import.meta.url,
// but in vitest, import.meta.url can be an http:// URL from the dev 
// server. (or so GPT5 tells me)
//
// e.g. fileURLToPath may be called with http://localhost:3000/src/_framework
//      and this code converts that to C:\Dev\[Project]\UI\src\_framework
const originalRequire = Module.prototype.require;

(Module.prototype as any).require = function(this: any, id: string) {
    const module = originalRequire.apply(this, arguments as any);
    
    if (id === 'url') {
        console.log('🔧 INTERCEPTED: url module require()');
        // Return a patched version of the url module
        return new Proxy(module, {
            get(target: any, prop: string) {
                if (prop === 'fileURLToPath') {
                    return function(urlArg: string | URL): string {
                        const urlString = typeof urlArg === 'string' ? urlArg : urlArg.href;
                        console.log('🔧 Patched fileURLToPath called with:', urlString);
                        
                        // If it's an HTTP URL from vitest dev server, convert it to a file path
                        if (urlString.startsWith('http://') || urlString.startsWith('https://')) {
                            // Vitest typically serves from the project root.
                            // Convert something like http://localhost:3000/src/_framework
                            // to [working directory]\src\_framework
                            const urlObj = new URL(urlString);
                            let path = urlObj.pathname; // e.g. "/src/_framework"
                            
                            // Assume we're in the parent directory of src
                            const projectRoot = process.cwd();
                            path = projectRoot + path;
                            
                            console.log('  → Converted to:', path);
                            return path;
                        }
                        
                        return originalFileURLToPath(urlArg);
                    };
                }
                return target[prop];
            }
        });
    }
    
    return module;
};

Then configure vitest to reference it:

export default defineConfig({
    ...
    // Vitest configuration: https://vitest.dev/config/
    test: {
        ...
        // Setup file to patch Node.js URL handling for .NET WebAssembly runtime
        setupFiles: ['./test/fix-csharp-in-tests.ts'],
    },
});

That should fix it. Remove console.log when you get it to work. Fun facts:

• don't call it fix-c#.ts as the # blocks it from loading.
• After I got my first C# test working, I still saw a red output "+ CategoryInfo : NotSpecified: (11:21:14 AM...work/dotnet.js.:String) [], RemoteException". No idea what it means.