fix(debug): self-referencing checkpoints when resuming streaming mid-thread

libs/langgraph/langgraph/pregel/loop.py

@@ -1,4 +1,4 @@
 import asyncio
 import concurrent.futures
 from collections import deque
 from contextlib import AsyncExitStack, ExitStack
@@ -250,13 +250,7 @@
             if self.config[CONF].get(CONFIG_KEY_CHECKPOINT_NS)
             else ()
         )
-        self.prev_checkpoint_config = (
-            self.checkpoint_config
-            if self.checkpoint_config
-            and CONF in self.checkpoint_config
-            and CONFIG_KEY_CHECKPOINT_ID in self.checkpoint_config[CONF]
-            else None
-        )
+        self.prev_checkpoint_config = None
 
     def put_writes(self, task_id: str, writes: Sequence[tuple[str, Any]]) -> None:
         """Put writes for a task, to be read by the next tick."""
@@ -740,6 +734,7 @@
                 **saved.config.get(CONF, {}),
             },
         }
+        self.prev_checkpoint_config = saved.parent_config
         self.checkpoint = saved.checkpoint
         self.checkpoint_metadata = saved.metadata
         self.checkpoint_pending_writes = (
@@ -867,6 +862,7 @@
                 **saved.config.get(CONF, {}),
             },
         }
+        self.prev_checkpoint_config = saved.parent_config
         self.checkpoint = saved.checkpoint
         self.checkpoint_metadata = saved.metadata
         self.checkpoint_pending_writes = (

libs/langgraph/tests/test_pregel.py

@@ -11584,6 +11584,66 @@ def baz(state: State):
     assert graph.invoke({"foo": "hello"}) == {"foo": "hello", "bar": "hello!"}
 
 
+def test_debug_retry():
+    class State(TypedDict):
+        messages: Annotated[list[str], operator.add]
+
+    def node(name):
+        def _node(state: State):
+            return {"messages": [f"entered {name} node"]}
+
+        return _node
+
+    builder = StateGraph(State)
+    builder.add_node("one", node("one"))
+    builder.add_node("two", node("two"))
+    builder.add_edge(START, "one")
+    builder.add_edge("one", "two")
+    builder.add_edge("two", END)
+
+    saver = MemorySaver()
+
+    graph = builder.compile(checkpointer=saver)
+
+    config = {"configurable": {"thread_id": "1"}}
+    graph.invoke({"messages": []}, config=config)
+
+    # re-run step: 1
+    target_config = next(
+        c.parent_config for c in saver.list(config) if c.metadata["step"] == 1
+    )
+    update_config = graph.update_state(target_config, values=None)
+
+    events = [*graph.stream(None, config=update_config, stream_mode="debug")]
+
+    checkpoint_events = list(
+        reversed([e["payload"] for e in events if e["type"] == "checkpoint"])
+    )
+
+    checkpoint_history = {
+        c.config["configurable"]["checkpoint_id"]: c
+        for c in graph.get_state_history(config)
+    }
+
+    def lax_normalize_config(config: Optional[dict]) -> Optional[dict]:
+        if config is None:
+            return None
+        return config["configurable"]
+
+    for stream in checkpoint_events:
+        stream_conf = lax_normalize_config(stream["config"])
+        stream_parent_conf = lax_normalize_config(stream["parent_config"])
+        assert stream_conf != stream_parent_conf
+
+        # ensure the streamed checkpoint == checkpoint from checkpointer.list()
+        history = checkpoint_history[stream["config"]["configurable"]["checkpoint_id"]]
+        history_conf = lax_normalize_config(history.config)
+        assert stream_conf == history_conf
+
+        history_parent_conf = lax_normalize_config(history.parent_config)
+        assert stream_parent_conf == history_parent_conf
+
+
 def test_debug_subgraphs():
     class State(TypedDict):
         messages: Annotated[list[str], operator.add]
@@ -11627,16 +11687,18 @@ def _node(state: State):
 
     assert len(checkpoint_events) == len(checkpoint_history)
 
-    def normalize_config(config: Optional[dict]) -> Optional[dict]:
+    def lax_normalize_config(config: Optional[dict]) -> Optional[dict]:
         if config is None:
             return None
         return config["configurable"]
 
     for stream, history in zip(checkpoint_events, checkpoint_history):
         assert stream["values"] == history.values
         assert stream["next"] == list(history.next)
-        assert normalize_config(stream["config"]) == normalize_config(history.config)
-        assert normalize_config(stream["parent_config"]) == normalize_config(
+        assert lax_normalize_config(stream["config"]) == lax_normalize_config(
+            history.config
+        )
+        assert lax_normalize_config(stream["parent_config"]) == lax_normalize_config(
             history.parent_config
         )
 

libs/langgraph/tests/test_pregel_async.py

@@ -9820,6 +9820,71 @@ async def node(input: State, config: RunnableConfig, store: BaseStore):
         )  # still overwriting the same one
 
 
+async def test_debug_retry():
+    class State(TypedDict):
+        messages: Annotated[list[str], operator.add]
+
+    def node(name):
+        async def _node(state: State):
+            return {"messages": [f"entered {name} node"]}
+
+        return _node
+
+    builder = StateGraph(State)
+    builder.add_node("one", node("one"))
+    builder.add_node("two", node("two"))
+    builder.add_edge(START, "one")
+    builder.add_edge("one", "two")
+    builder.add_edge("two", END)
+
+    saver = MemorySaver()
+
+    graph = builder.compile(checkpointer=saver)
+
+    config = {"configurable": {"thread_id": "1"}}
+    await graph.ainvoke({"messages": []}, config=config)
+
+    # re-run step: 1
+    async for c in saver.alist(config):
+        if c.metadata["step"] == 1:
+            target_config = c.parent_config
+            break
+    assert target_config is not None
+
+    update_config = await graph.aupdate_state(target_config, values=None)
+
+    events = [
+        c async for c in graph.astream(None, config=update_config, stream_mode="debug")
+    ]
+
+    checkpoint_events = list(
+        reversed([e["payload"] for e in events if e["type"] == "checkpoint"])
+    )
+
+    checkpoint_history = {
+        c.config["configurable"]["checkpoint_id"]: c
+        async for c in graph.aget_state_history(config)
+    }
+
+    def lax_normalize_config(config: Optional[dict]) -> Optional[dict]:
+        if config is None:
+            return None
+        return config["configurable"]
+
+    for stream in checkpoint_events:
+        stream_conf = lax_normalize_config(stream["config"])
+        stream_parent_conf = lax_normalize_config(stream["parent_config"])
+        assert stream_conf != stream_parent_conf
+
+        # ensure the streamed checkpoint == checkpoint from checkpointer.list()
+        history = checkpoint_history[stream["config"]["configurable"]["checkpoint_id"]]
+        history_conf = lax_normalize_config(history.config)
+        assert stream_conf == history_conf
+
+        history_parent_conf = lax_normalize_config(history.parent_config)
+        assert stream_parent_conf == history_parent_conf
+
+
 async def test_debug_subgraphs():
     class State(TypedDict):
         messages: Annotated[list[str], operator.add]