First try on WasmFS using petersalomonsen/wasm-git with emscripten 3.1.49

+server.js

// place this at src/routes/git-proxy/[...path]/+server.js
// modified from
// https://github.com/petersalomonsen/wasm-git/blob/master/examples/webserverwithgithubproxy.js

import https from 'node:https'
import { Readable } from 'node:stream'

import { error } from '@sveltejs/kit'

/**
 * Simple webserver with proxy to github.com
 */

/** @type {import('./$types').RequestHandler} */
export function fallback({ params, request }) {
  const { path: pathname } = params

  const query = new URL(request.url).searchParams
  const path = '/' + pathname + '?' + query

  if (path.indexOf('git-upload') != -1 ||
      path.indexOf('git-receive') != -1) {
    const options = {
      hostname: 'github.com',
      port: 443,
      path: path,
      method: request.method,
    };

    console.log(`Proxying ${options.method} request to ${options.hostname} with path ${options.path}`);

    return new Promise(resolve => {
      const proxy = https.request(options, incoming => {
        const readable = Readable.toWeb(incoming)
        resolve(new Response(readable))
      })

      if (options.method == 'GET') {
        proxy.end()
      } else {
        const requestBody =
          /** @type {import('node:stream/web').ReadableStream<Uint8Array>} */
          (request.body)
        Readable.fromWeb(requestBody).pipe(proxy, { end: true })
      }
    })
  } else {
    throw error(404, 'Not found')
  }
}

wasm-git.worker.js

export {}

function assertZero(/** @type {any} */n) {
  if (n !== 0) {
    throw new Error(`Return value is not zero: ${n}`)
  }
}

function calculateTotalSize(
  /** @type {Record<number, Uint8Array | undefined>} */ map) {
  let size = 0
  for (let buf of Object.values(map)) {
    if (buf) size += buf.length
  }
  return size
}

// trick into that we are running in web (actually we are)
// @ts-ignore
self.window = {}

const Module = {
  locateFile(s) {
    if (s === 'lg2.wasm') {
      s = 'lg2-wasmfs.wasm'
    }
    return '/' + s
  },

  print(s) {
    postMessage({type: 'print', value: s})
  },

  printErr(v) {
    console.error(v)
  },
}

const module = await import('./lg2-wasmfs.js')

function makeAsyncFS(backends, JSFILEFS) {
  function wrapBackendImplAt(ptr, opts) {
    console.log(backends[ptr])
    return backends[ptr]
  }

  return {
    createBackend(opts) {
      const ptr = JSFILEFS.createBackend()
      backends[ptr] = wrapBackendImplAt(ptr, opts)
      return ptr
    }
  }
}


Module.onRuntimeInitialized = async () => {
  const lg = Module

  const {
    FS,
    JSFILEFS,
    wasmFS$backends,
    wasmFS$JSMemoryFiles } = Module

  console.warn(Object.keys(Module))
  console.warn(Object.keys(FS))

  const ASYNCFS = makeAsyncFS(wasmFS$backends, JSFILEFS)

  // to work around WasmFS's bug where newly-mounted FS has empty dir name
  // causing all operations using CWD to behave weirdly, as of emscripten 3.1.49
  assertZero(FS.mount(ASYNCFS, { }, '/.xxx'))
  assertZero(FS.rename('.xxx', 'working'))
  assertZero(FS.chdir('/working'))

  assertZero(
    FS.writeFile('/home/web_user/.gitconfig',
      '[user]\n' +
      'name = Test User\n' +
      'email = test@example.com'))

  assertZero(FS.chdir('/working'))
  console.log('dir', FS.cwd())

  const ref = 'ewxrjk/sftpserver'
  const repoUrl = new URL(`/git-proxy/${ref}.git`, self.location.toString()).toString()
  lg.callMain(['clone', repoUrl, 'testrepo'])
  assertZero(FS.chdir('testrepo'))
  lg.callMain(['log'])

  postMessage({type: 'readdir', value: FS.readdir('.')})

  // console.warn(wasmFS$backends)
  console.warn('total size', calculateTotalSize(wasmFS$JSMemoryFiles))
}

await module.default(Module)