chore: replace spinloop with return to main loop

runtime/src/local_runqueue_minheap.c

@@ -82,21 +82,9 @@ local_runqueue_minheap_get_next()
 	struct sandbox_request *sandbox_request = NULL;
 	int                     sandbox_rc      = priority_queue_top(&local_runqueue_minheap, (void **)&sandbox);
 
-	if (sandbox_rc == -ENOENT) {
+	if (sandbox_rc == -ENOENT && global_request_scheduler_peek() < ULONG_MAX) {
 		/* local runqueue empty, try to pull a sandbox request */
-
-		/*
-		 * This is effectively the idle loop. A worker thread spinlocks on
-		 * the earliest deadline, checking for the condition that indicates that
-		 * it is empty.
-		 */
-		while (sandbox_request == NULL) {
-			/* Spin without taking the lock if the request queue is empty */
-			while (global_request_scheduler_peek() == ULONG_MAX)
-				;
-
 		if (global_request_scheduler_remove(&sandbox_request) < 0) goto done;
-		}
 
 		/* Try to allocate a sandbox, returning the request on failure */
 		sandbox = sandbox_allocate(sandbox_request);