From 4826222d4d58a5c719f06af9d1b0a5e65f56a962 Mon Sep 17 00:00:00 2001
From: Sydney Runkle <sydneymarierunkle@gmail.com>
Date: Mon, 9 Mar 2026 11:00:34 -0400
Subject: [PATCH] raise on update input

---
 libs/langgraph/langgraph/pregel/_loop.py |  8 ++++++++
 libs/langgraph/tests/test_pregel.py      | 24 ++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/libs/langgraph/langgraph/pregel/_loop.py b/libs/langgraph/langgraph/pregel/_loop.py
index 79201d0d6..32e47c4bd 100644
--- a/libs/langgraph/langgraph/pregel/_loop.py
+++ b/libs/langgraph/langgraph/pregel/_loop.py
@@ -637,6 +637,14 @@ class PregelLoop:
 
         # map command to writes
         if isinstance(self.input, Command):
+            if self.input.resume is not None and self.input.update:
+                raise ValueError(
+                    "Command(resume=..., update=...) is not allowed as graph input. "
+                    "Use Command(resume=...) to resume execution, or use "
+                    "graph.update_state(...) to update state before resuming. "
+                    "Note: Command(update=...) can still be used as a return "
+                    "value from a node to update graph state."
+                )
             if (resume := self.input.resume) is not None:
                 if not self.checkpointer:
                     raise RuntimeError(
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index 61eaa5116..5e19aa910 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -5850,6 +5850,30 @@ def test_task_before_interrupt_resume(
     assert result == {"answers": ["answer1", "answer2"]}
 
 
+def test_command_resume_with_update_raises(
+    sync_checkpointer: BaseCheckpointSaver,
+) -> None:
+    """Test that Command(resume=..., update=...) raises InvalidUpdateError
+    when used as graph input."""
+
+    @entrypoint(checkpointer=sync_checkpointer)
+    def workflow(inputs: str) -> str:
+        answer = interrupt("question")
+        return answer
+
+    config = {"configurable": {"thread_id": "1"}}
+
+    # First invocation triggers interrupt
+    result = workflow.invoke("start", config=config)
+    assert "__interrupt__" in result
+
+    # Resuming with both resume and update should raise
+    with pytest.raises(ValueError, match="Command\\(resume=.*update="):
+        workflow.invoke(
+            Command(resume="answer", update={"foo": "bar"}), config=config
+        )
+
+
 def test_multiple_tasks_before_interrupt_resume(
     sync_checkpointer: BaseCheckpointSaver,
 ) -> None: