release(checkpoint): 4.3.1 (#9447)

Version bump only. No library code changes in this PR.

Unreleased since `checkpoint==4.3.0`:

- #9383 - reject NUL bytes in store namespace labels

libs/checkpoint-conformance/uv.lock

@@ -279,7 +279,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },

libs/checkpoint-postgres/uv.lock

@@ -278,7 +278,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },

libs/checkpoint-sqlite/uv.lock

@@ -285,7 +285,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },

libs/checkpoint/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 description = "Library with base interfaces for LangGraph checkpoint savers."
 authors = []
 requires-python = ">=3.10"

libs/checkpoint/uv.lock

@@ -301,7 +301,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "." }
 dependencies = [
     { name = "langchain-core" },

libs/langgraph/langgraph/channels/delta.py

@@ -60,7 +60,7 @@ class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
         typ: The value type (e.g. `list`, `dict`). Inferred automatically
             from the outer type when used inside `Annotated[T, DeltaChannel(...)]`.
         snapshot_frequency: Every Nth update to this channel writes a snapshot
-            blob (default `1000`). Must be a positive int.
+            blob (default `100`). Must be a positive int.
     """
 
     __slots__ = ("value", "reducer", "snapshot_frequency")
@@ -71,7 +71,7 @@ class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
         reducer: Callable[[Any, Sequence[Any]], Any],
         typ: type[Value] | None = None,
         *,
-        snapshot_frequency: int = 1000,
+        snapshot_frequency: int = 100,
     ) -> None:
         if snapshot_frequency <= 0:
             raise ValueError(

libs/langgraph/langgraph/pregel/_executor.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import asyncio
 import concurrent.futures
 import time
+import weakref
 from collections.abc import Awaitable, Callable, Coroutine
 from contextlib import AbstractAsyncContextManager, AbstractContextManager, ExitStack
 from contextvars import copy_context
@@ -37,6 +38,13 @@ class Submit(Protocol[P, T]):
     ) -> concurrent.futures.Future[T]: ...
 
 
+# Futures whose exception a node's error handler took over; the executors
+# don't re-raise them on exit.
+SKIP_RERAISE_SET: weakref.WeakSet[concurrent.futures.Future | asyncio.Future] = (
+    weakref.WeakSet()
+)
+
+
 class BackgroundExecutor(AbstractContextManager):
     """A context manager that runs sync tasks in the background.
     Uses a thread pool executor to delegate tasks to separate threads.
@@ -111,7 +119,7 @@ class BackgroundExecutor(AbstractContextManager):
         if exc_type is None:
             # re-raise the first exception that occurred in a task
             for task, (_, reraise) in tasks.items():
-                if not reraise:
+                if not reraise or task in SKIP_RERAISE_SET:
                     continue
                 try:
                     task.result()
@@ -202,7 +210,7 @@ class AsyncBackgroundExecutor(AbstractAsyncContextManager):
         if exc_type is None:
             # re-raise the first exception that occurred in a task
             for task, (_, reraise) in tasks.items():
-                if not reraise:
+                if not reraise or task in SKIP_RERAISE_SET:
                     continue
                 try:
                     if exc := task.exception():

libs/langgraph/langgraph/pregel/_runner.py

@@ -43,7 +43,7 @@ from langgraph._internal._typing import MISSING
 from langgraph.constants import TAG_HIDDEN
 from langgraph.errors import GraphBubbleUp, GraphInterrupt, is_invalid_resume
 from langgraph.pregel._algo import Call
-from langgraph.pregel._executor import Submit
+from langgraph.pregel._executor import SKIP_RERAISE_SET, Submit
 from langgraph.pregel._retry import arun_with_retry, run_with_retry
 from langgraph.pregel._task_status import CONTROL_WRITES
 from langgraph.types import (
@@ -68,10 +68,6 @@ EXCLUDED_FRAME_FNAMES = (
     "concurrent/futures/_base.py",
 )
 
