fix: disable duplicate trigger nodes in workflow builder (#402)

* fix: disable duplicate trigger nodes in workflow builder

AddNodePanel: disable trigger buttons and show tooltip when a trigger
already exists on the canvas, using bySpecName to identify trigger-
category specs from the live node list.
useWorkflowState: preflight in saveWorkflow rejects saves with multiple
trigger nodes via a sonner toast before the network request is made.
text_chat_session_service: include the original exception message in
TextChatSessionExecutionError so the HTTP 500 detail surfaces the root
cause without DB inspection.

Closes #378

* style: format test_text_chat_session_service.py with ruff

* chore: retrigger CI checks

* fix(workflow): enforce node instance constraints

---------

Co-authored-by: Abhishek Kumar <abhishek@a6k.me>

api/tests/dto_fixtures/multiple_global_nodes.json

@@ -0,0 +1,23 @@
+{
+  "nodes": [
+    {
+      "id": "s1",
+      "type": "startCall",
+      "position": {"x": 0, "y": 0},
+      "data": {"name": "Start", "prompt": "Greet.", "is_start": true}
+    },
+    {
+      "id": "g1",
+      "type": "globalNode",
+      "position": {"x": 0, "y": 200},
+      "data": {"name": "Global A", "prompt": "Use a calm tone."}
+    },
+    {
+      "id": "g2",
+      "type": "globalNode",
+      "position": {"x": 0, "y": 400},
+      "data": {"name": "Global B", "prompt": "Keep answers short."}
+    }
+  ],
+  "edges": []
+}

api/tests/dto_fixtures/multiple_trigger_nodes.json

@@ -0,0 +1,23 @@
+{
+  "nodes": [
+    {
+      "id": "s1",
+      "type": "startCall",
+      "position": {"x": 0, "y": 0},
+      "data": {"name": "Start", "prompt": "Greet.", "is_start": true}
+    },
+    {
+      "id": "t1",
+      "type": "trigger",
+      "position": {"x": 0, "y": 200},
+      "data": {"name": "Trigger A", "trigger_path": "trigger_a"}
+    },
+    {
+      "id": "t2",
+      "type": "trigger",
+      "position": {"x": 0, "y": 400},
+      "data": {"name": "Trigger B", "trigger_path": "trigger_b"}
+    }
+  ],
+  "edges": []
+}

api/tests/test_mcp_create_workflow.py

@@ -0,0 +1,66 @@
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from api.mcp_server.tools.create_workflow import create_workflow
+
+
+@pytest.mark.asyncio
+async def test_create_workflow_rejects_duplicate_api_triggers():
+    user = MagicMock()
+    user.id = 1
+    user.selected_organization_id = 1
+    payload = {
+        "nodes": [
+            {
+                "id": "start-1",
+                "type": "startCall",
+                "position": {"x": 0, "y": 0},
+                "data": {"name": "Start", "prompt": "Greet."},
+            },
+            {
+                "id": "trigger-1",
+                "type": "trigger",
+                "position": {"x": 0, "y": 200},
+                "data": {"name": "Trigger A", "trigger_path": "support_west"},
+            },
+            {
+                "id": "trigger-2",
+                "type": "trigger",
+                "position": {"x": 0, "y": 400},
+                "data": {"name": "Trigger B", "trigger_path": "support_east"},
+            },
+        ],
+        "edges": [],
+    }
+
+    with (
+        patch(
+            "api.mcp_server.tools.create_workflow.authenticate_mcp_request",
+            AsyncMock(return_value=user),
+        ),
+        patch(
+            "api.mcp_server.tools.create_workflow.parse_code",
+            AsyncMock(
+                return_value={
+                    "ok": True,
+                    "workflowName": "duplicate-trigger-test",
+                    "workflow": payload,
+                }
+            ),
+        ),
+        patch(
+            "api.mcp_server.tools.create_workflow.reconcile_positions",
+            return_value=payload,
+        ),
+        patch(
+            "api.mcp_server.tools.create_workflow.db_client.create_workflow",
+            AsyncMock(),
+        ) as create_mock,
+    ):
+        result = await create_workflow(code="ignored")
+
+    assert result["created"] is False
+    assert result["error_code"] == "graph_validation"
+    assert "at most one API Trigger" in result["error"]
+    create_mock.assert_not_awaited()

api/tests/test_mcp_save_workflow.py

@@ -244,6 +244,58 @@ const only = wf.addTyped(endCall({ name: "only", prompt: "bye" }));
     update_mock.assert_not_awaited()
 
