chore: add more fixtures

api/tests/dto_fixtures/multiple_start_nodes.json

@@ -0,0 +1,17 @@
+{
+  "nodes": [
+    {
+      "id": "s1",
+      "type": "startCall",
+      "position": {"x": 0, "y": 0},
+      "data": {"name": "Start A", "prompt": "Greet path A.", "is_start": true}
+    },
+    {
+      "id": "s2",
+      "type": "startCall",
+      "position": {"x": 0, "y": 200},
+      "data": {"name": "Start B", "prompt": "Greet path B.", "is_start": true}
+    }
+  ],
+  "edges": []
+}

api/tests/test_workflow_graph_constraints.py

@@ -72,7 +72,14 @@ _SCENARIOS = [
     (
         "no_start_node",
         ["no_start_node"],
-        ["Workflow must have exactly one start node"],
+        ["Workflow has no start node"],
+    ),
+    # Two startCall nodes — surfaced separately from no_start_node so
+    # the editor can show a count-specific message.
+    (
+        "multiple_start_nodes",
+        ["multiple_start_nodes:2"],
+        ["Workflow has 2 start nodes"],
     ),
 ]