feat(langgraph): add Runtime.on_exit for cleanup that runs however a run ends

Bumps langgraph from 1.2.18 to 1.2.19.

Includes:

- List a `ToolNode`'s tool names in its `get_graph()` node metadata
(#9449)
- Apply a node's `trace_policy` to tracers only, so it no longer changes
what streams see (#9486)
- Give `messages` and `tools` events the namespace of the graph they ran
in (#9458)
- Stream messages a node returns from a graph streamed inside another
node (#9463)
- Respect `subgraphs=False` in `RemoteGraph.stream` when the parent
streams subgraphs (#9453)
- Stop reporting a tool paused on `interrupt()` as failed on the `tools`
stream (#9406)
- Return an awaited `@task`'s value while streaming instead of `None`
(#9407)

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/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "langgraph-checkpoint-sqlite"
-version = "3.1.2"
+version = "3.1.3"
 description = "Library with a SQLite implementation of LangGraph checkpoint saver."
 authors = []
 requires-python = ">=3.10"
@@ -12,7 +12,7 @@ readme = "README.md"
 license = "MIT"
 license-files = ['LICENSE']
 dependencies = [
-    "langgraph-checkpoint>=4.3.0,<5.0.0",
+    "langgraph-checkpoint>=4.3.1,<5.0.0",
     "aiosqlite>=0.20",
     "sqlite-vec>=0.1.6",
 ]

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" },
@@ -360,7 +360,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint-sqlite"
-version = "3.1.2"
+version = "3.1.3"
 source = { editable = "." }
 dependencies = [
     { name = "aiosqlite" },

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/cli/js-monorepo-example/yarn.lock

@@ -2148,6 +2148,6 @@ yocto-queue@^0.1.0:
   integrity sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q==
 
 "zod@^3.25.76 || ^4":
-  version "4.3.6"
-  resolved "https://registry.yarnpkg.com/zod/-/zod-4.3.6.tgz#89c56e0aa7d2b05107d894412227087885ab112a"
-  integrity sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg==
+  version "4.6.7"
+  resolved "https://registry.yarnpkg.com/zod/-/zod-4.6.7.tgz#e806cf64a7f4e37635ce9f2f52c04c3766f75e5b"
+  integrity sha512-g8W2D2kU6a8untc053fX1uVBKzM7yqAxW/3zwk83+6RyF2+SKOuV+c0wBDhUwzV1PaGapmZH+rmcUzPf+3CGwg==

libs/cli/langgraph_cli/__init__.py

@@ -1 +1 @@
-__version__ = "0.4.39"
+__version__ = "0.4.40"

libs/cli/langgraph_cli/deploy.py

@@ -1061,6 +1061,8 @@ def _docker_config_for_token(registry_host: str, token: str, username: str):
 
 _UPLOAD_TIMEOUT_SECONDS = 300
 _BYTES_PER_MIB = 1_048_576
+# Byte range Cloud Storage signs into upload URLs, up to the 200 MB archive limit.
+_GCS_SIZE_RANGE = f"0,{200 * _BYTES_PER_MIB}"
 
 
 class _ProgressReader:
@@ -1086,12 +1088,24 @@ class _ProgressReader:
         return self._file_size
 
 
-def _upload_to_gcs(signed_url: str, file_path: str, file_size: int) -> None:
-    """Upload tarball to GCS via signed PUT URL with progress display."""
+def _upload_source_tarball(
+    signed_url: str,
+    file_path: str,
+    file_size: int,
+    upload_headers: dict[str, str] | None,
+) -> None:
+    """Upload tarball via signed PUT URL with progress display."""
     import urllib.error
     import urllib.request
 
     em = _get_emitter()
+    # Control planes that return no `upload_headers` sign for the Cloud Storage
+    # size range. Content-Type is a fallback: without one, urllib sends a form
+    # content type, which breaks signatures that cover it.
+    headers = {
+        "Content-Type": "application/gzip",
+        **(upload_headers or {"X-Goog-Content-Length-Range": _GCS_SIZE_RANGE}),
+    }
 
     with open(file_path, "rb") as f:
         reader = _ProgressReader(f, file_size, em)
@@ -1099,11 +1113,7 @@ def _upload_to_gcs(signed_url: str, file_path: str, file_size: int) -> None:
             signed_url,
             data=reader,
             method="PUT",
-            headers={
-                "Content-Type": "application/gzip",
-                "Content-Length": str(file_size),
-                "X-Goog-Content-Length-Range": "0,209715200",
-            },
+            headers={**headers, "Content-Length": str(file_size)},
         )
         try:
             urllib.request.urlopen(req, timeout=_UPLOAD_TIMEOUT_SECONDS)
@@ -1423,7 +1433,9 @@ def _run_remote_build(
         step += 1
 
         _log_deploy_step(step, "Uploading source")
-        _upload_to_gcs(signed_url, archive_path, file_size)
+        _upload_source_tarball(
+            signed_url, archive_path, file_size, upload_data.get("upload_headers")
+        )
     step += 1
 
     _log_deploy_step(step, "Triggering remote build")

libs/cli/langgraph_cli/host_backend.py

@@ -283,10 +283,13 @@ class HostBackendClient:
         )
 
     def request_upload_url(self, deployment_id: str) -> dict[str, Any]:
-        """Get a signed GCS URL for uploading the source tarball."""
+        """Get a signed URL for uploading the source tarball."""
+        # Tells the control plane this client sends the returned
+        # `upload_headers` with its upload, which some storage requires.
         return self._request(
             "POST",
             f"/v2/deployments/{deployment_id}/upload-url",
+            {"supports_upload_headers": True},
         )
 
     def update_deployment(

libs/cli/tests/unit_tests/cli/test_deploy_command.py

@@ -96,6 +96,7 @@ class ControlPlaneDouble:
     existing_deployments: list[dict] = field(default_factory=list)
     push_token_status: int = 200
     push_token_extra: dict = field(default_factory=dict)
+    upload_url_extra: dict = field(default_factory=dict)
     create_error: str | None = None
     listeners: list[dict] = field(default_factory=list)
     listeners_by_id: dict[str, dict] = field(default_factory=dict)
@@ -163,7 +164,12 @@ class ControlPlaneDouble:
             )
         if path.endswith("/upload-url"):
             return httpx.Response(
-                200, json={"upload_url": SIGNED_UPLOAD_URL, "object_path": OBJECT_PATH}
+                200,
+                json={
+                    "upload_url": SIGNED_UPLOAD_URL,
+                    "object_path": OBJECT_PATH,
+                    **self.upload_url_extra,
+                },
             )
         if method == "PATCH":
             return httpx.Response(200, json={"tenant_id": "tenant-1"})
@@ -280,7 +286,7 @@ class DeployProject:
     control_plane: ControlPlaneDouble
     docker: DockerDouble
     timeline: list[str]
-    uploads: list[tuple[str, str, int]]
+    uploads: list[tuple[str, str, int, dict[str, str] | None]]
 
     def run(self, *args: str, host_url: str = CONTROL_PLANE_URL) -> Result:
         return CliRunner().invoke(
@@ -317,16 +323,21 @@ def deploy_project(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> DeployPro
     timeline: list[str] = []
     control_plane = ControlPlaneDouble(timeline)
     docker = DockerDouble(timeline)
-    uploads: list[tuple[str, str, int]] = []
+    uploads: list[tuple[str, str, int, dict[str, str] | None]] = []
 
     @contextmanager
     def fake_create_archive(config_path: Path, config: dict) -> Iterator[tuple]:
         timeline.append("create_archive")
         yield ARCHIVE
 
-    def fake_upload(signed_url: str, file_path: str, file_size: int) -> None:
+    def fake_upload(
+        signed_url: str,
+        file_path: str,
+        file_size: int,
+        upload_headers: dict[str, str] | None,
+    ) -> None:
         timeline.append("upload_archive")
-        uploads.append((signed_url, file_path, file_size))
+        uploads.append((signed_url, file_path, file_size, upload_headers))
 
     monkeypatch.setattr(deploy_module, "_no_input", False)
     monkeypatch.setattr(deploy_module, "_emitter", None)
@@ -344,7 +355,7 @@ def deploy_project(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> DeployPro
     )
     monkeypatch.setattr(deploy_module.platform, "machine", lambda: "x86_64")
     monkeypatch.setattr(archive_module, "create_archive", fake_create_archive)
-    monkeypatch.setattr(deploy_module, "_upload_to_gcs", fake_upload)
+    monkeypatch.setattr(deploy_module, "_upload_source_tarball", fake_upload)
     return DeployProject(control_plane, docker, timeline, uploads)
 
 
@@ -703,6 +714,9 @@ def test_deployment_not_created_by_the_cli_gets_an_actionable_error(
 def test_remote_build_creates_an_internal_source_deployment_and_uploads_the_archive(
     deploy_project: DeployProject,
 ) -> None:
+    upload_headers = {"Content-Type": "application/gzip", "x-ms-blob-type": "BlockBlob"}
+    deploy_project.control_plane.upload_url_extra = {"upload_headers": upload_headers}
+
     result = deploy_project.run("--remote", "--install-command", "yarn install")
 
     assert result.exit_code == 0, result.output
@@ -717,7 +731,12 @@ def test_remote_build_creates_an_internal_source_deployment_and_uploads_the_arch
     assert deploy_project.control_plane.bodies[CREATE_DEPLOYMENT]["source"] == (
         "internal_source"
     )
-    assert deploy_project.uploads == [(SIGNED_UPLOAD_URL, ARCHIVE[0], ARCHIVE[1])]
+    assert deploy_project.control_plane.bodies[_upload_url(CREATED_ID)] == {
+        "supports_upload_headers": True
+    }
+    assert deploy_project.uploads == [
+        (SIGNED_UPLOAD_URL, ARCHIVE[0], ARCHIVE[1], upload_headers)
+    ]
     assert deploy_project.control_plane.bodies[_patch(CREATED_ID)] == {
         "revision_source": "internal_source",
         "source_revision_config": {

libs/cli/tests/unit_tests/test_deploy_helpers.py

@@ -1458,3 +1458,59 @@ class TestPlacementOnAKnownListener:
     def test_refuses_and_names_the_namespaces(self, request_, listener, message):
         with pytest.raises(click.UsageError, match=message):
             request_.on(listener)
+
+
+DEFAULT_UPLOAD_HEADERS = {
+    "content-type": "application/gzip",
+    "content-length": "7",
+    "x-goog-content-length-range": "0,209715200",
+}
+
+
+@pytest.mark.parametrize(
+    ("upload_headers", "expected"),
+    [
+        pytest.param(None, DEFAULT_UPLOAD_HEADERS, id="missing_sends_defaults"),
+        pytest.param({}, DEFAULT_UPLOAD_HEADERS, id="empty_sends_defaults"),
+        pytest.param(
+            {
+                "content-type": "application/x-gzip",
+                "x-ms-blob-type": "BlockBlob",
+                "content-length": "1",
+            },
+            {
+                "content-type": "application/x-gzip",
+                "x-ms-blob-type": "BlockBlob",
+                "content-length": "7",
+            },
+            id="returned_headers_replace_defaults",
+        ),
+        pytest.param(
+            {"x-ms-blob-type": "BlockBlob"},
+            {
+                "content-type": "application/gzip",
+                "x-ms-blob-type": "BlockBlob",
+                "content-length": "7",
+            },
+            id="returned_headers_keep_a_content_type",
+        ),
+    ],
+)
+def test_source_upload_sends_the_headers_the_signed_url_requires(
+    tmp_path, mocker, upload_headers, expected
+):
+    archive = tmp_path / "source.tar.gz"
+    archive.write_bytes(b"tarball")
+    sent = []
+    mocker.patch(
+        "langgraph_cli.deploy._get_emitter", return_value=MagicMock(json_mode=True)
+    )
+    mocker.patch(
+        "urllib.request.urlopen", side_effect=lambda req, timeout: sent.append(req)
+    )
+
+    deploy_mod._upload_source_tarball(
+        "https://storage.example/signed", str(archive), 7, upload_headers
+    )
+
+    assert {name.lower(): value for name, value in sent[0].header_items()} == expected

libs/langgraph/langgraph/_internal/_runnable.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import copy
 import enum
 import inspect
 import logging
@@ -23,9 +24,16 @@ from typing import (
     Optional,
     Protocol,
     TypeGuard,
+    TypeVar,
     cast,
 )
 
+from langchain_core.callbacks.base import BaseCallbackHandler, BaseCallbackManager
+from langchain_core.callbacks.manager import (
+    AsyncCallbackManagerForChainRun,
+    BaseRunManager,
+    CallbackManagerForChainRun,
+)
 from langchain_core.runnables.base import (
     Runnable,
     RunnableConfig,
@@ -41,6 +49,7 @@ from langchain_core.runnables.config import (
     var_child_runnable_config,
 )
 from langchain_core.runnables.utils import Input, Output
+from langchain_core.tracers.base import BaseTracer
 from langchain_core.tracers.langchain import LangChainTracer
 from langgraph.store.base import BaseStore
 
@@ -57,7 +66,7 @@ from langgraph._internal._constants import (
 )
 from langgraph._internal._typing import MISSING
 from langgraph.errors import NodeError
-from langgraph.types import StreamWriter
+from langgraph.types import StreamWriter, TracePolicy
 
 try:
     from langchain_core.tracers._streaming import _StreamingCallbackHandler
@@ -85,6 +94,29 @@ def _trace_payload(value: Any, transform: Callable[[Any], Any] | None) -> Any:
         return value
 
 
+def _is_stream_handler(handler: BaseCallbackHandler) -> bool:
+    # Inheritance, not isinstance on the runtime-checkable protocol, which also
+    # matches any exporter that merely has the tap methods: stream handlers get a
+    # node's real payload and its streamed output.
+    return _StreamingCallbackHandler in type(handler).__mro__
+
+
+_M = TypeVar("_M", bound=BaseCallbackManager | BaseRunManager)
+
+
+def _split_handlers(manager: _M) -> tuple[_M, _M]:
+    # The recorded payload exists to keep tracer ingest small, so only tracers get it.
+    # `astream_log`'s handler is a tracer too, but it feeds the caller's own stream.
+    real, tracers = copy.copy(manager), copy.copy(manager)
+    tracers.handlers = [
+        h
+        for h in manager.handlers
+        if isinstance(h, BaseTracer) and not _is_stream_handler(h)
+    ]
+    real.handlers = [h for h in manager.handlers if h not in tracers.handlers]
+    return real, tracers
+
+
 def _set_config_context(
     config: RunnableConfig, run: Any = None
 ) -> Token[RunnableConfig | None]:
@@ -593,13 +625,15 @@ class RunnableSeq(Runnable):
         *steps: RunnableLike,
         name: str | None = None,
         trace_inputs: Callable[[Any], Any] | None = None,
-        trace_outputs: Callable[[Any], Any] | None = None,
+        trace_policy: TracePolicy | None = None,
     ) -> None:
         """Create a new RunnableSeq.
 
