[Bug] sandbox.connect() fails with "Unexpected server response: 101" on Bun runtime + express

[nalaso]

When using @codesandbox/sdk (v2.4.2) with Bun runtime (v1.3.4), calling sandbox.connect() throws:

error: Unexpected server response: 101
  at errorListener (node_modules/@codesandbox/sdk/dist/esm/index.js:8444:16)

[testListFiles] Error: 8439 |     cleanInitialListeners();
8440 |     resolve(new WebSocketClient(ws));
8441 |   };
8442 |   const errorListener = ({ message }) => {
8443 |     cleanInitialListeners();
8444 |     reject(new Error(message));
                      ^
error: Unexpected server response: 101

Steps to Reproduce:

Create a backend server using Bun + Express
Install @codesandbox/sdk
Resume a sandbox and attempt to connect:

const sdk = new CodeSandbox(apiKey);
const sandbox = await sdk.sandboxes.resume(sandboxId);
console.log(sandbox.bootupType); // Logs "RUNNING"
const client = await sandbox.connect(); // ❌ Fails here

Expected: WebSocket connection should succeed.

Actual: Throws "Unexpected server response: 101" even though sandbox is already RUNNING.

Environment:

SDK: @codesandbox/sdk@2.4.2
Runtime: Bun 1.3.4
OS: macOS