fix: frozen vertices crash with TypeError when no cache service available (#12409)

* fix: return CacheMiss() from fallback cache func so frozen vertices rebuild when no cache service

Fixes #12408

* fix: address review feedback on frozen vertex fix

- Use graph.arun() in test to exercise the process() path
- Make set_cache_func in process() return True for consistency with astep()

* [autofix.ci] apply automated fixes

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

src/lfx/src/lfx/graph/graph/base.py

@@ -1457,7 +1457,7 @@ class Graph:
         else:
             # Fallback no-op cache functions for tests or when service unavailable
             async def get_cache_func(*args, **kwargs):  # noqa: ARG001
-                return None
+                return CacheMiss()
 
             async def set_cache_func(*args, **kwargs) -> bool:  # noqa: ARG001
                 return True
@@ -1682,10 +1682,10 @@ class Graph:
         else:
             # Fallback no-op cache functions for tests or when service unavailable
             async def get_cache_func(*args, **kwargs):  # noqa: ARG001
-                return None
+                return CacheMiss()
 
-            async def set_cache_func(*args, **kwargs):
-                pass
+            async def set_cache_func(*args, **kwargs) -> bool:  # noqa: ARG001
+                return True
 
         await self.initialize_run()
         lock = asyncio.Lock()

src/lfx/tests/unit/graph/test_frozen_vertex.py

@@ -0,0 +1,46 @@
+import copy
+import json
+from pathlib import Path
+
+import pytest
+from lfx.graph import Graph
+
+
+@pytest.fixture
+def simple_chat_flow():
+    """Load the simple chat JSON test data."""
+    test_data_dir = Path(__file__).parent.parent.parent / "data"
+    json_path = test_data_dir / "simple_chat_no_llm.json"
+    with json_path.open() as f:
+        return json.load(f)
+
+
+@pytest.fixture
+def frozen_chat_flow(simple_chat_flow):
+    """Create a flow with a frozen vertex (ChatOutput)."""
+    flow = copy.deepcopy(simple_chat_flow)
+    for node in flow["data"]["nodes"]:
+        if node["data"]["node"].get("display_name") == "Chat Output":
+            node["data"]["node"]["frozen"] = True
+    return flow
+
+
+@pytest.mark.asyncio
+async def test_frozen_vertex_rebuilds_when_no_cache_service(frozen_chat_flow):
+    """A frozen vertex should rebuild gracefully when no cache service is available.
+
+    When running standalone (no server), chat_service is None. The fallback
+    get_cache_func should return CacheMiss so frozen vertices fall through
+    to the build path instead of crashing with TypeError.
+
+    Reproduces: https://github.com/langflow-ai/langflow/issues/12408
+    """
+    graph = Graph.from_payload(frozen_chat_flow)
+
+    # Verify the vertex is actually frozen
+    frozen_vertices = [v for v in graph.vertices if v.frozen]
+    assert len(frozen_vertices) > 0, "Expected at least one frozen vertex"
+
+    # Use arun which goes through process(), the same path as arun_flow_from_json
+    results = await graph.arun(inputs=[{"input_value": "hello"}])
+    assert len(results) > 0