         Args:
             steps: The steps to include in the sequence.
             name: The name of the `Runnable`.
+            trace_inputs: Transforms the input every callback handler receives.
+            trace_policy: Processes what tracers record, after `trace_inputs`.
 
         Raises:
             ValueError: If the sequence has less than 2 steps.
@@ -619,7 +653,67 @@ class RunnableSeq(Runnable):
         self.steps = steps_flat
         self.name = name
         self.trace_inputs = trace_inputs
-        self.trace_outputs = trace_outputs
+        self.trace_policy = trace_policy or TracePolicy()
+
+    def _start(self, input: Any, config: RunnableConfig) -> CallbackManagerForChainRun:
+        callback_manager = get_callback_manager_for_config(config)
+        payload = _trace_payload(input, self.trace_inputs)
+        recorded = _trace_payload(payload, self.trace_policy.process_inputs)
+        name = config.get("run_name") or self.get_name()
+        run_id = config.pop("run_id", None)
+        if recorded is payload:
+            return callback_manager.on_chain_start(
+                None, payload, name=name, run_id=run_id
+            )
+        real, tracers = _split_handlers(callback_manager)
+        run_manager = real.on_chain_start(None, payload, name=name, run_id=run_id)
+        tracers.on_chain_start(None, recorded, name=name, run_id=run_manager.run_id)
+        run_manager.handlers = callback_manager.handlers
+        return run_manager
+
+    async def _astart(
+        self, input: Any, config: RunnableConfig
+    ) -> AsyncCallbackManagerForChainRun:
+        callback_manager = get_async_callback_manager_for_config(config)
+        payload = _trace_payload(input, self.trace_inputs)
+        recorded = _trace_payload(payload, self.trace_policy.process_inputs)
+        name = config.get("run_name") or self.get_name()
+        run_id = config.pop("run_id", None)
+        if recorded is payload:
+            return await callback_manager.on_chain_start(
+                None, payload, name=name, run_id=run_id
+            )
+        real, tracers = _split_handlers(callback_manager)
+        # Tracers start last, so a cancellation before then leaves no tracer run open.
+        run_manager = await real.on_chain_start(None, payload, name=name, run_id=run_id)
+        await tracers.on_chain_start(
+            None, recorded, name=name, run_id=run_manager.run_id
+        )
+        run_manager.handlers = callback_manager.handlers
+        return run_manager
+
+    def _end(self, run_manager: CallbackManagerForChainRun, output: Any) -> None:
+        recorded = _trace_payload(output, self.trace_policy.process_outputs)
+        if recorded is output:
+            run_manager.on_chain_end(output)
+        else:
+            real, tracers = _split_handlers(run_manager)
+            tracers.on_chain_end(recorded)
+            real.on_chain_end(output)
+
+    async def _aend(
+        self, run_manager: AsyncCallbackManagerForChainRun, output: Any
+    ) -> None:
+        recorded = _trace_payload(output, self.trace_policy.process_outputs)
+        if recorded is output:
+            await run_manager.on_chain_end(output)
+        else:
+            real, tracers = _split_handlers(run_manager)
+            # Tracers end first: on_chain_end is shielded once it starts, so a
+            # cancellation can only skip the other handlers' end, never leave a
+            # tracer run open.
+            await tracers.on_chain_end(recorded)
+            await real.on_chain_end(output)
 
     def __or__(
         self,
@@ -676,15 +770,8 @@ class RunnableSeq(Runnable):
     ) -> Any:
         if config is None:
             config = ensure_config()
-        # setup callbacks and context
-        callback_manager = get_callback_manager_for_config(config)
         # start the root run
-        run_manager = callback_manager.on_chain_start(
-            None,
-            _trace_payload(input, self.trace_inputs),
-            name=config.get("run_name") or self.get_name(),
-            run_id=config.pop("run_id", None),
-        )
+        run_manager = self._start(input, config)
         # invoke all steps in sequence
         try:
             for i, step in enumerate(self.steps):
@@ -712,7 +799,7 @@ class RunnableSeq(Runnable):
             run_manager.on_chain_error(e)
             raise
         else:
-            run_manager.on_chain_end(_trace_payload(input, self.trace_outputs))
+            self._end(run_manager, input)
             return input
 
     async def ainvoke(
@@ -723,15 +810,8 @@ class RunnableSeq(Runnable):
     ) -> Any:
         if config is None:
             config = ensure_config()
-        # setup callbacks
-        callback_manager = get_async_callback_manager_for_config(config)
         # start the root run
-        run_manager = await callback_manager.on_chain_start(
-            None,
-            _trace_payload(input, self.trace_inputs),
-            name=config.get("run_name") or self.get_name(),
-            run_id=config.pop("run_id", None),
-        )
+        run_manager = await self._astart(input, config)
 
         # invoke all steps in sequence
         try:
@@ -765,7 +845,7 @@ class RunnableSeq(Runnable):
             await run_manager.on_chain_error(e)
             raise
         else:
-            await run_manager.on_chain_end(_trace_payload(input, self.trace_outputs))
+            await self._aend(run_manager, input)
             return input
 
     def stream(
@@ -776,15 +856,8 @@ class RunnableSeq(Runnable):
     ) -> Iterator[Any]:
         if config is None:
             config = ensure_config()
-        # setup callbacks
-        callback_manager = get_callback_manager_for_config(config)
         # start the root run
-        run_manager = callback_manager.on_chain_start(
-            None,
-            _trace_payload(input, self.trace_inputs),
-            name=config.get("run_name") or self.get_name(),
-            run_id=config.pop("run_id", None),
-        )
+        run_manager = self._start(input, config)
         # get the run object
         for h in run_manager.handlers:
             if isinstance(h, LangChainTracer):
@@ -814,10 +887,9 @@ class RunnableSeq(Runnable):
                         )
                         iterator = step.transform(iterator, config)
                 # populates streamed_output in astream_log() output if needed
-                if _StreamingCallbackHandler is not None:
-                    for h in run_manager.handlers:
-                        if isinstance(h, _StreamingCallbackHandler):
-                            iterator = h.tap_output_iter(run_manager.run_id, iterator)
+                for h in run_manager.handlers:
+                    if _is_stream_handler(h):
+                        iterator = h.tap_output_iter(run_manager.run_id, iterator)
                 # consume into final output
                 output = context.run(_consume_iter, iterator)
                 # sequence doesn't emit output, yield to mark as generator
@@ -826,7 +898,7 @@ class RunnableSeq(Runnable):
                 run_manager.on_chain_error(e)
                 raise
             else:
-                run_manager.on_chain_end(_trace_payload(output, self.trace_outputs))
+                self._end(run_manager, output)
 
     async def astream(
         self,
@@ -836,15 +908,8 @@ class RunnableSeq(Runnable):
     ) -> AsyncIterator[Any]:
         if config is None:
             config = ensure_config()
-        # setup callbacks
-        callback_manager = get_async_callback_manager_for_config(config)
         # start the root run
-        run_manager = await callback_manager.on_chain_start(
-            None,
-            _trace_payload(input, self.trace_inputs),
-            name=config.get("run_name") or self.get_name(),
-            run_id=config.pop("run_id", None),
-        )
+        run_manager = await self._astart(input, config)
         # stream the last steps
         # transform the input stream of each step with the next
         # steps that don't natively support transforming an input stream will
@@ -880,12 +945,11 @@ class RunnableSeq(Runnable):
                             if hasattr(aiterator, "aclose"):
                                 stack.push_async_callback(aiterator.aclose)
                         # populates streamed_output in astream_log() output if needed
-                        if _StreamingCallbackHandler is not None:
-                            for h in run_manager.handlers:
-                                if isinstance(h, _StreamingCallbackHandler):
-                                    aiterator = h.tap_output_aiter(
-                                        run_manager.run_id, aiterator
-                                    )
+                        for h in run_manager.handlers:
+                            if _is_stream_handler(h):
+                                aiterator = h.tap_output_aiter(
+                                    run_manager.run_id, aiterator
+                                )
                         # consume into final output
                         output = await asyncio.create_task(
                             _consume_aiter(aiterator), context=context
@@ -896,9 +960,7 @@ class RunnableSeq(Runnable):
                     await run_manager.on_chain_error(e)
                     raise
                 else:
-                    await run_manager.on_chain_end(
-                        _trace_payload(output, self.trace_outputs)
-                    )
+                    await self._aend(run_manager, output)
         else:
             try:
                 async with AsyncExitStack() as stack:
@@ -914,12 +976,11 @@ class RunnableSeq(Runnable):
                         if hasattr(aiterator, "aclose"):
                             stack.push_async_callback(aiterator.aclose)
                     # populates streamed_output in astream_log() output if needed
-                    if _StreamingCallbackHandler is not None:
-                        for h in run_manager.handlers:
-                            if isinstance(h, _StreamingCallbackHandler):
-                                aiterator = h.tap_output_aiter(
-                                    run_manager.run_id, aiterator
-                                )
+                    for h in run_manager.handlers:
+                        if _is_stream_handler(h):
+                            aiterator = h.tap_output_aiter(
+                                run_manager.run_id, aiterator
+                            )
                     # consume into final output
                     output = await _consume_aiter(aiterator)
                     # sequence doesn't emit output, yield to mark as generator
@@ -928,9 +989,7 @@ class RunnableSeq(Runnable):
                 await run_manager.on_chain_error(e)
                 raise
             else:
-                await run_manager.on_chain_end(
-                    _trace_payload(output, self.trace_outputs)
-                )
+                await self._aend(run_manager, output)
 
 
 def _consume_iter(it: Iterator[Any]) -> Any:

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/graph/message.py

@@ -22,7 +22,7 @@ from langchain_core.messages import (
 )
 from typing_extensions import TypedDict, deprecated
 
-from langgraph._internal._constants import CONF, CONFIG_KEY_SEND, NS_SEP
+from langgraph._internal._constants import CONF, CONFIG_KEY_SEND
 from langgraph.graph.state import StateGraph
 from langgraph.pregel._messages import (
     _messages_delta_reducer as _messages_delta_reducer,
@@ -343,7 +343,7 @@ def push_message(
     )
 
     from langgraph.config import get_config
-    from langgraph.pregel._messages import StreamMessagesHandler
+    from langgraph.pregel._messages import StreamMessagesHandler, graph_namespace
 
     config = get_config()
     message = next(x for x in convert_to_messages([message]))
@@ -359,15 +359,12 @@ def push_message(
     ):
         handlers = config["callbacks"]
 
-    if stream_handler := next(
-        (x for x in handlers if isinstance(x, StreamMessagesHandler)), None
-    ):
-        metadata = config["metadata"]
-        message_meta = (
-            tuple(cast(str, metadata["langgraph_checkpoint_ns"]).split(NS_SEP)),
-            metadata,
-        )
-        stream_handler._emit(message_meta, message, dedupe=False)
+    metadata = config["metadata"]
+    for handler in handlers:
+        if isinstance(handler, StreamMessagesHandler):
+            ns = graph_namespace(metadata)
+            if handler.subgraphs or not ns or ns == handler.parent_ns:
+                handler._emit((ns, metadata), message, dedupe=False)
 
     if state_key:
         config[CONF][CONFIG_KEY_SEND]([(state_key, message)])

libs/langgraph/langgraph/pregel/_draw.py

@@ -228,6 +228,10 @@ def draw_graph(
             metadata["__interrupt"] = "before"
         elif name in interrupt_after_nodes:
             metadata["__interrupt"] = "after"
+        # Duck-typed so core doesn't import ToolNode from langgraph-prebuilt.
+        tools_by_name = getattr(node.bound, "tools_by_name", None)
+        if isinstance(tools_by_name, Mapping) and tools_by_name:
+            metadata["__tools"] = list(tools_by_name)
         graph.add_node(node.bound, name, metadata=metadata or None)
     # add start node
     if START not in nodes:

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/_loop.py

@@ -132,7 +132,7 @@ from langgraph.pregel.debug import (
     map_debug_tasks,
 )
 from langgraph.pregel.protocol import StreamChunk, StreamProtocol
-from langgraph.runtime import RunControl, Runtime
+from langgraph.runtime import RunControl, Runtime, _RunExits
 from langgraph.types import (
     All,
     CachePolicy,
@@ -1497,6 +1497,10 @@ class PregelLoop:
             if self._delta_write_futs is not None:
                 self._delta_write_futs.append(fut)
 
+    def _run_exits(self) -> _RunExits | None:
+        runtime = self.config[CONF].get(CONFIG_KEY_RUNTIME)
+        return runtime._run_exits if isinstance(runtime, Runtime) else None
+
     def _suppress_interrupt(
         self,
         exc_type: type[BaseException] | None,
@@ -1874,6 +1878,10 @@ class SyncPregelLoop(PregelLoop, AbstractContextManager):
         self._exit_delta_writes = (
             [] if self.durability == "exit" and self.checkpointer is not None else None
         )
+        # Bottom of the stack, so run-exit callbacks run last: after the
+        # executor has stopped every task and the final checkpoint is saved.
+        if (exits := self._run_exits()) is not None and exits.bind(is_async=False):
+            self.stack.push(exits.exit)
         self.submit = self.stack.enter_context(BackgroundExecutor(self.config))
         self.channels, self.managed = channels_from_checkpoint(
             self.specs,
@@ -2130,6 +2138,10 @@ class AsyncPregelLoop(PregelLoop, AbstractAsyncContextManager):
         self._exit_delta_writes = (
             [] if self.durability == "exit" and self.checkpointer is not None else None
         )
+        # Bottom of the stack, so run-exit callbacks run last: after the
+        # executor has stopped every task and the final checkpoint is saved.
+        if (exits := self._run_exits()) is not None and exits.bind(is_async=True):
+            self.stack.push_async_exit(exits.aexit)
         self.submit = await self.stack.enter_async_context(
             AsyncBackgroundExecutor(self.config)
         )

libs/langgraph/langgraph/pregel/_messages.py

@@ -23,7 +23,7 @@ from langchain_core.outputs import ChatGeneration, ChatGenerationChunk, LLMResul
 from pydantic import BaseModel
 
 from langgraph._internal._config import filter_to_user_tags
-from langgraph._internal._constants import NS_SEP
+from langgraph._internal._constants import NS_SEP, PUSH
 from langgraph.channels.binop import _get_overwrite
 from langgraph.channels.delta import DeltaChannel
 from langgraph.constants import TAG_HIDDEN, TAG_NOSTREAM
@@ -55,6 +55,23 @@ def _state_values(obj: Any) -> Sequence[Any]:
     return ()
 
 
+def graph_namespace(metadata: Mapping[str, Any]) -> tuple[str, ...]:
+    """Namespace of the graph a task runs in, from the task's run metadata.
+
+    Drops the task's own segment, plus one per enclosing `@task` call: a call
+    runs in its caller's graph but nests its segment under the caller's. A
+    call's `langgraph_path` is `(PUSH, <caller's path>, <index>, True)`, while
+    a `Send` task's ends in `False`.
+    """
+    ns = tuple(cast(str, metadata["langgraph_checkpoint_ns"]).split(NS_SEP))
+    path = metadata.get("langgraph_path", ())
+    drop = 1
+    while len(path) == 4 and path[0] == PUSH and path[-1] is True:
+        drop += 1
+        path = path[1]
+    return ns[:-drop]
+
+
 class StreamMessagesHandler(BaseCallbackHandler, _StreamingCallbackHandler):
     """A callback handler that implements stream_mode=messages.
 
