Currently when you specify a listening port on "vercel dev", it will try that port and if it's in use will increment the port until it finds a free one. Sometimes that's undesired behavior, because you have multiple projects communicating with each other through configured endpoint Urls (often set in the environment). So,, for example, if I have a react app talking a vercel function service doing local development, I put the service URL (localhost plus a port number) in the environment config. But if for some reason the function service finds the port is in use, it increments the port number but the nextjs app doesn't know that, and it ends up talking to the wrong thing. It would be nice to have an option to say "abort startup if the specified listening port is not available".