 
+@pytest.mark.asyncio
+async def test_graph_validation_catches_duplicate_api_triggers(mock_backends):
+    save_mock, update_mock = mock_backends
+    payload = {
+        "nodes": [
+            {
+                "id": "start-1",
+                "type": "startCall",
+                "position": {"x": 0, "y": 0},
+                "data": {"name": "Start", "prompt": "Greet."},
+            },
+            {
+                "id": "trigger-1",
+                "type": "trigger",
+                "position": {"x": 0, "y": 200},
+                "data": {"name": "Trigger A", "trigger_path": "support_west"},
+            },
+            {
+                "id": "trigger-2",
+                "type": "trigger",
+                "position": {"x": 0, "y": 400},
+                "data": {"name": "Trigger B", "trigger_path": "support_east"},
+            },
+        ],
+        "edges": [],
+    }
+
+    with (
+        patch(
+            "api.mcp_server.tools.save_workflow.parse_code",
+            AsyncMock(
+                return_value={
+                    "ok": True,
+                    "workflowName": _FakeWorkflowModel.name,
+                    "workflow": payload,
+                }
+            ),
+        ),
+        patch(
+            "api.mcp_server.tools.save_workflow.reconcile_positions",
+            return_value=payload,
+        ),
+    ):
+        result = await save_workflow(workflow_id=1, code="ignored")
+
+    assert result["saved"] is False
+    assert result["error_code"] == "graph_validation"
+    assert "at most one API Trigger" in result["error"]
+    save_mock.assert_not_awaited()
+    update_mock.assert_not_awaited()
+
+
 # ─── Workflow not found / unauthorized ───────────────────────────────────
 
 

api/tests/test_node_specs.py

@@ -414,4 +414,9 @@ def test_to_mcp_dict_retains_authoring_signal_startcall():
     ]
 
     # graph_constraints drops its null sub-fields.
-    assert projected["graph_constraints"] == {"min_incoming": 0, "max_incoming": 0}
+    assert projected["graph_constraints"] == {
+        "min_incoming": 0,
+        "max_incoming": 0,
+        "min_instances": 1,
+        "max_instances": 1,
+    }

api/tests/test_qa_analysis_non_dict_response.py

@@ -42,15 +42,15 @@ async def test_whole_call_qa_tolerates_array_llm_response():
             "resolve_llm_config",
             new=AsyncMock(return_value=("openai", "gpt-4o", "sk-test", {})),
         ),
-        patch.object(qa_analysis, "create_llm_service_from_provider", return_value=object()),
+        patch.object(
+            qa_analysis, "create_llm_service_from_provider", return_value=object()
+        ),
         patch.object(
             qa_analysis,
             "_run_llm_inference",
             new=AsyncMock(return_value='["tag1", "tag2"]'),
         ),
-        patch.object(
-            qa_analysis, "setup_langfuse_parent_context", return_value=None
-        ),
+        patch.object(qa_analysis, "setup_langfuse_parent_context", return_value=None),
         patch.object(qa_analysis, "add_qa_span_to_trace", return_value=None),
         patch.object(qa_analysis.logger, "warning", warning_mock),
     ):

api/tests/test_text_chat_session_service.py

@@ -9,6 +9,7 @@ from api.services.workflow.text_chat_session_service import (
     TextChatTurnNotFoundError,
     _reload_text_chat_session,
     build_pending_text_chat_turn,
+    execute_pending_text_chat_turn,
     truncate_text_chat_future_turns,
     validate_text_chat_turn_cursor,
 )
@@ -77,6 +78,36 @@ async def test_reload_text_chat_session_uses_run_id_to_resolve_organization(
     get_text_session.assert_awaited_once_with(123, organization_id=77)
 