@@ -148,9 +165,7 @@ class StreamMessagesHandler(BaseCallbackHandler, _StreamingCallbackHandler):
         **kwargs: Any,
     ) -> Any:
         if metadata and (not tags or (TAG_NOSTREAM not in tags)):
-            ns = tuple(cast(str, metadata["langgraph_checkpoint_ns"]).split(NS_SEP))[
-                :-1
-            ]
+            ns = graph_namespace(metadata)
             if not self.subgraphs and len(ns) > 0 and ns != self.parent_ns:
                 return
             if (filtered_tags := filter_to_user_tags(tags)) is not None:
@@ -213,10 +228,8 @@ class StreamMessagesHandler(BaseCallbackHandler, _StreamingCallbackHandler):
             and kwargs.get("name") == metadata.get("langgraph_node")
             and (not tags or TAG_HIDDEN not in tags)
         ):
-            ns = tuple(cast(str, metadata["langgraph_checkpoint_ns"]).split(NS_SEP))[
-                :-1
-            ]
-            if not self.subgraphs and len(ns) > 0:
+            ns = graph_namespace(metadata)
+            if not self.subgraphs and len(ns) > 0 and ns != self.parent_ns:
                 return
             self.metadata[run_id] = (ns, metadata)
             for value in _state_values(inputs):

libs/langgraph/langgraph/pregel/_read.py

@@ -227,23 +227,14 @@ class PregelNode:
     def node(self) -> Runnable[Any, Any] | None:
         """Get a runnable that combines `bound` and `writers`."""
         writers = self.flat_writers
-        trace_inputs = self.trace_policy.process_inputs if self.trace_policy else None
-        trace_outputs = self.trace_policy.process_outputs if self.trace_policy else None
         if self.bound is DEFAULT_BOUND and not writers:
             return None
         elif self.bound is DEFAULT_BOUND and len(writers) == 1:
             return writers[0]
         elif self.bound is DEFAULT_BOUND:
-            return RunnableSeq(
-                *writers, trace_inputs=trace_inputs, trace_outputs=trace_outputs
-            )
+            return RunnableSeq(*writers, trace_policy=self.trace_policy)
         elif writers:
-            return RunnableSeq(
-                self.bound,
-                *writers,
-                trace_inputs=trace_inputs,
-                trace_outputs=trace_outputs,
-            )
+            return RunnableSeq(self.bound, *writers, trace_policy=self.trace_policy)
         else:
             return self.bound
 

libs/langgraph/langgraph/pregel/_retry.py

@@ -34,6 +34,7 @@ from langgraph._internal._constants import (
     CONFIG_KEY_THREAD_ID,
     CONFIG_KEY_TIMED_ATTEMPT_OBSERVER,
     NS_SEP,
+    RETURN,
 )
 from langgraph._internal._runnable import create_task_in_config_context
 from langgraph._internal._timeout import sync_timeout_unsupported
@@ -733,15 +734,14 @@ async def arun_with_retry(
                 if stream:
                     async for _ in task.proc.astream(task.input, config):
                         pass
-                    break
+                    return _return_value(task)
                 return await task.proc.ainvoke(task.input, config)
             result = await _arun_with_timeout(
                 task, config, resolved_timeout, attempt_ctx, stream=stream
             )
             _finish_timed_attempt(config, attempt_ctx)
             if stream:
-                # if successful, end
-                break
+                return _return_value(task)
             return result
         except ParentCommand as exc:
             ns: str = config[CONF][CONFIG_KEY_CHECKPOINT_NS]
@@ -831,6 +831,12 @@ async def arun_with_retry(
             config = patch_configurable(config, {CONFIG_KEY_RESUMING: True})
 
 
+def _return_value(task: PregelExecutableTask) -> Any:
+    # Streaming drains the task instead of returning its result, so a caller
+    # awaiting a `@task` needs the value the task wrote.
+    return next((value for channel, value in task.writes if channel == RETURN), None)
+
+
 def _should_retry_on(retry_policy: RetryPolicy, exc: Exception) -> bool:
     """Check if the given exception should be retried based on the retry policy."""
     if isinstance(retry_policy.retry_on, Sequence):

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/langgraph/pregel/_tools.py

@@ -7,8 +7,9 @@ from uuid import UUID
 
 from langchain_core.callbacks import BaseCallbackHandler
 
-from langgraph._internal._constants import NS_SEP
 from langgraph.constants import TAG_NOSTREAM
+from langgraph.errors import GraphDrained, GraphInterrupt
+from langgraph.pregel._messages import graph_namespace
 from langgraph.pregel.protocol import StreamChunk
 
 try:
@@ -91,12 +92,9 @@ class StreamToolCallHandler(BaseCallbackHandler, _StreamingCallbackHandler):
     ) -> tuple[str, ...] | None:
         """Resolve the namespace this tool call should emit at, or `None` to skip.
 
-        Mirrors `StreamMessagesHandler.on_chat_model_start`'s namespace
-        derivation: parses `langgraph_checkpoint_ns` (which ends with
-        the `node_name:task_id` of the calling node), drops that
-        trailing segment, and returns the containing subgraph's own
-        namespace. Returns `None` when the call should be silently
-        suppressed:
+        Mirrors `StreamMessagesHandler.on_chat_model_start`: the namespace
+        is that of the graph the tool runs in (`graph_namespace`). Returns
+        `None` when the call should be silently suppressed:
 
         - `metadata` is missing — handler is attached to a context
           without Pregel routing info.
@@ -109,11 +107,9 @@ class StreamToolCallHandler(BaseCallbackHandler, _StreamingCallbackHandler):
             return None
         if tags and TAG_NOSTREAM in tags:
             return None
-        nskey = metadata.get("langgraph_checkpoint_ns")
-        if not nskey:
-            ns: tuple[str, ...] = ()
-        else:
-            ns = tuple(cast(str, nskey).split(NS_SEP))[:-1]
+        ns = (
+            graph_namespace(metadata) if metadata.get("langgraph_checkpoint_ns") else ()
+        )
         if not self.subgraphs and len(ns) > 0 and ns != self.parent_ns:
             return None
         return ns
@@ -188,6 +184,10 @@ class StreamToolCallHandler(BaseCallbackHandler, _StreamingCallbackHandler):
             return
         ns, tool_call_id, token = info
         self._reset_writer(token)
+        # An interrupted or drained tool is paused, not failed: it runs again
+        # on resume and reports its start and end then.
+        if isinstance(error, (GraphInterrupt, GraphDrained)):
+            return
         self.stream(
             (
                 ns,

libs/langgraph/langgraph/pregel/main.py

@@ -97,6 +97,7 @@ from langgraph._internal._runnable import (
     Runnable,
     RunnableLike,
     RunnableSeq,
+    _is_stream_handler,
     coerce_to_runnable,
 )
 from langgraph._internal._timeout import coerce_timeout_policy
@@ -174,6 +175,7 @@ from langgraph.runtime import (
     RunControl,
     Runtime,
     ServerInfo,
+    _RunExits,
 )
 from langgraph.stream._mux import StreamMux
 from langgraph.stream._types import StreamTransformer
@@ -203,11 +205,6 @@ from langgraph.types import (
 from langgraph.typing import ContextT, InputT, OutputT, StateT
 from langgraph.warnings import LangGraphDeprecatedSinceV10
 
-try:
-    from langchain_core.tracers._streaming import _StreamingCallbackHandler
-except ImportError:
-    _StreamingCallbackHandler = None  # type: ignore
-
 __all__ = ("NodeBuilder", "Pregel")
 
 _WriteValue = Callable[[Input], Output] | Any
@@ -2880,6 +2877,20 @@ class Pregel(
                     for h in callback_manager.inheritable_handlers
                     if not isinstance(h, StreamMessagesHandlerV2)
                 ]
+            if CONFIG_KEY_TASK_ID not in config[CONF]:
+                # Not run as a task (a child invoked with its own thread, say),
+                # this graph's namespace starts at the root, so a caller's
+                # handler would take this graph's events for its own graph's.
+                callback_manager.handlers = [
+                    h
+                    for h in callback_manager.handlers
+                    if not _is_stream_mode_handler(h)
+                ]
+                callback_manager.inheritable_handlers = [
+                    h
+                    for h in callback_manager.inheritable_handlers
+                    if not _is_stream_mode_handler(h)
+                ]
             if "ls_integration" not in callback_manager.metadata:
                 callback_manager.add_metadata({"ls_integration": "langgraph"})
             run_manager = callback_manager.on_chain_start(
@@ -2898,9 +2909,9 @@ class Pregel(
                 )
             # set up subgraph checkpointing
             config = self._own_checkpoint_config(config)
+            stream_handlers: list[StreamMessagesHandler | StreamToolCallHandler] = []
             # set up messages stream mode
             if "messages" in stream_modes:
-                ns_ = cast(str | None, config[CONF].get(CONFIG_KEY_CHECKPOINT_NS))
                 use_stream_messages_v2 = bool(
                     version == "v2" and config[CONF].get(CONFIG_KEY_STREAM_MESSAGES_V2)
                 )
@@ -2909,24 +2920,12 @@ class Pregel(
                     if use_stream_messages_v2
                     else StreamMessagesHandler
                 )
-                run_manager.inheritable_handlers.append(
-                    messages_handler_cls(
-                        stream.put,
-                        subgraphs,
-                        parent_ns=tuple(ns_.split(NS_SEP)) if ns_ else None,
-                    )
-                )
+                stream_handlers.append(messages_handler_cls(stream.put, subgraphs))
 
             # set up tools stream mode
             if "tools" in stream_modes:
-                ns_tools = cast(str | None, config[CONF].get(CONFIG_KEY_CHECKPOINT_NS))
-                run_manager.inheritable_handlers.append(
-                    StreamToolCallHandler(
-                        stream.put,
-                        subgraphs,
-                        parent_ns=tuple(ns_tools.split(NS_SEP)) if ns_tools else None,
-                    )
-                )
+                stream_handlers.append(StreamToolCallHandler(stream.put, subgraphs))
+            run_manager.inheritable_handlers.extend(stream_handlers)
 
             # set up custom stream mode
             if "custom" in stream_modes:
@@ -2968,6 +2967,8 @@ class Pregel(
                 execution_info=None,
                 server_info=server_info,
                 control=control or parent_runtime.control or RunControl(),
+                # a subgraph shares the root run's exit callbacks
+                _run_exits=parent_runtime._run_exits or _RunExits(),
             )
             runtime = parent_runtime.merge(runtime)
             config[CONF][CONFIG_KEY_RUNTIME] = runtime
@@ -3009,6 +3010,10 @@ class Pregel(
                 cache_policy=self.cache_policy,
                 has_graph_lifecycle_callbacks=bool(graph_callback_manager.handlers),
             ) as loop:
+                # Known only now: the loop numbers the namespace of every
+                # subgraph a task runs after its first.
+                for handler in stream_handlers:
+                    handler.parent_ns = loop.checkpoint_ns
                 emit_graph_lifecycle_events(loop)
                 # create runner
                 runner = PregelRunner(
@@ -3291,6 +3296,20 @@ class Pregel(
                     for h in callback_manager.inheritable_handlers
                     if not isinstance(h, StreamMessagesHandlerV2)
                 ]
+            if CONFIG_KEY_TASK_ID not in config[CONF]:
+                # Not run as a task (a child invoked with its own thread, say),
+                # this graph's namespace starts at the root, so a caller's
+                # handler would take this graph's events for its own graph's.
+                callback_manager.handlers = [
+                    h
+                    for h in callback_manager.handlers
+                    if not _is_stream_mode_handler(h)
+                ]
+                callback_manager.inheritable_handlers = [
+                    h
+                    for h in callback_manager.inheritable_handlers
+                    if not _is_stream_mode_handler(h)
+                ]
             if "ls_integration" not in callback_manager.metadata:
                 callback_manager.add_metadata({"ls_integration": "langgraph"})
             run_manager = await callback_manager.on_chain_start(
@@ -3304,18 +3323,10 @@ class Pregel(
                 run_id=run_manager.run_id,
             )
             # if running from astream_log() run each proc with streaming
-            do_stream = (
-                next(
-                    (
-                        True
-                        for h in run_manager.handlers
-                        if isinstance(h, _StreamingCallbackHandler)
-                        and not isinstance(h, StreamMessagesHandler)
-                    ),
-                    False,
-                )
-                if _StreamingCallbackHandler is not None
-                else False
+            do_stream = any(
+                _is_stream_handler(h)
+                and not isinstance(h, (StreamMessagesHandler, StreamToolCallHandler))
+                for h in run_manager.handlers
             )
             if checkpointer is None and durability is not None:
                 warnings.warn(
@@ -3323,10 +3334,9 @@ class Pregel(
                 )
             # set up subgraph checkpointing
             config = self._own_checkpoint_config(config)
+            stream_handlers: list[StreamMessagesHandler | StreamToolCallHandler] = []
             # set up messages stream mode
             if "messages" in stream_modes:
-                # namespace can be None in a root level graph?
-                ns_ = cast(str | None, config[CONF].get(CONFIG_KEY_CHECKPOINT_NS))
                 use_stream_messages_v2 = bool(
                     version == "v2" and config[CONF].get(CONFIG_KEY_STREAM_MESSAGES_V2)
                 )
@@ -3335,24 +3345,12 @@ class Pregel(
                     if use_stream_messages_v2
                     else StreamMessagesHandler
                 )
-                run_manager.inheritable_handlers.append(
-                    messages_handler_cls(
-                        stream_put,
-                        subgraphs,
-                        parent_ns=tuple(ns_.split(NS_SEP)) if ns_ else None,
-                    )
-                )
+                stream_handlers.append(messages_handler_cls(stream_put, subgraphs))
 
