fix: ensure delivery of stop signal in scheduler by using await for command transmission

Author: nassor

src/scheduler.rs

@@ -389,9 +389,10 @@ where
     ///
     /// - [`CanoError::Workflow`] — the scheduler is not running
     pub async fn stop(&self) -> CanoResult<()> {
-        // Send stop signal — non-blocking; fails immediately if channel is full or disconnected
+        // Send stop signal — use send().await to ensure delivery for critical control-plane command.
+        // This is safe because stop signals are rare and waiting for queue space is acceptable.
         if let Some(tx) = self.command_tx.read().await.as_ref() {
-            tx.try_send(SchedulerCommand::Stop)
+            tx.send(SchedulerCommand::Stop).await
                 .map_err(|e| CanoError::Workflow(format!("Failed to send stop: {}", e)))?;
         } else {
             return Err(CanoError::Workflow(