-SKIP_RERAISE_SET: weakref.WeakSet[concurrent.futures.Future | asyncio.Future] = (
-    weakref.WeakSet()
-)
-
 
 class FuturesDict(Generic[F, E], dict[F, PregelExecutableTask | None]):
     event: E
@@ -239,6 +235,8 @@ class PregelRunner:
                         fut.set_exception(exc)
                         futures.done.add(fut)
                 elif reraise and id(exc) not in self._handled_exception_ids:
+                    # let the caller stream this task's result before it raises
+                    yield
                     if tb := exc.__traceback__:
                         while tb.tb_next is not None and any(
                             tb.tb_frame.f_code.co_filename.endswith(name)
@@ -430,6 +428,8 @@ class PregelRunner:
                         fut.set_exception(exc)
                         futures.done.add(fut)
                 elif reraise and id(exc) not in self._handled_exception_ids:
+                    # let the caller stream this task's result before it raises
+                    yield
                     if tb := exc.__traceback__:
                         while tb.tb_next is not None and any(
                             tb.tb_frame.f_code.co_filename.endswith(name)

libs/langgraph/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.18"
 description = "Building stateful, multi-actor applications with LLMs"
 authors = []
 requires-python = ">=3.10"

libs/langgraph/tests/test_channels.py

@@ -20,6 +20,7 @@ from langgraph.errors import EmptyChannelError, InvalidUpdateError
 from langgraph.graph import START, StateGraph
 from langgraph.graph.message import _messages_delta_reducer
 from langgraph.graph.state import _get_channel
+from langgraph.pregel._checkpoint import delta_channels_to_snapshot
 from langgraph.types import Overwrite
 
 pytestmark = pytest.mark.anyio
@@ -342,6 +343,26 @@ def test_delta_channel_checkpoint_returns_missing() -> None:
 # ---------------------------------------------------------------------------
 
 
+@pytest.mark.parametrize("frequency", [None, 50, 1000])
+def test_delta_channel_snapshot_frequency(frequency: int | None) -> None:
+    spec = (
+        DeltaChannel(_messages_delta_reducer)
+        if frequency is None
+        else DeltaChannel(_messages_delta_reducer, snapshot_frequency=frequency)
+    )
+    expected = 100 if frequency is None else frequency
+    assert spec.snapshot_frequency == expected
+    channel = spec.from_checkpoint(MISSING)
+    channel.update([HumanMessage(content="hi", id="h1")])
+    assert channel.copy().snapshot_frequency == expected
+    for updates in (expected - 1, expected):
+        assert delta_channels_to_snapshot(
+            {"messages": channel},
+            {"messages": (updates, updates)},
+            {"messages": 1},
+        ) == ({"messages"} if updates == expected else set())
+
+
 def test_delta_channel_snapshot_version_based() -> None:
     """Snapshots fire when a channel accumulates `snapshot_frequency` updates.
 

libs/langgraph/tests/test_pregel.py

@@ -4346,6 +4346,25 @@ def test_enum_node_names():
     assert graph.invoke({"foo": "hello"}) == {"foo": "hello", "bar": "hello!"}
 
 
+@pytest.mark.parametrize("stream_mode", ["tasks", "debug"])
+def test_failing_task_result_is_streamed_before_the_error(stream_mode: str) -> None:
+    class State(TypedDict):
+        x: str
+
+    def failing(state: State) -> State:
+        raise ValueError("boom")
+
+    graph = StateGraph(State).add_node("failing", failing).add_edge(START, "failing")
+    errors = []
+    with pytest.raises(ValueError, match="boom"):
+        for chunk in graph.compile().stream({"x": ""}, stream_mode=stream_mode):
+            payload = chunk["payload"] if stream_mode == "debug" else chunk
+            if "error" in payload:
+                errors.append(payload["error"])
+
+    assert [type(error) for error in errors] == [ValueError]
+
+
 def test_debug_retry(sync_checkpointer: BaseCheckpointSaver):
     class State(TypedDict):
         messages: Annotated[list[str], operator.add]

libs/langgraph/tests/test_pregel_async.py

@@ -5809,6 +5809,60 @@ async def test_store_injected_async(
     )  # still overwriting the same one
 
