perf: unblock workers before the API router is built (#10711)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/src/main.rs

@@ -1629,6 +1629,10 @@ Windmill Community Edition {GIT_VERSION}
             }
         }
 
+        // `workers_f` must stay ahead of `server_f`: these are polled on one task in
+        // declaration order, and `run_server` yields once after handing over the base
+        // internal url so the workers get past that oneshot before it builds its router.
+        // Ordering `server_f` first makes them wait out the whole build instead.
         if mcp_mode {
             futures::try_join!(workers_f, server_f)?;
         } else {

backend/windmill-api/src/lib.rs

@@ -584,6 +584,16 @@ pub async fn run_server(
         (Router::new(), Router::new(), Option::<()>::None)
     };
 
+    // Workers block on this before pulling their first job, so it is released ahead of
+    // the router tree below. `try_join!` polls this future and `workers_f` on one task,
+    // so the yield is what lets them proceed; without it they wait out the whole
+    // synchronous build. A request arriving first queues in the bound listener's backlog.
+    if let Err(e) = port_tx.send(format!("http://localhost:{}", port)) {
+        tracing::error!("Failed to send port: {e:#}");
+        return Err(anyhow::anyhow!("Failed to send port, exiting early: {e:#}"));
+    }
+    tokio::task::yield_now().await;
+
     let mcp_list_tools_service = {
         #[cfg(feature = "mcp")]
         {
@@ -1181,11 +1191,6 @@ pub async fn run_server(
         name.map(|x| format!("name={x}")).unwrap_or_default()
     );
 
-    if let Err(e) = port_tx.send(format!("http://localhost:{}", port)) {
-        tracing::error!("Failed to send port: {e:#}");
-        return Err(anyhow::anyhow!("Failed to send port, exiting early: {e:#}"));
-    }
-
     // Announce this server is ready so coordinated restarts can detect a healthy peer.
     if server_mode {
         if let Err(e) = announce_server_started(&db).await {