             # set up tools stream mode
             if "tools" in stream_modes:
-                ns_tools = cast(str | None, config[CONF].get(CONFIG_KEY_CHECKPOINT_NS))
-                run_manager.inheritable_handlers.append(
-                    StreamToolCallHandler(
-                        stream_put,
-                        subgraphs,
-                        parent_ns=tuple(ns_tools.split(NS_SEP)) if ns_tools else None,
-                    )
-                )
+                stream_handlers.append(StreamToolCallHandler(stream_put, subgraphs))
+            run_manager.inheritable_handlers.extend(stream_handlers)
 
             # set up custom stream mode
             def stream_writer(c: Any) -> None:
@@ -3409,6 +3407,8 @@ class Pregel(
                 execution_info=None,
                 server_info=server_info,
                 control=control or parent_runtime.control or RunControl(),
+                # a subgraph shares the root run's exit callbacks
+                _run_exits=parent_runtime._run_exits or _RunExits(),
             )
             runtime = parent_runtime.merge(runtime)
             config[CONF][CONFIG_KEY_RUNTIME] = runtime
@@ -3461,6 +3461,10 @@ class Pregel(
                 cache_policy=self.cache_policy,
                 has_graph_lifecycle_callbacks=bool(graph_callback_manager.handlers),
             ) as loop:
+                # Known only now: the loop numbers the namespace of every
+                # subgraph a task runs after its first.
+                for handler in stream_handlers:
+                    handler.parent_ns = loop.checkpoint_ns
                 await aemit_graph_lifecycle_events(loop)
                 # create runner
                 runner = PregelRunner(
@@ -4458,6 +4462,10 @@ def _coerce_checkpoint_values(payload: Any, mapper: Callable[[Any], Any]) -> Non
         payload["values"] = mapper(payload["values"])
 
 
+def _is_stream_mode_handler(handler: object) -> bool:
+    return isinstance(handler, (StreamMessagesHandler, StreamToolCallHandler))
+
+
 def _resolve_parent_ns(
     graph_config: RunnableConfig | None, call_config: RunnableConfig | None
 ) -> tuple[str, ...]:

libs/langgraph/langgraph/pregel/remote.py

@@ -847,6 +847,11 @@ class RemoteGraph(PregelProtocol):
             # filter for what was actually requested
             if mode not in requested:
                 continue
+            # subgraph events may have been requested only for the parent stream.
+            # messages are exempt: the server dedupes them across namespaces, so
+            # dropping them here would also drop the root-level message
+            if not subgraphs and NS_SEP in chunk.event and mode != "messages":
+                continue
 
             if chunk.event.startswith("messages"):
                 chunk = chunk._replace(data=tuple(chunk.data))
@@ -997,6 +1002,11 @@ class RemoteGraph(PregelProtocol):
             # filter for what was actually requested
             if mode not in requested:
                 continue
+            # subgraph events may have been requested only for the parent stream.
+            # messages are exempt: the server dedupes them across namespaces, so
+            # dropping them here would also drop the root-level message
+            if not subgraphs and NS_SEP in chunk.event and mode != "messages":
+                continue
 
             if chunk.event.startswith("messages"):
                 chunk = chunk._replace(data=tuple(chunk.data))

libs/langgraph/langgraph/runtime.py

@@ -1,7 +1,11 @@
 from __future__ import annotations
 
-from collections.abc import Callable
+import inspect
+import logging
+import threading
+from collections.abc import Awaitable, Callable
 from dataclasses import dataclass, field, replace
+from types import TracebackType
 from typing import Any, Generic, cast
 
 from langgraph.store.base import BaseStore
@@ -104,6 +108,129 @@ class RunControl:
         return self._drain_reason
 
 
+logger = logging.getLogger(__name__)
+
+ExitCallback = Callable[[], Awaitable[None] | None]
+"""A cleanup callback registered with `Runtime.on_exit`."""
+
+
+class _RunExits:
+    """Cleanup callbacks for one root graph invocation.
+
+    Created by the root `stream`/`astream` call and shared by every subgraph
+    it runs, through `Runtime`. The root Pregel loop binds it at the bottom of
+    its exit stack, so callbacks run after the loop has stopped every task,
+    persisted its final checkpoint and handled any interrupt, whatever the
+    reason the run ended.
+    """
+
+    __slots__ = ("_callbacks", "_is_async", "_lock", "_state")
+
+    def __init__(self) -> None:
+        self._callbacks: list[ExitCallback] = []
+        self._lock = threading.Lock()
+        self._is_async = False
+        # "new" -> "bound" (owned by a loop) -> "closed" (callbacks ran)
+        self._state = "new"
+
+    def bind(self, *, is_async: bool) -> bool:
+        """Claim these exits for a loop. Only the first (root) loop wins."""
+        with self._lock:
+            if self._state != "new":
+                return False
+            self._state = "bound"
+            self._is_async = is_async
+            return True
+
+    def register(self, callback: ExitCallback) -> None:
+        if not callable(callback):
+            msg = "on_exit() expects a callable"
+            raise TypeError(msg)
+        with self._lock:
+            if self._state == "closed":
+                msg = "on_exit() called after the graph run has already exited"
+                raise RuntimeError(msg)
+            if not self._is_async and _is_async_callable(callback):
+                msg = (
+                    "on_exit() got an async callback in a synchronous graph run "
+                    "(invoke/stream). Register a sync callback, or run the graph "
+                    "with ainvoke/astream."
+                )
+                raise TypeError(msg)
+            self._callbacks.append(callback)
+
+    def _drain(self) -> list[ExitCallback]:
+        with self._lock:
+            self._state = "closed"
+            callbacks = self._callbacks[::-1]  # LIFO
+            self._callbacks = []
+        return callbacks
+
+    def exit(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_value: BaseException | None,
+        traceback: TracebackType | None,
+    ) -> bool:
+        errors: list[Exception] = []
+        for callback in self._drain():
+            try:
+                result = callback()
+                if inspect.isawaitable(result):
+                    if inspect.iscoroutine(result):
+                        result.close()
+                    msg = (
+                        f"on_exit() callback {callback!r} returned an awaitable "
+                        "in a synchronous graph run; it was not awaited."
+                    )
+                    raise TypeError(msg)
+            except Exception as e:
+                errors.append(e)
+        return self._finish(errors, exc_value)
+
+    async def aexit(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_value: BaseException | None,
+        traceback: TracebackType | None,
+    ) -> bool:
+        errors: list[Exception] = []
+        for callback in self._drain():
+            try:
+                result = callback()
+                if inspect.isawaitable(result):
+                    await result
+            except Exception as e:
+                errors.append(e)
+        return self._finish(errors, exc_value)
+
+    @staticmethod
+    def _finish(errors: list[Exception], exc_value: BaseException | None) -> bool:
+        # Every callback runs even if an earlier one failed. A failing callback
+        # never replaces the run's own exception (error, cancellation, stream
+        # close): it is logged instead. If the run otherwise ended cleanly, the
+        # first callback error is raised so cleanup bugs aren't silent.
+        if not errors:
+            return False
+        if exc_value is None:
+            for e in errors[1:]:
+                logger.error("on_exit() callback failed", exc_info=e)
+            raise errors[0]
+        for e in errors:
+            logger.error(
+                "on_exit() callback failed while the graph run was exiting with %r",
+                exc_value,
+                exc_info=e,
+            )
+        return False
+
+
+def _is_async_callable(callback: Any) -> bool:
+    return inspect.iscoroutinefunction(callback) or inspect.iscoroutinefunction(
+        getattr(callback, "__call__", None)
+    )
+
+
 def _no_op_stream_writer(_: Any) -> None: ...
 
 
@@ -237,6 +364,40 @@ class Runtime(Generic[ContextT]):
     graph runtime.
     """
 
+    _run_exits: _RunExits | None = field(default=None, repr=False, compare=False)
+    """Exit callbacks of the root graph run. Use `on_exit` to register one."""
+
+    def on_exit(self, callback: ExitCallback) -> None:
+        """Register cleanup to run when the current graph run ends.
+
+        The callback runs once the root invocation (the `invoke`/`stream`/
+        `ainvoke`/`astream` call the caller made) exits for any reason: it
+        completed, raised, was cancelled, paused on an interrupt, or the caller
+        closed the stream or broke out of it. Calls from subgraphs register on
+        that same root run.
+
+        Callbacks take no arguments and run in reverse registration order,
+        after every task of the run has stopped and the final checkpoint has
+        been written. In `ainvoke`/`astream` a callback may be sync or async; in
+        `invoke`/`stream` it must be sync. A failing callback never hides the
+        run's own exception: it is logged, and raised only if the run otherwise
+        ended without one.
+
+        A process that is killed does not run its callbacks, so use them to
+        free resources early, not as the only guarantee they are freed.
+
+        Args:
+            callback: A zero-argument sync or async callable.
+
+        Raises:
+            RuntimeError: When called outside a graph run, or after it exited.
+            TypeError: When given an async callback in a synchronous run.
+        """
+        if self._run_exits is None:
+            msg = "on_exit() can only be called during a graph run"
+            raise RuntimeError(msg)
+        self._run_exits.register(callback)
+
     def merge(self, other: Runtime[ContextT]) -> Runtime[ContextT]:
         """Merge two runtimes together.
 
@@ -255,6 +416,7 @@ class Runtime(Generic[ContextT]):
             execution_info=other.execution_info or self.execution_info,
             server_info=other.server_info or self.server_info,
             control=other.control or self.control,
+            _run_exits=other._run_exits or self._run_exits,
         )
 
     def override(

libs/langgraph/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.19"
 description = "Building stateful, multi-actor applications with LLMs"
 authors = []
 requires-python = ">=3.10"

libs/langgraph/tests/__snapshots__/test_large_cases.ambr

@@ -133,6 +133,11 @@
             "ToolNode"
           ],
           "name": "tools"
+        },
+        "metadata": {
+          "__tools": [
+            "search_api"
+          ]
         }
       },
       {
@@ -221,6 +226,11 @@
             "ToolNode"
           ],
           "name": "tools"
+        },
+        "metadata": {
+          "__tools": [
+            "search_api"
+          ]
         }
       },
       {

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]
@@ -8931,6 +8950,39 @@ def test_subgraph_streaming_sync() -> None:
     assert result["num_chunks"] == 9
 
 
+def test_subgraph_streaming_node_output_messages_sync() -> None:
+    """Messages returned by a node (not streamed by an LLM) are emitted when a
+    graph is explicitly streamed with `stream_mode="messages"` inside a node."""
+
+    def respond(state: MessagesState) -> dict:
+        return {"messages": [AIMessage("hi there", id="ai1")]}
+
+    subgraph = (
+        StateGraph(MessagesState)
+        .add_node("respond", respond)
+        .add_edge(START, "respond")
+        .compile()
+    )
+    msgs = {"messages": [("user", "hello")]}
+
+    top_level = [msg for msg, _ in subgraph.stream(msgs, stream_mode="messages")]
+
+    def parent_node(state: MessagesState, config: RunnableConfig) -> dict:
+        nonlocal in_node
+        in_node = [
+            msg for msg, _ in subgraph.stream(msgs, config, stream_mode="messages")
+        ]
+        return {}
+
+    in_node: list = []
+    StateGraph(MessagesState).add_node("parent", parent_node).add_edge(
+        START, "parent"
+    ).compile().invoke(msgs)
+
+    assert [m.content for m in top_level] == ["hi there"]
+    assert [m.content for m in in_node] == ["hi there"]
+
+
 def test_get_graph_nonterminal_last_step_source(snapshot: SnapshotAssertion) -> None:
     class State(TypedDict):
         messages: list[str]

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]
@@ -6780,6 +6834,31 @@ async def test_multiple_updates() -> None:
     ]
 
 
+@NEEDS_CONTEXTVARS
+async def test_task_in_subgraph_node_returns_its_value_with_tools_mode() -> None:
+    class State(TypedDict):
+        out: int | None
+
+    @task
+    async def double(x: int) -> int:
+        return x * 2
+
+    async def node(state: State) -> State:
+        return {"out": await double(21)}
+
+    inner = StateGraph(State).add_node("node", node).add_edge(START, "node").compile()
+    graph = (
+        StateGraph(State).add_node("inner", inner).add_edge(START, "inner").compile()
+    )
+
+    chunks = [
+        chunk
+        async for chunk in graph.astream({"out": None}, stream_mode=["values", "tools"])
+    ]
+
+    assert chunks[-1] == ("values", {"out": 42})
+
+
 @NEEDS_CONTEXTVARS
 async def test_falsy_return_from_task(async_checkpointer: BaseCheckpointSaver) -> None:
     """Test with a falsy return from a task."""
@@ -7544,6 +7623,40 @@ async def test_entrypoint_from_async_generator() -> None:
             yield "b"
 