 
+@pytest.mark.asyncio
+async def test_execute_pending_turn_surfaces_original_exception_message(monkeypatch):
+    session = WorkflowRunTextSessionModel(workflow_run_id=42)
+    session.session_data = {
+        "turns": [{"id": "turn-1", "status": "pending"}],
+        "cursor_turn_id": "turn-1",
+    }
+    session.checkpoint = None
+
+    monkeypatch.setattr(
+        text_chat_session_service,
+        "execute_text_chat_pending_turn",
+        AsyncMock(side_effect=RuntimeError("Workflow has 2 start nodes")),
+    )
+    monkeypatch.setattr(
+        text_chat_session_service,
+        "_mark_pending_turn_failed",
+        AsyncMock(),
+    )
+
+    with pytest.raises(
+        TextChatSessionExecutionError, match="Workflow has 2 start nodes"
+    ):
+        await execute_pending_text_chat_turn(
+            workflow_id=1,
+            run_id=42,
+            text_session=session,
+        )
+
+
 @pytest.mark.asyncio
 async def test_reload_text_chat_session_raises_when_run_organization_is_missing(
     monkeypatch,

api/tests/test_workflow_create_route.py

@@ -47,3 +47,38 @@ def test_create_workflow_rejects_invalid_trigger_path_before_db_write():
     assert detail["errors"][0]["field"] == "data.trigger_path"
     assert "single URL path segment" in detail["errors"][0]["message"]
     assert mock_db.mock_calls == []
+
+
+def test_create_workflow_rejects_duplicate_api_triggers_before_db_write():
+    app = _make_test_app()
+    client = TestClient(app)
+
+    with patch("api.routes.workflow.db_client") as mock_db:
+        response = client.post(
+            "/workflow/create/definition",
+            json={
+                "name": "Support Agent",
+                "workflow_definition": {
+                    "nodes": [
+                        {
+                            "id": "trigger-1",
+                            "type": "trigger",
+                            "data": {"trigger_path": "support_west"},
+                        },
+                        {
+                            "id": "trigger-2",
+                            "type": "trigger",
+                            "data": {"trigger_path": "support_east"},
+                        },
+                    ],
+                    "edges": [],
+                },
+            },
+        )
+
+    assert response.status_code == 422
+    detail = response.json()["detail"]
+    assert detail["is_valid"] is False
+    assert detail["errors"][0]["kind"] == "workflow"
+    assert "at most one API Trigger" in detail["errors"][0]["message"]
+    assert mock_db.mock_calls == []

api/tests/test_workflow_graph_constraints.py

@@ -72,14 +72,24 @@ _SCENARIOS = [
     (
         "no_start_node",
         ["no_start_node"],
-        ["Workflow has no start node"],
+        ["Workflow must have at least one Start Call"],
     ),
     # 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"],
+        ["Workflow can have at most one Start Call"],
+    ),
+    (
+        "multiple_trigger_nodes",
+        ["max_instances_1:trigger:2"],
+        ["Workflow can have at most one API Trigger"],
+    ),
+    (
+        "multiple_global_nodes",
+        ["max_instances_1:globalNode:2"],
+        ["Workflow can have at most one Global Node"],
     ),
 ]
 
@@ -122,3 +132,35 @@ def test_workflow_graph_rejects_violations(name, expected_graph_messages):
         assert any(expected in m for m in actual_messages), (
             f"Expected substring {expected!r} not found in graph errors: {actual_messages}"
         )
+
+
+def test_workflow_graph_can_skip_duplicate_api_trigger_check_for_runtime():
+    raw, _ = _load("multiple_trigger_nodes")
+    dto = ReactFlowDTO.model_validate_json(raw)
+
+    WorkflowGraph(dto, skip_instance_constraints_for={"trigger"})
+
+
+def test_workflow_graph_start_semantics_come_from_node_type_not_legacy_flag():
+    dto = ReactFlowDTO.model_validate(
+        {
+            "nodes": [
+                {
+                    "id": "start-1",
+                    "type": "startCall",
+                    "position": {"x": 0, "y": 0},
+                    "data": {
+                        "name": "Start",
+                        "prompt": "Greet.",
+                        "is_start": False,
+                    },
+                }
+            ],
+            "edges": [],
+        }
+    )
+
+    graph = WorkflowGraph(dto)
+
+    assert graph.start_node_id == "start-1"
+    assert graph.nodes["start-1"].is_start is True