filter virtual start node event for snippet draft run.

api/services/snippet_generate_service.py

@@ -80,6 +80,50 @@ class SnippetGenerateService:
     # Specific ID for the injected virtual Start node so it can be recognised
     _VIRTUAL_START_NODE_ID = "__snippet_virtual_start__"
 
+    @classmethod
+    def _is_virtual_start_event(cls, message: Mapping[str, Any] | str) -> bool:
+        """
+        Return True when *message* is a snippet-only virtual Start node event.
+
+        The virtual Start node is injected purely for snippet execution and is
+        not part of the persisted draft graph. Filter its node lifecycle events
+        out of the SSE stream so the frontend only receives nodes that exist on
+        the canvas.
+        """
+        if not isinstance(message, Mapping):
+            return False
+
+        if message.get("event") not in {"node_started", "node_finished"}:
+            return False
+
+        data = message.get("data")
+        if not isinstance(data, Mapping):
+            return False
+
+        return data.get("node_id") == cls._VIRTUAL_START_NODE_ID
+
+    @classmethod
+    def _filter_virtual_start_events(
+        cls,
+        response: Mapping[str, Any] | Generator[Mapping[str, Any] | str, None, None],
+    ) -> Mapping[str, Any] | Generator[Mapping[str, Any] | str, None, None]:
+        """
+        Drop snippet virtual Start node lifecycle events from stream responses.
+
+        Blocking responses are returned unchanged because they never expose the
+        injected node as a standalone event payload.
+        """
+        if isinstance(response, Mapping):
+            return response
+
+        def _stream() -> Generator[Mapping[str, Any] | str, None, None]:
+            for message in response:
+                if cls._is_virtual_start_event(message):
+                    continue
+                yield message
+
+        return _stream()
+
     @classmethod
     def generate(
         cls,
@@ -119,16 +163,18 @@ class SnippetGenerateService:
         # Adapt snippet to App-like interface for WorkflowAppGenerator
         app_proxy = _SnippetAsApp(snippet)
 
+        response = WorkflowAppGenerator().generate(
+            app_model=app_proxy,  # type: ignore[arg-type]
+            workflow=workflow,
+            user=user,
+            args=args,
+            invoke_from=invoke_from,
+            streaming=streaming,
+            call_depth=0,
+        )
+
         return WorkflowAppGenerator.convert_to_event_stream(
-            WorkflowAppGenerator().generate(
-                app_model=app_proxy,  # type: ignore[arg-type]
-                workflow=workflow,
-                user=user,
-                args=args,
-                invoke_from=invoke_from,
-                streaming=streaming,
-                call_depth=0,
-            )
+            cls._filter_virtual_start_events(response)
         )
 
     @classmethod

api/tests/unit_tests/services/test_snippet_generate_service.py

@@ -0,0 +1,67 @@
+from types import SimpleNamespace
+
+from core.app.entities.app_invoke_entities import InvokeFrom
+from services.snippet_generate_service import SnippetGenerateService
+
+
+def test_generate_filters_virtual_start_events(monkeypatch) -> None:
+    snippet = SimpleNamespace(id="snippet-id", tenant_id="tenant-id")
+    user = SimpleNamespace(id="user-id")
+    workflow = SimpleNamespace(id="workflow-id")
+
+    monkeypatch.setattr(
+        "services.snippet_generate_service.SnippetService",
+        lambda: SimpleNamespace(get_draft_workflow=lambda *, snippet: workflow),
+    )
+    monkeypatch.setattr(
+        SnippetGenerateService,
+        "_ensure_start_node",
+        classmethod(lambda cls, workflow, snippet: workflow),
+    )
+
+    stream_messages = iter(
+        [
+            {"event": "workflow_started", "data": {"id": "run-1"}},
+            {
+                "event": "node_started",
+                "data": {"node_id": SnippetGenerateService._VIRTUAL_START_NODE_ID, "title": "Start"},
+            },
+            {
+                "event": "node_finished",
+                "data": {"node_id": SnippetGenerateService._VIRTUAL_START_NODE_ID, "status": "succeeded"},
+            },
+            {"event": "node_started", "data": {"node_id": "code-node", "title": "Code"}},
+            {"event": "node_finished", "data": {"node_id": "code-node", "status": "succeeded"}},
+            {"event": "workflow_finished", "data": {"id": "run-1", "status": "succeeded"}},
+        ]
+    )
+
+    monkeypatch.setattr(
+        "services.snippet_generate_service.WorkflowAppGenerator.generate",
+        lambda self, **kwargs: stream_messages,
+    )
+    monkeypatch.setattr(
+        "services.snippet_generate_service.WorkflowAppGenerator.convert_to_event_stream",
+        lambda generator: list(generator),
+    )
+
+    response = SnippetGenerateService.generate(
+        snippet=snippet,
+        user=user,
+        args={"inputs": {}},
+        invoke_from=InvokeFrom.DEBUGGER,
+        streaming=True,
+    )
+
+    assert response == [
+        {"event": "workflow_started", "data": {"id": "run-1"}},
+        {"event": "node_started", "data": {"node_id": "code-node", "title": "Code"}},
+        {"event": "node_finished", "data": {"node_id": "code-node", "status": "succeeded"}},
+        {"event": "workflow_finished", "data": {"id": "run-1", "status": "succeeded"}},
+    ]
+
+
+def test_filter_virtual_start_events_returns_blocking_response_unchanged() -> None:
+    blocking_response = {"task_id": "task-1", "data": {"status": "succeeded"}}
+
+    assert SnippetGenerateService._filter_virtual_start_events(blocking_response) is blocking_response