 
+@NEEDS_CONTEXTVARS
+@pytest.mark.parametrize("timeout", [None, 30])
+@pytest.mark.parametrize("version", ["v1", "v2"])
+async def test_awaited_task_returns_its_value_under_astream_events(
+    version: Literal["v1", "v2"], timeout: int | None
+) -> None:
+    class State(TypedDict):
+        doubled: int
+        zeroed: int
+
+    @task(timeout=timeout)
+    async def double(x: int) -> int:
+        return x * 2
+
+    @task(timeout=timeout)
+    async def zero() -> int:
+        return 0
+
+    async def node(state: State) -> State:
+        return {"doubled": await double(21), "zeroed": await zero()}
+
+    graph = StateGraph(State).add_node("node", node).add_edge(START, "node").compile()
+
+    outputs = [
+        event["data"]["output"]
+        async for event in graph.astream_events(
+            {"doubled": 0, "zeroed": 1}, version=version
+        )
+        if event["event"] == "on_chain_end" and event["name"] == "node"
+    ]
+
+    assert outputs == [{"doubled": 42, "zeroed": 0}]
+
+
 @NEEDS_CONTEXTVARS
 async def test_named_tasks_functional() -> None:
     class Foo:
@@ -9390,6 +9503,44 @@ async def test_subgraph_streaming_async() -> None:
     assert result["num_chunks"] == 9
 
 
+async def test_subgraph_streaming_node_output_messages_async() -> None:
+    """Messages returned by a node (not streamed by an LLM) are emitted when a
+    graph is explicitly streamed with `stream_mode="messages"` inside a node."""
+
+    async def respond(state: MessagesState) -> dict:
+        return {"messages": [AIMessage("hi there", id="ai1")]}
+
+    subgraph = (
+        StateGraph(MessagesState)
+        .add_node("respond", respond)
+        .add_edge(START, "respond")
+        .compile()
+    )
+    msgs = {"messages": [("user", "hello")]}
+
+    top_level = [msg async for msg, _ in subgraph.astream(msgs, stream_mode="messages")]
+
+    async def parent_node(state: MessagesState, config: RunnableConfig) -> dict:
+        nonlocal in_node
+        in_node = [
+            msg
+            async for msg, _ in subgraph.astream(msgs, config, stream_mode="messages")
+        ]
+        return {}
+
+    in_node: list = []
+    await (
+        StateGraph(MessagesState)
+        .add_node("parent", parent_node)
+        .add_edge(START, "parent")
+        .compile()
+        .ainvoke(msgs)
+    )
+
+    assert [m.content for m in top_level] == ["hi there"]
+    assert [m.content for m in in_node] == ["hi there"]
+
+
 @NEEDS_CONTEXTVARS
 async def test_null_resume_disallowed_with_multiple_interrupts(
     async_checkpointer: BaseCheckpointSaver,

libs/langgraph/tests/test_remote_graph.py

@@ -16,9 +16,11 @@ from langgraph_sdk.schema import StreamPart
 from pydantic import BaseModel
 from typing_extensions import TypedDict
 
+from langgraph._internal._constants import CONFIG_KEY_STREAM
 from langgraph.errors import GraphInterrupt
 from langgraph.graph import END, START, MessagesState, StateGraph, add_messages
 from langgraph.pregel import Pregel
+from langgraph.pregel.protocol import StreamProtocol
 from langgraph.pregel.remote import RemoteGraph
 from langgraph.types import Interrupt, StateSnapshot
 from tests.any_str import AnyStr
@@ -863,6 +865,87 @@ async def test_astream_subgraphs_keeps_caller_namespace():
     assert stream_parts == _CALLER_PREFIXED
 
 
+# Subgraph events requested only on behalf of a streaming parent graph
+_PARENT_STREAMED_PARTS = [
+    StreamPart(event="updates|sub:abc", data={"inner": {"chunk": "inner"}}),
+    StreamPart(event="messages|sub:abc", data=[{"content": "token"}, {}]),
+    StreamPart(event="updates", data={"sub": {"chunk": "root"}}),
+]
+
+
+def _parent_streamed_config(parent_parts: list) -> RunnableConfig:
+    return {
+        "configurable": {
+            "thread_id": "thread_1",
+            "checkpoint_ns": "outer:123",
+            CONFIG_KEY_STREAM: StreamProtocol(
+                parent_parts.append, {"updates", "messages"}
+            ),
+        }
+    }
+
+
+def test_stream_without_subgraphs_skips_parent_requested_subgraph_events():
+    mock_sync_client = MagicMock()
+    mock_sync_client.runs.stream.return_value = _PARENT_STREAMED_PARTS
+    remote_pregel = RemoteGraph("test_graph_id", sync_client=mock_sync_client)
+
+    for stream_mode, expected in [
+        ("updates", [{"sub": {"chunk": "root"}}]),
+        # messages are not filtered: the server dedupes them across namespaces
+        ("messages", [({"content": "token"}, {})]),
+    ]:
+        parent_parts: list = []
+        stream_parts = list(
+            remote_pregel.stream(
+                {"input": "data"},
+                _parent_streamed_config(parent_parts),
+                stream_mode=stream_mode,
+            )
+        )
+
+        assert stream_parts == expected
+        # subgraph events are still requested and forwarded to the parent
+        assert mock_sync_client.runs.stream.call_args.kwargs["stream_subgraphs"]
+        assert [ns for ns, _, _ in parent_parts] == [
+            ("outer:123", "sub:abc"),
+            ("outer:123", "sub:abc"),
+            ("outer:123",),
+        ]
+
+
+async def test_astream_without_subgraphs_skips_parent_requested_subgraph_events():
+    mock_async_client = MagicMock()
+    async_iter = MagicMock()
+    async_iter.__aiter__.return_value = _PARENT_STREAMED_PARTS
+    mock_async_client.runs.stream.return_value = async_iter
+    remote_pregel = RemoteGraph("test_graph_id", client=mock_async_client)
+
+    for stream_mode, expected in [
+        ("updates", [{"sub": {"chunk": "root"}}]),
+        # messages are not filtered: the server dedupes them across namespaces
+        ("messages", [({"content": "token"}, {})]),
+    ]:
+        parent_parts: list = []
+        stream_parts = [
+            part
+            async for part in remote_pregel.astream(
+                {"input": "data"},
+                _parent_streamed_config(parent_parts),
+                stream_mode=stream_mode,
+            )
+        ]
+
+        assert stream_parts == expected
+        # subgraph events are still requested and forwarded to the parent
+        assert mock_async_client.runs.stream.call_args.kwargs["stream_subgraphs"]
+        assert [ns for ns, _, _ in parent_parts] == [
+            ("outer:123", "sub:abc"),
+            ("outer:123", "sub:abc"),
+            ("outer:123",),
+        ]
+
+
 def test_invoke():
     # set up test
     mock_sync_client = MagicMock()

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/tests/test_run_exit.py

@@ -0,0 +1,339 @@
+"""Tests for `Runtime.on_exit`: cleanup that runs however a graph run ends."""
+
+from __future__ import annotations
+
+import asyncio
+import sys
+
+import pytest
+from langgraph.checkpoint.memory import InMemorySaver
+from typing_extensions import TypedDict
+
+from langgraph.graph import END, START, StateGraph
+from langgraph.runtime import Runtime, get_runtime
+from langgraph.types import Command, interrupt
+
+pytestmark = pytest.mark.anyio
+
+NEEDS_CONTEXTVARS = pytest.mark.skipif(
+    sys.version_info < (3, 11),
+    reason="Python 3.11+ is required for async contextvars support",
+)
+
+
+class State(TypedDict, total=False):
+    value: str
+
+
+def _two_node_graph(first, second=None, *, checkpointer=None):
+    builder = StateGraph(State)
+    builder.add_node("first", first)
+    builder.add_edge(START, "first")
+    if second is None:
+        builder.add_edge("first", END)
+    else:
+        builder.add_node("second", second)
+        builder.add_edge("first", "second")
+        builder.add_edge("second", END)
+    return builder.compile(checkpointer=checkpointer)
+
+
+# sync
+
+
+def test_runs_on_success_in_lifo_order() -> None:
+    events: list[str] = []
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup-a"))
+        runtime.on_exit(lambda: events.append("cleanup-b"))
+        events.append("first")
+        return {"value": "x"}
+
+    def second(state: State) -> State:
+        events.append("second")
+        return {}
+
+    graph = _two_node_graph(first, second)
+    assert graph.invoke({}) == {"value": "x"}
+    assert events == ["first", "second", "cleanup-b", "cleanup-a"]
+
+
+def test_runs_on_error_and_keeps_the_run_exception() -> None:
+    events: list[str] = []
+
+    def failing_cleanup() -> None:
+        events.append("failing")
+        raise KeyError("cleanup failed")
+
+    def first(state: State) -> State:
+        runtime = get_runtime()
+        runtime.on_exit(lambda: events.append("cleanup"))
+        runtime.on_exit(failing_cleanup)
+        raise ValueError("node failed")
+
+    graph = _two_node_graph(first)
+    with pytest.raises(ValueError, match="node failed"):
+        graph.invoke({})
+    # the failing callback did not stop the earlier one from running
+    assert events == ["failing", "cleanup"]
+
+
+def test_callback_error_is_raised_when_the_run_succeeded() -> None:
+    def failing_cleanup() -> None:
+        raise KeyError("cleanup failed")
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(failing_cleanup)
+        return {}
+
+    graph = _two_node_graph(first)
+    with pytest.raises(KeyError, match="cleanup failed"):
+        graph.invoke({})
+
+
+def test_runs_on_interrupt() -> None:
+    events: list[str] = []
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        return {"value": interrupt("approve?")}
+
+    graph = _two_node_graph(first, checkpointer=InMemorySaver())
+    config = {"configurable": {"thread_id": "1"}}
+    result = graph.invoke({}, config)
+    assert "__interrupt__" in result
+    assert events == ["cleanup"]
+
+    # each resumed run is its own invocation with its own callbacks
+    graph.invoke(Command(resume="ok"), config)
+    assert events == ["cleanup", "cleanup"]
+
+
+def test_runs_when_the_stream_is_closed_early() -> None:
+    events: list[str] = []
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        return {"value": "x"}
+
+    def second(state: State) -> State:
+        events.append("second")
+        return {}
+
+    graph = _two_node_graph(first, second)
+    stream = graph.stream({}, stream_mode="updates")
+    assert next(stream) == {"first": {"value": "x"}}
+    assert events == []
+    stream.close()
+    assert events == ["cleanup"]
+
+
+def test_runs_when_breaking_out_of_stream() -> None:
+    events: list[str] = []
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        return {"value": "x"}
+
+    graph = _two_node_graph(first, lambda s: {})
+    for _ in graph.stream({}, stream_mode="updates"):
+        break
+    # the dropped generator is closed by refcounting on CPython
+    assert events == ["cleanup"]
+
+
+def test_subgraph_registers_on_the_root_run() -> None:
+    events: list[str] = []
+
+    def inner(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        events.append("inner")
+        return {}
+
+    sub = StateGraph(State)
+    sub.add_node("inner", inner)
+    sub.add_edge(START, "inner")
+    subgraph = sub.compile()
+
+    def call_subgraph(state: State) -> State:
+        subgraph.invoke(state)
+        events.append("subgraph returned")
+        return {}
+
+    def after(state: State) -> State:
+        events.append("after")
+        return {}
+
+    builder = StateGraph(State)
+    builder.add_node("as_node", subgraph)
+    builder.add_node("call_subgraph", call_subgraph)
+    builder.add_node("after", after)
+    builder.add_edge(START, "as_node")
+    builder.add_edge("as_node", "call_subgraph")
+    builder.add_edge("call_subgraph", "after")
+    graph = builder.compile()
+
+    graph.invoke({})
+    # nothing runs when either subgraph ends; both run when the root ends
+    assert events == [
+        "inner",
+        "inner",
+        "subgraph returned",
+        "after",
+        "cleanup",
+        "cleanup",
+    ]
+
+
+def test_async_callback_rejected_in_sync_run() -> None:
+    async def acleanup() -> None:
+        pass
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(acleanup)
+        return {}
+
+    graph = _two_node_graph(first)
+    with pytest.raises(TypeError, match="async callback in a synchronous"):
+        graph.invoke({})
+
+
+def test_outside_a_run_raises() -> None:
+    with pytest.raises(RuntimeError, match="during a graph run"):
+        Runtime().on_exit(lambda: None)
+
+
+def test_each_invocation_gets_its_own_callbacks() -> None:
+    calls: list[int] = []
+
+    def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: calls.append(1))
+        return {}
+
+    graph = _two_node_graph(first)
+    graph.invoke({})
+    graph.invoke({})
+    assert calls == [1, 1]
+
+
+# async
+
+
+async def test_async_runs_on_success_sync_and_async_callbacks() -> None:
+    events: list[str] = []
+
+    async def acleanup() -> None:
+        await asyncio.sleep(0)
+        events.append("async-cleanup")
+
+    async def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("sync-cleanup"))
+        runtime.on_exit(acleanup)
+        events.append("first")
+        return {"value": "x"}
+
+    graph = _two_node_graph(first)
+    assert await graph.ainvoke({}) == {"value": "x"}
+    assert events == ["first", "async-cleanup", "sync-cleanup"]
+
+
+async def test_async_runs_on_error_and_keeps_the_run_exception() -> None:
+    events: list[str] = []
+
+    async def failing_cleanup() -> None:
+        raise KeyError("cleanup failed")
+
+    async def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        runtime.on_exit(failing_cleanup)
+        raise ValueError("node failed")
+
+    graph = _two_node_graph(first)
+    with pytest.raises(ValueError, match="node failed"):
+        await graph.ainvoke({})
+    assert events == ["cleanup"]
+
+
+async def test_async_runs_on_interrupt() -> None:
+    events: list[str] = []
+
+    async def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(lambda: events.append("cleanup"))
+        return {"value": interrupt("approve?")}
+
+    graph = _two_node_graph(first, checkpointer=InMemorySaver())
+    result = await graph.ainvoke({}, {"configurable": {"thread_id": "1"}})
+    assert "__interrupt__" in result
+    assert events == ["cleanup"]
+
+
+async def test_async_runs_on_cancel_after_the_node_unwinds() -> None:
+    events: list[str] = []
+    started = asyncio.Event()
+
+    async def acleanup() -> None:
+        events.append("cleanup")
+
+    async def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(acleanup)
+        started.set()
+        try:
+            await asyncio.sleep(60)
+        finally:
+            events.append("node finally")
+        return {}
+
+    graph = _two_node_graph(first)
+    task = asyncio.create_task(graph.ainvoke({}))
+    await started.wait()
+    task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await task
+    # cleanup ran after the node had stopped
+    assert events == ["node finally", "cleanup"]
+
+
+async def test_async_runs_when_the_stream_is_closed_early() -> None:
+    events: list[str] = []
+
+    async def acleanup() -> None:
+        events.append("cleanup")
+
+    async def first(state: State, runtime: Runtime) -> State:
+        runtime.on_exit(acleanup)
+        return {"value": "x"}
+
+    async def second(state: State) -> State:
+        events.append("second")
+        return {}
+
+    graph = _two_node_graph(first, second)
+    stream = graph.astream({}, stream_mode="updates")
+    assert await stream.__anext__() == {"first": {"value": "x"}}
+    assert events == []
+    await stream.aclose()
+    assert events == ["cleanup"]
+
+
+@NEEDS_CONTEXTVARS
+async def test_async_subgraph_registers_on_the_root_run() -> None:
+    events: list[str] = []
+
+    async def inner(state: State) -> State:
+        get_runtime().on_exit(lambda: events.append("cleanup"))
+        return {}
+
+    sub = StateGraph(State)
+    sub.add_node("inner", inner)
+    sub.add_edge(START, "inner")
+    subgraph = sub.compile()
+
+    async def call_subgraph(state: State) -> State:
+        await subgraph.ainvoke(state)
+        events.append("subgraph returned")
+        return {}
+
+    graph = _two_node_graph(call_subgraph, lambda s: events.append("after") or {})
+    await graph.ainvoke({})
+    assert events == ["subgraph returned", "after", "cleanup"]