 
+@pytest.mark.parametrize("stream_mode", ["tasks", "debug"])
+async def test_failing_task_result_is_streamed_before_the_error(
+    stream_mode: str,
+) -> None:
+    class State(TypedDict):
+        x: str
+
+    async def failing(state: State) -> State:
+        raise ValueError("boom")
+
+    graph = StateGraph(State).add_node("failing", failing).add_edge(START, "failing")
+    errors = []
+    with pytest.raises(ValueError, match="boom"):
+        async for chunk in graph.compile().astream({"x": ""}, stream_mode=stream_mode):
+            payload = chunk["payload"] if stream_mode == "debug" else chunk
+            if "error" in payload:
+                errors.append(payload["error"])
+
+    assert [type(error) for error in errors] == [ValueError]
+
+
+@pytest.mark.parametrize(
+    ("parallel", "stream_mode"), [(False, "custom"), (True, "values")]
+)
+async def test_graph_error_handler_recovers_on_the_executor_path(
+    parallel: bool, stream_mode: str
+) -> None:
+    class State(TypedDict):
+        x: str
+
+    async def failing(state: State) -> State:
+        raise ValueError("boom")
+
+    async def handler(state: State) -> Command:
+        return Command(update={"x": "handled"}, goto=END)
+
+    builder = (
+        StateGraph(State)
+        .add_node("failing", failing, error_handler=handler)
+        .add_edge(START, "failing")
+    )
+    if parallel:
+        builder.add_node("sibling", lambda state: {}).add_edge(START, "sibling")
+
+    chunks = [
+        chunk
+        async for chunk in builder.compile().astream(
+            {"x": ""}, stream_mode=[stream_mode, "values"]
+        )
+    ]
+
+    assert [c[-1] for c in chunks if c[0] == "values"][-1] == {"x": "handled"}
+
+
 async def test_debug_retry(async_checkpointer: BaseCheckpointSaver):
     class State(TypedDict):
         messages: Annotated[list[str], operator.add]

libs/langgraph/tests/test_retry.py

@@ -2097,6 +2097,47 @@ def test_graph_error_handler_can_route_with_command():
     assert result["foo"] == "handled_next"
 
 
+# Each case runs the failing node on the executor path instead of the
+# single-task fast path.
+@pytest.mark.parametrize(
+    ("parallel", "stream_mode", "subgraphs"),
+    [
+        (False, "custom", False),
+        (False, "messages", False),
+        (False, "values", True),
+        (True, "values", False),
+    ],
+)
+def test_graph_error_handler_recovers_on_the_executor_path(
+    parallel: bool, stream_mode: str, subgraphs: bool
+) -> None:
+    class State(TypedDict):
+        x: str
+
+    def failing(state: State) -> State:
+        raise ValueError("boom")
+
+    def handler(state: State) -> Command:
+        return Command(update={"x": "handled"}, goto=END)
+
+    builder = (
+        StateGraph(State)
+        .add_node("failing", failing, error_handler=handler)
+        .add_edge(START, "failing")
+    )
+    if parallel:
+        builder.add_node("sibling", lambda state: {}).add_edge(START, "sibling")
+    graph = builder.compile()
+
+    chunks = list(
+        graph.stream(
+            {"x": ""}, stream_mode=[stream_mode, "values"], subgraphs=subgraphs
+        )
+    )
+
+    assert [c[-1] for c in chunks if c[-2] == "values"][-1] == {"x": "handled"}
+
+
 def test_graph_error_handler_failure_fails_run():
     class State(TypedDict):
         foo: str

libs/langgraph/uv.lock

@@ -1439,7 +1439,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.18"
 source = { editable = "." }
 dependencies = [
     { name = "langchain-core" },
@@ -1625,7 +1625,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },

libs/prebuilt/uv.lock

@@ -286,7 +286,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.18"
 source = { editable = "../langgraph" }
 dependencies = [
     { name = "langchain-core" },
@@ -370,7 +370,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },

libs/sdk-py/langgraph_sdk/__init__.py

@@ -5,7 +5,7 @@ from langgraph_sdk.encryption.types import DecryptResult, EncryptionContext
 from langgraph_sdk.priority import Priority
 from langgraph_sdk.priority.types import PriorityContext, PrioritySettings
 
-__version__ = "0.4.9"
+__version__ = "0.4.10"
 
 __all__ = [
     "Auth",

libs/sdk-py/uv.lock

@@ -301,7 +301,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.18"
 source = { editable = "../langgraph" }
 dependencies = [
     { name = "langchain-core" },
@@ -385,7 +385,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.3.0"
+version = "4.3.1"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },