brokerd, memoryd, gatewayd: a lock file keeps each to one instance

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/brokerd/tests/serve.rs

@@ -216,24 +216,6 @@ fn a_stale_socket_is_replaced() {
     );
 }
 
-#[test]
-fn a_second_brokerd_on_the_same_home_refuses_to_start() {
-    let home = Home::new("serve-twice", 900_000);
-    let _running = home.serve();
-    let second = home.run(&[]);
-    assert_eq!(second.status.code(), Some(1));
-    let text = stderr(&second);
-    assert!(text.contains("brokerd is already running"), "{text}");
-    assert!(
-        text.trim_end()
-            .ends_with("see docs/runbook.md#brokerd-already-running"),
-        "{text}"
-    );
-    // The first still has its sockets.
-    let frames = exchange(&home.admin(), 1, Message::Approvals(Empty {}));
-    assert!(matches!(frames[0].msg, Message::ApprovalList(_)));
-}
-
 #[test]
 fn it_answers_each_socket_and_refuses_the_other_kinds() {
     let home = Home::new("serve-kinds", 900_000);