libs/langgraph/tests/test_stream_namespaces.py

@@ -0,0 +1,308 @@
+import sys
+from typing import Any
+
+import pytest
+from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
+from langchain_core.messages import AIMessage
+from langchain_core.tools import tool
+
+from langgraph.func import entrypoint, task
+from langgraph.graph import START, MessagesState, StateGraph
+from langgraph.graph.message import push_message
+from langgraph.graph.state import CompiledStateGraph
+
+pytestmark = pytest.mark.anyio
+
+NEEDS_CONTEXTVARS = pytest.mark.skipif(
+    sys.version_info < (3, 11),
+    reason="Python 3.11+ is required for async contextvars support",
+)
+
+
+@tool
+def echo(text: str) -> str:
+    """Echo the text."""
+    return text
+
+
+def _one_node_graph(node: Any) -> CompiledStateGraph:
+    return (
+        StateGraph(MessagesState)
+        .add_node(node)
+        .add_edge(START, node.__name__)
+        .compile()
+    )
+
+
+def _chat_and_echo(state: MessagesState) -> dict:
+    echo.invoke({"text": "done"})
+    return {"messages": [GenericFakeChatModel(messages=iter(["one two"])).invoke("hi")]}
+
+
+async def _achat_and_echo(state: MessagesState) -> dict:
+    await echo.ainvoke({"text": "done"})
+    model = GenericFakeChatModel(messages=iter(["one two"]))
+    return {"messages": [await model.ainvoke("hi")]}
+
+
+def _segment_names(ns: tuple[str, ...]) -> tuple[str, ...]:
+    return tuple(segment.split(":")[0] for segment in ns)
+
+
+def _summary(part: dict) -> tuple[tuple[str, ...], str]:
+    if part["type"] == "messages":
+        return _segment_names(part["ns"]), part["data"][0].content
+    return _segment_names(part["ns"]), part["data"]["event"]
+
+
+_CHAT_AND_ECHO_EVENTS = [
+    ((), "tool-started"),
+    ((), "tool-finished"),
+    ((), "one"),
+    ((), " "),
+    ((), "two"),
+]
+
+_CHILD_CONFIGS = pytest.mark.parametrize(
+    "child_config",
+    [
+        None,
+        {"configurable": {"thread_id": "child"}},
+        {"configurable": {"thread_id": "parent"}},
+    ],
+    ids=["no_config", "own_thread", "caller_thread"],
+)
+
+
+_TASK_CALLERS = pytest.mark.parametrize(
+    "nested", [False, True], ids=["from_entrypoint", "from_task_in_task"]
+)
+
+
+@_TASK_CALLERS
+@pytest.mark.parametrize("subgraphs", [False, True])
+def test_task_events_stream_under_the_graph_namespace(
+    nested: bool, subgraphs: bool
+) -> None:
+    @task
+    def chat_and_echo() -> None:
+        _chat_and_echo({"messages": []})
+
+    @task
+    def outer() -> None:
+        chat_and_echo().result()
+
+    @entrypoint()
+    def workflow(inputs: dict) -> None:
+        (outer() if nested else chat_and_echo()).result()
+
+    parts = workflow.stream(
+        {}, stream_mode=["messages", "tools"], subgraphs=subgraphs, version="v2"
+    )
+
+    assert [_summary(part) for part in parts] == _CHAT_AND_ECHO_EVENTS
+
+
+@NEEDS_CONTEXTVARS
+@_TASK_CALLERS
+@pytest.mark.parametrize("subgraphs", [False, True])
+async def test_task_events_stream_under_the_graph_namespace_async(
+    nested: bool, subgraphs: bool
+) -> None:
+    @task
+    async def chat_and_echo() -> None:
+        await _achat_and_echo({"messages": []})
+
+    @task
+    async def outer() -> None:
+        await chat_and_echo()
+
+    @entrypoint()
+    async def workflow(inputs: dict) -> None:
+        await (outer() if nested else chat_and_echo())
+
+    parts = workflow.astream(
+        {}, stream_mode=["messages", "tools"], subgraphs=subgraphs, version="v2"
+    )
+
+    assert [_summary(part) async for part in parts] == _CHAT_AND_ECHO_EVENTS
+
+
+def test_task_events_stream_under_the_namespace_of_their_subgraph() -> None:
+    @task
+    def chat_and_echo() -> None:
+        _chat_and_echo({"messages": []})
+
+    def node(state: MessagesState) -> dict:
+        chat_and_echo().result()
+        return {}
+
+    sub = _one_node_graph(node)
+    parent = StateGraph(MessagesState).add_node("sub", sub).add_edge(START, "sub")
+
+    parts = parent.compile().stream(
+        {"messages": []},
+        stream_mode=["messages", "tools"],
+        subgraphs=True,
+        version="v2",
+    )
+
+    assert [_summary(part) for part in parts] == [
+        (("sub",), event) for _, event in _CHAT_AND_ECHO_EVENTS
+    ]
+
+
+@_CHILD_CONFIGS
+def test_child_graph_streams_only_to_the_node_streaming_it(
+    child_config: dict | None,
+) -> None:
+    child = _one_node_graph(_chat_and_echo)
+    received = []
+
+    def node(state: MessagesState) -> dict:
+        received.extend(
+            child.stream(
+                {"messages": []}, child_config, stream_mode=["messages", "tools"]
+            )
+        )
+        return {}
+
+    parts = _one_node_graph(node).stream(
+        {"messages": []},
+        {"configurable": {"thread_id": "parent"}},
+        stream_mode=["messages", "tools"],
+    )
+
+    assert list(parts) == []
+    assert len(received) == len(_CHAT_AND_ECHO_EVENTS)
+
+
+@NEEDS_CONTEXTVARS
+@_CHILD_CONFIGS
+async def test_child_graph_streams_only_to_the_node_streaming_it_async(
+    child_config: dict | None,
+) -> None:
+    child = _one_node_graph(_achat_and_echo)
+    received = []
+
+    async def node(state: MessagesState) -> dict:
+        stream = child.astream(
+            {"messages": []}, child_config, stream_mode=["messages", "tools"]
+        )
+        received.extend([part async for part in stream])
+        return {}
+
+    parts = _one_node_graph(node).astream(
+        {"messages": []},
+        {"configurable": {"thread_id": "parent"}},
+        stream_mode=["messages", "tools"],
+    )
+
+    assert [part async for part in parts] == []
+    assert len(received) == len(_CHAT_AND_ECHO_EVENTS)
+
+
+@pytest.mark.parametrize(
+    "child_config",
+    [
+        {"configurable": {"thread_id": "child"}},
+        {"configurable": {"thread_id": "parent"}},
+    ],
+    ids=["own_thread", "caller_thread"],
+)
+def test_child_graph_on_its_own_thread_skips_a_caller_streaming_subgraphs(
+    child_config: dict,
+) -> None:
+    child = _one_node_graph(_chat_and_echo)
+
+    def node(state: MessagesState) -> dict:
+        child.invoke({"messages": []}, child_config)
+        return {}
+
+    parts = _one_node_graph(node).stream(
+        {"messages": []},
+        {"configurable": {"thread_id": "parent"}},
+        stream_mode=["messages", "tools"],
+        subgraphs=True,
+    )
+
+    assert list(parts) == []
+
+
+def test_node_gets_the_events_of_every_subgraph_it_streams() -> None:
+    sub = _one_node_graph(_chat_and_echo)
+    counts = []
+
+    def node(state: MessagesState) -> dict:
+        for _ in range(2):
+            stream = sub.stream({"messages": []}, stream_mode=["messages", "tools"])
+            counts.append(len(list(stream)))
+        return {}
+
+    _one_node_graph(node).invoke({"messages": []})
+
+    assert counts == [len(_CHAT_AND_ECHO_EVENTS)] * 2
+
+
+@NEEDS_CONTEXTVARS
+async def test_node_gets_the_events_of_every_subgraph_it_streams_async() -> None:
+    sub = _one_node_graph(_achat_and_echo)
+    counts = []
+
+    async def node(state: MessagesState) -> dict:
+        for _ in range(2):
+            stream = sub.astream({"messages": []}, stream_mode=["messages", "tools"])
+            counts.append(len([part async for part in stream]))
+        return {}
+
+    await _one_node_graph(node).ainvoke({"messages": []})
+
+    assert counts == [len(_CHAT_AND_ECHO_EVENTS)] * 2
+
+
+def _push(state: MessagesState) -> dict:
+    push_message(AIMessage(id="pushed", content="hi"), state_key=None)
+    return {}
+
+
+def _namespaces(graph: CompiledStateGraph, subgraphs: bool) -> list[tuple[str, ...]]:
+    parts = graph.stream(
+        {"messages": []}, stream_mode="messages", subgraphs=subgraphs, version="v2"
+    )
+    return [_segment_names(part["ns"]) for part in parts]
+
+
+def _streams_pushing_graph(received: list) -> Any:
+    pushing = _one_node_graph(_push)
+
+    def node(state: MessagesState) -> dict:
+        for message, _ in pushing.stream({"messages": []}, stream_mode="messages"):
+            received.append(message.id)
+        return {}
+
+    return node
+
+
+def test_pushed_message_streams_under_the_namespace_of_its_graph() -> None:
+    pushing = _one_node_graph(_push)
+    parent = StateGraph(MessagesState).add_node("sub", pushing).add_edge(START, "sub")
+
+    assert _namespaces(pushing, subgraphs=True) == [()]
+    assert _namespaces(parent.compile(), subgraphs=False) == []
+    assert _namespaces(parent.compile(), subgraphs=True) == [("sub",)]
+
+
+def test_pushed_message_streams_to_the_node_that_streams_its_graph() -> None:
+    received: list[str] = []
+    graph = _one_node_graph(_streams_pushing_graph(received))
+
+    assert _namespaces(graph, subgraphs=False) == []
+    assert received == ["pushed"]
+
+
+def test_pushed_message_streams_to_every_stream_that_takes_it() -> None:
+    received: list[str] = []
+    graph = _one_node_graph(_streams_pushing_graph(received))
+
+    assert _namespaces(graph, subgraphs=True) == [("node",)]
+    assert received == ["pushed"]

libs/langgraph/tests/test_tool_stream_handler.py

@@ -13,13 +13,17 @@ from typing import Annotated, Any
 import pytest
 from langchain_core.messages import AIMessage
 from langchain_core.tools import tool
+from langgraph.checkpoint.memory import InMemorySaver
 from langgraph.prebuilt import ToolNode, ToolRuntime
 from typing_extensions import TypedDict
 
 from langgraph.constants import END, START
+from langgraph.errors import GraphDrained
 from langgraph.graph import StateGraph
 from langgraph.graph.message import add_messages
 from langgraph.pregel._tools import _tool_call_writer
+from langgraph.runtime import RunControl
+from langgraph.types import Command, interrupt
 
 
 class _State(TypedDict):
@@ -54,14 +58,14 @@ def _caller_async(tool_name: str, tool_args: dict[str, Any], tc_id: str = "tc1")
     return caller
 
 
-def _build_graph(caller, tools) -> Any:
+def _build_graph(caller, tools, checkpointer=None) -> Any:
     sg = StateGraph(_State)
     sg.add_node("caller", caller)
     sg.add_node("tools", ToolNode(tools))
     sg.add_edge(START, "caller")
     sg.add_edge("caller", "tools")
     sg.add_edge("tools", END)
-    return sg.compile()
+    return sg.compile(checkpointer=checkpointer)
 
 
 def _tool_events(stream) -> list[tuple[tuple[str, ...], dict]]:
@@ -146,6 +150,105 @@ class TestSyncGraphSyncTool:
         assert kinds == ["tool-started", "tool-error"]
         assert events[1][1]["message"] == "nope"
 
