VS Code auto starting plug/bandit webserver

Hello All. I am looking at using Elixir to build a game server for a side project.
The plan is to use Websockets for the greatest mix of compatibility and security.

So found a simple hello world test and put it into vscode (running on Mac).
When I tried to launch it from the command line VS Code had already launched the webserver automatically.

Can someone explain to me what is happening? Not sure if it is a misconfiguration of mix or something else.

Code bellow. Thanks All!

# mix.exs
defmodule PlugServerProto.MixProject do
  use Mix.Project

  def project do
    [
      app: :plug_server_proto,
      version: "0.1.0",
      elixir: "~> 1.17",
      start_permanent: Mix.env() == :prod,
      deps: deps()
    ]
  end

  # Run "mix help compile.app" to learn about applications.
  def application do
    [
      extra_applications: [:logger]
    ]
  end


  # Run "mix help deps" to learn about dependencies.
  defp deps do
    [
      {:bandit, "~> 1.0"}
      # {:dep_from_hexpm, "~> 0.3.0"},
      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
    ]
  end
end

# plug_server_proto.ex
defmodule PlugServerProto do
  require Logger
  require Router

  webserver = {Bandit, plug: Router, scheme: :http, port: 4000}
  {:ok, _} = Supervisor.start_link([webserver], strategy: :one_for_one)
  Logger.info("Plug now running on localhost:4000")
  Process.sleep(:infinity)
end

# echo_server.ex
defmodule EchoServer do
  def init(options) do
    {:ok, options}
  end

  def handle_in({"ping", [opcode: :text]}, state) do
    {:reply, :ok, {:text, "pong"}, state}
  end

  def terminate(:timeout, state) do
    {:ok, state}
  end
end

# router.ex
defmodule Router do
  use Plug.Router

  plug Plug.Logger
  plug :match
  plug :dispatch

  get "/" do
    send_resp(conn, 200, """
    Use the JavaScript console to interact using websockets

    sock  = new WebSocket("ws://localhost:4000/websocket")
    sock.addEventListener("message", console.log)
    sock.addEventListener("open", () => sock.send("ping"))
    """)
  end

  get "/websocket" do
    conn
    |> WebSockAdapter.upgrade(EchoServer, [], timeout: 60_000)
    |> halt()
  end

  match _ do
    send_resp(conn, 404, "not found")
  end
end