review: loopd prints every startup notice before it binds; tests wait for "serving on"

The serve tests waited for the socket file, then killed `loopd` and read its stderr, but the
socket is bound before its mode is set and before "serving on" and the broker notice are printed,
so a kill in between lost those lines (`pointers` failed once under load in M5c-1 task 15). The
broker notice now comes before the bind, so "serving on" is the last startup line, and the tests
wait for it (`tests/support/serving.rs`).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/loopd/src/main.rs

@@ -102,6 +102,18 @@ fn run_serve(path: &Path) -> ExitCode {
         return ExitCode::from(1);
     }
 
+    // Every startup notice comes before the socket is bound, so "serving on" is the last line
+    // before loopd serves: a supervisor or test that waits for it has seen all the others.
+    let port: Box<dyn ToolPort> = match &cfg.broker.socket {
+        Some(socket) => Box::new(BrokerPort::new(
+            socket.clone(),
+            Duration::from_millis(cfg.broker.timeout_ms),
+        )),
+        None => {
+            eprintln!("{}", not_configured_line());
+            Box::new(NoBroker)
+        }
+    };
     if let Some(parent) = socket.parent()
         && let Err(e) = std::fs::create_dir_all(parent)
     {
@@ -121,16 +133,6 @@ fn run_serve(path: &Path) -> ExitCode {
     }
     eprintln!("loopd: serving on {}", socket.display());
 
-    let port: Box<dyn ToolPort> = match &cfg.broker.socket {
-        Some(socket) => Box::new(BrokerPort::new(
-            socket.clone(),
-            Duration::from_millis(cfg.broker.timeout_ms),
-        )),
-        None => {
-            eprintln!("{}", not_configured_line());
-            Box::new(NoBroker)
-        }
-    };
     let memory = Box::new(MemoryPort::new(cfg.memory_socket(), MEMORY_WAIT));
     let ctx = Arc::new(Context::new(cfg, client, port, Registry::m5a(), memory));
     if let Err(e) = channel::serve(listener, ctx) {