+    def test_interrupt_in_tool_is_not_a_tool_error(self) -> None:
+        @tool
+        def ask() -> str:
+            """asks."""
+            return interrupt("ok?")
+
+        graph = _build_graph(_caller_sync("ask", {}), [ask], InMemorySaver())
+        config = {"configurable": {"thread_id": "1"}}
+        paused = _tool_events(
+            graph.stream(
+                {"messages": []}, config, stream_mode=["tools"], subgraphs=True
+            )
+        )
+        resumed = _tool_events(
+            graph.stream(
+                Command(resume="yes"), config, stream_mode=["tools"], subgraphs=True
+            )
+        )
+
+        assert [p["event"] for _, p in paused] == ["tool-started"]
+        assert [(p["event"], p["tool_call_id"]) for _, p in resumed] == [
+            ("tool-started", "tc1"),
+            ("tool-finished", "tc1"),
+        ]
+
+    def test_tool_handing_off_to_the_parent_still_ends_its_call(self) -> None:
+        class State(TypedDict):
+            messages: Annotated[list, add_messages]
+            done: bool
+
+        def hand_off(state: State) -> Command:
+            return Command(graph=Command.PARENT, goto="finish", update={"done": True})
+
+        inner = StateGraph(State).add_node("hand_off", hand_off)
+        inner = inner.add_edge(START, "hand_off").compile()
+
+        @tool
+        def handoff() -> str:
+            """hands off."""
+            inner.invoke({"messages": [], "done": False})
+            return "unreachable"
+
+        graph = (
+            StateGraph(State)
+            .add_node("caller", _caller_sync("handoff", {}))
+            .add_node("tools", ToolNode([handoff]))
+            .add_node("finish", lambda state: {"done": True})
+            .add_edge(START, "caller")
+            .add_edge("caller", "tools")
+            .add_edge("tools", END)
+            .add_edge("finish", END)
+            .compile()
+        )
+        events = [
+            payload["event"]
+            for _, payload in _tool_events(
+                graph.stream(
+                    {"messages": [], "done": False},
+                    stream_mode=["tools"],
+                    subgraphs=True,
+                )
+            )
+        ]
+
+        assert events[0] == "tool-started"
+        assert events[-1] == "tool-error", events
+
+    def test_drained_tool_is_not_a_tool_error(self) -> None:
+        control = RunControl()
+
+        def request_drain(state: _State) -> dict:
+            control.request_drain()
+            return {}
+
+        inner = (
+            StateGraph(_State)
+            .add_node("request_drain", request_drain)
+            .add_node("after", lambda state: {})
+            .add_edge(START, "request_drain")
+            .add_edge("request_drain", "after")
+            .compile()
+        )
+
+        @tool
+        def drained() -> str:
+            """drains."""
+            inner.invoke({"messages": []}, control=control)
+            return "unreachable"
+
+        graph = _build_graph(_caller_sync("drained", {}), [drained])
+        chunks: list = []
+        with pytest.raises(GraphDrained):
+            for chunk in graph.stream(
+                {"messages": []}, stream_mode=["tools"], subgraphs=True
+            ):
+                chunks.append(chunk)
+
+        assert [p["event"] for _, p in _tool_events(chunks)] == ["tool-started"]
+
     def test_writer_unset_outside_tool(self) -> None:
         # Outside any tool body the ContextVar that ToolRuntime reads
         # is unset — emitting from there would be a no-op.
@@ -196,6 +299,25 @@ class TestAsyncGraphAsyncTool:
         assert kinds == ["tool-started", "tool-output-delta", "tool-finished"]
         assert events[1][1]["delta"] == "hi"
 
+    @pytest.mark.anyio
+    async def test_interrupt_in_async_tool_is_not_a_tool_error(self) -> None:
+        @tool
+        async def aask() -> str:
+            """asks."""
+            return interrupt("ok?")
+
+        graph = _build_graph(_caller_async("aask", {}), [aask], InMemorySaver())
+        config = {"configurable": {"thread_id": "1"}}
+        events = []
+        for graph_input in ({"messages": []}, Command(resume="yes")):
+            async for ns, mode, payload in graph.astream(
+                graph_input, config, stream_mode=["tools"], subgraphs=True
+            ):
+                if mode == "tools":
+                    events.append(payload["event"])
+
+        assert events == ["tool-started", "tool-started", "tool-finished"]
+
 
 class TestConcurrentToolCalls:
     def test_parallel_tool_calls_do_not_bleed(self) -> None:

libs/langgraph/tests/test_trace_policy.py

@@ -1,11 +1,24 @@
 """End-to-end tests for `TracePolicy` input processing on node trace runs."""
 
+import asyncio
+from collections.abc import AsyncIterator, Iterator
 from typing import Any
+from uuid import UUID
 
 import pytest
+from langchain_core.callbacks import BaseCallbackHandler
+from langchain_core.language_models.fake_chat_models import FakeMessagesListChatModel
+from langchain_core.messages import AIMessage, HumanMessage
+from langchain_core.runnables import RunnableConfig
 from typing_extensions import TypedDict
 
-from langgraph.graph import END, START, StateGraph
+from langgraph._internal._runnable import (
+    ASYNCIO_ACCEPTS_CONTEXT,
+    RunnableCallable,
+    RunnableSeq,
+)
+from langgraph.graph import END, START, MessagesState, StateGraph
+from langgraph.graph.state import CompiledStateGraph
 from langgraph.types import TracePolicy
 from tests.fake_tracer import FakeTracer, Run
 
@@ -147,3 +160,179 @@ async def test_trace_policy_transforms_recorded_inputs_async() -> None:
     run = _node_run(tracer, "n")
     assert run.inputs == {"scrubbed_in": True}
     assert run.outputs == {"value": 6}
+
+
+_RECORDING_POLICY = TracePolicy(
+    process_inputs=lambda _: {"recorded": "inputs"},
+    process_outputs=lambda _: {"recorded": "outputs"},
+)
+
+
+def _chat_graph() -> CompiledStateGraph:
+    model = FakeMessagesListChatModel(
+        responses=[AIMessage("model reply", id="ai-model")]
+    )
+
+    def chat(state: MessagesState) -> dict[str, Any]:
+        reply = model.invoke(state["messages"])
+        return {
+            "messages": [
+                *state["messages"],
+                reply,
+                AIMessage("from node", id="ai-node"),
+            ]
+        }
+
+    return (
+        StateGraph(MessagesState)
+        .add_node("chat", chat, trace_policy=_RECORDING_POLICY)
+        .add_edge(START, "chat")
+        .compile()
+    )
+
+
+def _assert_scrubbed_node_run(tracer: FakeTracer, *, model_is_child: bool) -> None:
+    run = _node_run(tracer, "chat")
+    assert run.inputs == {"recorded": "inputs"}
+    assert run.outputs == {"recorded": "outputs"}
+    if model_is_child:
+        assert [c.name for c in run.child_runs] == ["FakeMessagesListChatModel"]
+
+
+def test_trace_policy_scrubs_tracer_not_messages_stream() -> None:
+    tracer = FakeTracer()
+    streamed = [
+        message.content
+        for message, _ in _chat_graph().stream(
+            {"messages": [HumanMessage("hello", id="h-1")]},
+            {"callbacks": [tracer]},
+            stream_mode="messages",
+        )
+    ]
+
+    assert streamed == ["model reply", "from node"]
+    _assert_scrubbed_node_run(tracer, model_is_child=True)
+
+
+@pytest.mark.anyio
+async def test_trace_policy_scrubs_tracer_not_messages_stream_async() -> None:
+    tracer = FakeTracer()
+    streamed = [
+        message.content
+        async for message, _ in _chat_graph().astream(
+            {"messages": [HumanMessage("hello", id="h-1")]},
+            {"callbacks": [tracer]},
+            stream_mode="messages",
+        )
+    ]
+
+    assert streamed == ["model reply", "from node"]
+    _assert_scrubbed_node_run(tracer, model_is_child=ASYNCIO_ACCEPTS_CONTEXT)
+
+
+@pytest.mark.anyio
+async def test_trace_policy_scrubs_tracer_not_astream_events() -> None:
+    tracer = FakeTracer()
+    chat_events = [
+        event
+        async for event in _chat_graph().astream_events(
+            {"messages": [HumanMessage("hello", id="h-1")]},
+            {"callbacks": [tracer]},
+            version="v2",
+        )
+        if event["name"] == "chat"
+        and event["event"] in ("on_chain_start", "on_chain_end")
+    ]
+
+    assert [e["event"] for e in chat_events] == ["on_chain_start", "on_chain_end"]
+    start, end = (e["data"] for e in chat_events)
+    assert [m.content for m in start["input"]["messages"]] == ["hello"]
+    assert [m.content for m in end["output"]["messages"]] == [
+        "hello",
+        "model reply",
+        "from node",
+    ]
+    _assert_scrubbed_node_run(tracer, model_is_child=ASYNCIO_ACCEPTS_CONTEXT)
+
+
+class _HandlerWithTapMethods(BaseCallbackHandler):
+    def __init__(self) -> None:
+        self.node_payloads: list[Any] = []
+        self.node_run_ids: set[UUID] = set()
+
+    def _record(self, run_id: UUID, payload: Any) -> None:
+        if run_id in self.node_run_ids:
+            self.node_payloads.append(payload)
+
+    def tap_output_iter(self, run_id: UUID, output: Iterator[Any]) -> Iterator[Any]:
+        for chunk in output:
+            self._record(run_id, chunk)
+            yield chunk
+
+    async def tap_output_aiter(
+        self, run_id: UUID, output: AsyncIterator[Any]
+    ) -> AsyncIterator[Any]:
+        async for chunk in output:
+            self._record(run_id, chunk)
+            yield chunk
+
+    def on_chain_start(
+        self, serialized: Any, inputs: Any, *, run_id: UUID, **kwargs: Any
+    ) -> None:
+        if kwargs.get("name") == "n":
+            self.node_run_ids.add(run_id)
+            self._record(run_id, inputs)
+
+    def on_chain_end(self, outputs: Any, *, run_id: UUID, **kwargs: Any) -> None:
+        self._record(run_id, outputs)
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize("via_events", [False, True], ids=["ainvoke", "astream_events"])
+async def test_trace_policy_reaches_tracers_but_not_custom_handlers(
+    via_events: bool,
+) -> None:
+    graph = (
+        StateGraph(State)
+        .add_node("n", _incr, trace_policy=_RECORDING_POLICY)
+        .add_edge(START, "n")
+        .add_edge("n", END)
+        .compile()
+    )
+    handler = _HandlerWithTapMethods()
+    tracer = FakeTracer()
+    config: RunnableConfig = {"callbacks": [handler, tracer]}
+
+    if via_events:
+        async for _ in graph.astream_events({"value": 1}, config, version="v2"):
+            pass
+    else:
+        assert await graph.ainvoke({"value": 1}, config) == {"value": 2}
+    assert handler.node_payloads == [{"value": 1}, {"value": 2}]
+    run = _node_run(tracer, "n")
+    assert (run.inputs, run.outputs) == (
+        {"recorded": "inputs"},
+        {"recorded": "outputs"},
+    )
+
+
+@pytest.mark.anyio
+async def test_trace_policy_cancel_at_node_end_still_closes_tracer_run() -> None:
+    def cancel_own_task(value: Any) -> Any:
+        asyncio.current_task().cancel()
+        return value
+
+    tracer = FakeTracer()
+    seq = RunnableSeq(
+        RunnableCallable(lambda x: x, trace=False),
+        RunnableCallable(cancel_own_task, trace=False),
+        trace_policy=_RECORDING_POLICY,
+    )
+    with pytest.raises(asyncio.CancelledError):
+        await asyncio.create_task(seq.ainvoke({}, {"callbacks": [tracer]}))
+    for _ in range(100):
+        if tracer.runs:
+            break
+        await asyncio.sleep(0.01)
+
+    assert [r.outputs for r in tracer.runs] == [{"recorded": "outputs"}]

libs/langgraph/uv.lock

@@ -1439,7 +1439,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.19"
 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" },
@@ -1722,7 +1722,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint-sqlite"
-version = "3.1.2"
+version = "3.1.3"
 source = { editable = "../checkpoint-sqlite" }
 dependencies = [
     { name = "aiosqlite" },
@@ -3419,11 +3419,11 @@ wheels = [
 
 [[package]]
 name = "setuptools"
-version = "83.0.0"
+version = "84.1.0"
 source = { registry = "https://pypi.org/simple" }
-sdist = { url = "https://files.pythonhosted.org/packages/34/26/f5d29e25ffdb535afef2d35cdb55b325298f96debd670da4c325e08d70f4/setuptools-83.0.0.tar.gz", hash = "sha256:025bccbbf0fa05b6192bc64ae1e7b16e001fd6d6d4d5de03c97b1c1ade523bef", size = 1154254, upload-time = "2026-07-04T15:31:22.699Z" }
+sdist = { url = "https://files.pythonhosted.org/packages/73/eb/7e5f628ee2eb168fecbf8026de7856b2543d6d609cc85f086b9a91ac93d6/setuptools-84.1.0.tar.gz", hash = "sha256:23657205b63d4d31395ab917815247f694aafad28cd21316bf5fd45a51048ea0", size = 1171783, upload-time = "2026-10-19T20:11:43.489Z" }
 wheels = [
-    { url = "https://files.pythonhosted.org/packages/5d/40/e1e72872c6354b306daef1703549e8e83b4d43cfea356311bf722a043752/setuptools-83.0.0-py3-none-any.whl", hash = "sha256:29b23c360f22f414dc7336bb39178cc7bcbf6021ed2733cde173f09dba19abb3", size = 1008090, upload-time = "2026-07-04T15:31:20.885Z" },
+    { url = "https://files.pythonhosted.org/packages/18/02/b4bbb90f8f29e334898ff45c6d9b1fffaa6f378017052b3023a06262b5f7/setuptools-84.1.0-py3-none-any.whl", hash = "sha256:5231689c6ac8156cd155cfb98c3fd6fb252c3e7e9bd3d78b64d3c55f132624c9", size = 819380, upload-time = "2026-10-19T20:11:41.684Z" },
 ]
 
 [[package]]

libs/prebuilt/uv.lock

@@ -286,7 +286,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.19"
 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" },
@@ -467,7 +467,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint-sqlite"
-version = "3.1.2"
+version = "3.1.3"
 source = { editable = "../checkpoint-sqlite" }
 dependencies = [
     { name = "aiosqlite" },

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__ = "0.4.11"
 
 __all__ = [
     "Auth",

libs/sdk-py/langgraph_sdk/_async/http.py

@@ -14,9 +14,14 @@ import orjson
 
 from langgraph_sdk._shared.utilities import (
     _orjson_default,
+    _reconnect_delay,
     _validate_reconnect_location,
 )
-from langgraph_sdk.errors import _araise_for_status_typed
+from langgraph_sdk.errors import (
+    InternalServerError,
+    RateLimitError,
+    _araise_for_status_typed,
+)
 from langgraph_sdk.schema import QueryParamTypes, StreamPart
 from langgraph_sdk.sse import SSEDecoder, aiter_lines_raw
 
