Add optional loop schedule input

tools/prompt_smoke.py

@@ -7752,6 +7752,22 @@ def smoke_node_runtime_contracts() -> None:
         "Node class and display registries are out of sync",
     )
     _expect(len(node_names) >= 50, "Node registry unexpectedly small")
+    _expect(
+        loop_nodes._explicit_loop_schedule("1,3,5", 5) == [1, 3, 5],
+        "Loop schedule should parse comma-separated indexes",
+    )
+    _expect(
+        loop_nodes._explicit_loop_schedule("2-4", 5) == [2, 3, 4],
+        "Loop schedule should expand inclusive ranges",
+    )
+    _expect(
+        loop_nodes._next_loop_index(4, 10, schedule="4,2") == (2, True),
+        "Loop schedule should preserve explicit order",
+    )
+    _expect(
+        loop_nodes._next_loop_index(2, 10, schedule="4,2") == (11, False),
+        "Loop schedule should stop after the last scheduled index",
+    )
 
     for node_name in node_names:
         node_class = sxcp_nodes.NODE_CLASS_MAPPINGS[node_name]