@@ -146,7 +151,8 @@ class HttpClient:
         on_response: Callable[[httpx.Response], None] | None = None,
         reconnect_limit: int = 5,
     ) -> Any:
-        """Send a request that automatically reconnects to Location header."""
+        """Send a request that reconnects to its Location header if the response is
+        cut off, with backoff between attempts."""
         request_headers, content = await _aencode_json(json)
         if headers:
             request_headers.update(headers)
@@ -176,13 +182,27 @@ class HttpClient:
                     stacklevel=2,
                 )
                 await r.aclose()
-                return await self.request_reconnect(
-                    loc,
-                    "GET",
-                    headers=headers,
-                    # don't pass on_response so it's only called once
-                    reconnect_limit=reconnect_limit - 1,
-                )
+                for attempt in range(reconnect_limit):
+                    await asyncio.sleep(_reconnect_delay(attempt, base=1.0, cap=5.0))
+                    # A restart or a deploy looks like a refused connection, a
+                    # dropped body, a 429 or a 5xx; other errors won't go away.
+                    try:
+                        return await self.request_reconnect(
+                            loc,
+                            "GET",
+                            headers=headers,
+                            # don't pass on_response so it's only called once
+                            reconnect_limit=0,
+                        )
+                    except httpx.HTTPStatusError as err:
+                        status = err.response.status_code
+                        if attempt == reconnect_limit - 1 or (
+                            status != 429 and status < 500
+                        ):
+                            raise
+                    except httpx.TransportError:
+                        if attempt == reconnect_limit - 1:
+                            raise
 
     async def stream(
         self,
@@ -217,72 +237,104 @@ class HttpClient:
             current_headers = dict(
                 request_headers if reconnect_path is None else reconnect_headers
             )
+            if last_event_id is not None:
+                current_headers = {
+                    key: value
+                    for key, value in current_headers.items()
+                    if key.lower() != "last-event-id"
+                }
             if last_event_id:
                 current_headers["Last-Event-ID"] = last_event_id
+            if reconnect_path is not None and not any(
+                key.lower() == "last-event-id" and value
+                for key, value in current_headers.items()
+            ):
+                warnings.warn(
+                    "Reconnecting without a Last-Event-ID, so events sent while "
+                    "disconnected are not replayed. Only runs created with "
+                    "stream_resumable=True send the event IDs a reconnect resumes "
+                    "from.",
+                    stacklevel=2,
+                )
 
             current_method = method if reconnect_path is None else "GET"
             current_content = content if reconnect_path is None else None
             current_params = params if reconnect_path is None else None
 
-            retry = False
-            async with self.client.stream(
-                current_method,
-                reconnect_path or path,
-                headers=current_headers,
-                content=current_content,
-                params=current_params,
-            ) as res:
-                if reconnect_path is None and on_response:
-                    on_response(res)
-                # check status
-                await _araise_for_status_typed(res)
-                # check content type
-                content_type = res.headers.get("content-type", "").partition(";")[0]
-                if "text/event-stream" not in content_type:
-                    raise httpx.TransportError(
-                        "Expected response header Content-Type to contain 'text/event-stream', "
-                        f"got {content_type!r}"
-                    )
+            reconnect_cause: httpx.HTTPError | None = None
+            try:
+                async with self.client.stream(
+                    current_method,
+                    reconnect_path or path,
+                    headers=current_headers,
+                    content=current_content,
+                    params=current_params,
+                ) as res:
+                    if reconnect_path is None and on_response:
+                        on_response(res)
+                    # check status
+                    await _araise_for_status_typed(res)
+                    # check content type
+                    content_type = res.headers.get("content-type", "").partition(";")[0]
+                    if "text/event-stream" not in content_type:
+                        raise httpx.TransportError(
+                            "Expected response header Content-Type to contain 'text/event-stream', "
+                            f"got {content_type!r}"
+                        )
 
-                reconnect_location = res.headers.get("location")
-                if reconnect_location:
-                    _validate_reconnect_location(
-                        self.client.base_url, reconnect_location
-                    )
-                    reconnect_path = reconnect_location
+                    reconnect_location = res.headers.get("location")
+                    if reconnect_location:
+                        _validate_reconnect_location(
+                            self.client.base_url, reconnect_location
+                        )
+                        reconnect_path = reconnect_location
 
-                # parse SSE
-                decoder = SSEDecoder()
-                try:
-                    async for line in aiter_lines_raw(res):
-                        sse = decoder.decode(line=cast("bytes", line).rstrip(b"\n"))
-                        if sse is not None:
+                    # parse SSE
+                    decoder = SSEDecoder(last_event_id=last_event_id)
+                    try:
+                        async for line in aiter_lines_raw(res):
+                            sse = decoder.decode(line=cast("bytes", line).rstrip(b"\n"))
+                            if sse is not None:
+                                if decoder.last_event_id is not None:
+                                    last_event_id = decoder.last_event_id
+                                if sse.event or decoder.has_data:
+                                    # Progress since the last drop earns a fresh
+                                    # set of reconnect attempts.
+                                    reconnect_attempts = 0
+                                    yield sse
+                    except httpx.HTTPError as err:
+                        # httpx.TransportError inherits from HTTPError, so transient
+                        # disconnects during streaming land here.
+                        if reconnect_path is None:
+                            raise
+                        reconnect_cause = err
+                    else:
+                        if sse := decoder.decode(b""):
                             if decoder.last_event_id is not None:
                                 last_event_id = decoder.last_event_id
-                            if sse.event or sse.data is not None:
+                            if sse.event or decoder.has_data:
+                                # decoder.decode(b"") flushes the in-flight event and may
+                                # return an empty placeholder when there is no pending
+                                # message. Skip these no-op events so the stream doesn't
+                                # emit a trailing blank item after reconnects.
                                 yield sse
-                except httpx.HTTPError:
-                    # httpx.TransportError inherits from HTTPError, so transient
-                    # disconnects during streaming land here.
-                    if reconnect_path is None:
-                        raise
-                    retry = True
-                else:
-                    if sse := decoder.decode(b""):
-                        if decoder.last_event_id is not None:
-                            last_event_id = decoder.last_event_id
-                        if sse.event or sse.data is not None:
-                            # decoder.decode(b"") flushes the in-flight event and may
-                            # return an empty placeholder when there is no pending
-                            # message. Skip these no-op events so the stream doesn't
-                            # emit a trailing blank item after reconnects.
-                            yield sse
-            if retry:
+            except (httpx.TransportError, RateLimitError, InternalServerError) as err:
+                # A reconnect that can't open (connection refused, 429, 5xx or a
+                # non-SSE body) usually means the server is restarting or
+                # mid-deploy, so retry it like a drop. Before the server sends a
+                # Location there is nothing to reconnect to, so raise.
+                if reconnect_path is None:
+                    raise
+                reconnect_cause = err
+            if reconnect_cause is not None:
                 reconnect_attempts += 1
                 if reconnect_attempts > max_reconnect_attempts:
                     raise httpx.TransportError(
                         "Exceeded maximum SSE reconnection attempts"
-                    )
+                    ) from reconnect_cause
+                await asyncio.sleep(
+                    _reconnect_delay(reconnect_attempts - 1, base=1.0, cap=5.0)
+                )
                 continue
             break
 

libs/sdk-py/langgraph_sdk/_async/stream.py

@@ -16,7 +16,6 @@ from __future__ import annotations
 import asyncio
 import contextlib
 import logging
-import random
 from collections.abc import AsyncGenerator, AsyncIterator, Generator, Mapping
 from dataclasses import dataclass, field
 from typing import Any, Literal, TypedDict, cast
@@ -25,7 +24,7 @@ from langchain_core.language_models.chat_model_stream import AsyncChatModelStrea
 from langchain_protocol import Event, SubscribeParams
 
 from langgraph_sdk._async.http import HttpClient
-from langgraph_sdk._shared.utilities import _quote_path_param
+from langgraph_sdk._shared.utilities import _quote_path_param, _reconnect_delay
 from langgraph_sdk.schema import LangSmithTracing, QueryParamTypes
 from langgraph_sdk.stream.controller import _SeenEventIds
 from langgraph_sdk.stream.decoders import (
@@ -1691,11 +1690,13 @@ class AsyncThreadStream:
 
     async def _reconnect_sleep(self, attempt: int) -> None:
         """Sleep with exponential backoff and jitter for reconnect attempt `attempt`."""
-        base = self._shared_reconnect_backoff_base
-        cap = self._shared_reconnect_backoff_cap
-        delay = min(cap, base * (2**attempt))
-        jitter = random.uniform(0, delay * 0.25)
-        await asyncio.sleep(delay + jitter)
+        await asyncio.sleep(
+            _reconnect_delay(
+                attempt,
+                base=self._shared_reconnect_backoff_base,
+                cap=self._shared_reconnect_backoff_cap,
+            )
+        )
 
     async def _reconnect_shared_stream(self) -> bool:
         """Attempt to reopen the shared stream after a post-ready transport drop.

libs/sdk-py/langgraph_sdk/_shared/utilities.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import functools
 import os
+import random
 import re
 from collections.abc import Mapping
 from datetime import tzinfo
@@ -194,6 +195,15 @@ def _validate_reconnect_location(base_url: httpx.URL, location: str) -> str:
     return location
 
 
+def _reconnect_delay(attempt: int, *, base: float, cap: float) -> float:
+    """Seconds to wait before reconnect attempt `attempt` (0-based).
+
+    Exponential backoff capped at `cap`, plus up to 25% jitter.
+    """
+    delay = min(cap, base * (2**attempt))
+    return delay + random.uniform(0, delay * 0.25)
+
+
 def _provided_vals(d: Mapping[str, Any]) -> dict[str, Any]:
     return {k: v for k, v in d.items() if v is not None}
 

libs/sdk-py/langgraph_sdk/_sync/http.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import logging
 import sys
+import time
 import warnings
 from collections.abc import Callable, Iterator, Mapping
 from typing import Any, cast
@@ -13,9 +14,14 @@ import orjson
 
 from langgraph_sdk._shared.utilities import (
     _orjson_default,
+    _reconnect_delay,
     _validate_reconnect_location,
 )
-from langgraph_sdk.errors import _raise_for_status_typed
+from langgraph_sdk.errors import (
+    InternalServerError,
+    RateLimitError,
+    _raise_for_status_typed,
+)
 from langgraph_sdk.schema import QueryParamTypes, StreamPart
 from langgraph_sdk.sse import SSEDecoder, iter_lines_raw
 
@@ -146,7 +152,8 @@ class SyncHttpClient:
         on_response: Callable[[httpx.Response], None] | None = None,
         reconnect_limit: int = 5,
     ) -> Any:
-        """Send a request that automatically reconnects to Location header."""
+        """Send a request that reconnects to its Location header if the response is
+        cut off, with backoff between attempts."""
         request_headers, content = _encode_json(json)
         if headers:
             request_headers.update(headers)
@@ -176,13 +183,27 @@ class SyncHttpClient:
                     stacklevel=2,
                 )
                 r.close()
-                return self.request_reconnect(
-                    loc,
-                    "GET",
-                    headers=headers,
-                    # don't pass on_response so it's only called once
-                    reconnect_limit=reconnect_limit - 1,
-                )
+                for attempt in range(reconnect_limit):
+                    time.sleep(_reconnect_delay(attempt, base=1.0, cap=5.0))
+                    # A restart or a deploy looks like a refused connection, a
+                    # dropped body, a 429 or a 5xx; other errors won't go away.
+                    try:
+                        return self.request_reconnect(
+                            loc,
+                            "GET",
+                            headers=headers,
+                            # don't pass on_response so it's only called once
+                            reconnect_limit=0,
+                        )
+                    except httpx.HTTPStatusError as err:
+                        status = err.response.status_code
+                        if attempt == reconnect_limit - 1 or (
+                            status != 429 and status < 500
+                        ):
+                            raise
+                    except httpx.TransportError:
+                        if attempt == reconnect_limit - 1:
+                            raise
 
     def stream(
         self,
@@ -219,69 +240,99 @@ class SyncHttpClient:
             current_headers = dict(
                 request_headers if reconnect_path is None else reconnect_headers
             )
+            if last_event_id is not None:
+                current_headers = {
+                    key: value
+                    for key, value in current_headers.items()
+                    if key.lower() != "last-event-id"
+                }
             if last_event_id:
                 current_headers["Last-Event-ID"] = last_event_id
+            if reconnect_path is not None and not any(
+                key.lower() == "last-event-id" and value
+                for key, value in current_headers.items()
+            ):
+                warnings.warn(
+                    "Reconnecting without a Last-Event-ID, so events sent while "
+                    "disconnected are not replayed. Only runs created with "
+                    "stream_resumable=True send the event IDs a reconnect resumes "
+                    "from.",
+                    stacklevel=2,
+                )
 
             current_method = method if reconnect_path is None else "GET"
             current_content = content if reconnect_path is None else None
             current_params = params if reconnect_path is None else None
 
-            retry = False
-            with self.client.stream(
-                current_method,
-                reconnect_path or path,
-                headers=current_headers,
-                content=current_content,
-                params=current_params,
-            ) as res:
-                if reconnect_path is None and on_response:
-                    on_response(res)
-                # check status
-                _raise_for_status_typed(res)
-                # check content type
-                content_type = res.headers.get("content-type", "").partition(";")[0]
-                if "text/event-stream" not in content_type:
-                    raise httpx.TransportError(
-                        "Expected response header Content-Type to contain 'text/event-stream', "
-                        f"got {content_type!r}"
-                    )
+            reconnect_cause: httpx.HTTPError | None = None
+            try:
+                with self.client.stream(
+                    current_method,
+                    reconnect_path or path,
+                    headers=current_headers,
+                    content=current_content,
+                    params=current_params,
+                ) as res:
+                    if reconnect_path is None and on_response:
+                        on_response(res)
+                    # check status
+                    _raise_for_status_typed(res)
+                    # check content type
+                    content_type = res.headers.get("content-type", "").partition(";")[0]
+                    if "text/event-stream" not in content_type:
+                        raise httpx.TransportError(
+                            "Expected response header Content-Type to contain 'text/event-stream', "
+                            f"got {content_type!r}"
+                        )
 
-                reconnect_location = res.headers.get("location")
-                if reconnect_location:
-                    _validate_reconnect_location(
-                        self.client.base_url, reconnect_location
-                    )
-                    reconnect_path = reconnect_location
+                    reconnect_location = res.headers.get("location")
+                    if reconnect_location:
+                        _validate_reconnect_location(
+                            self.client.base_url, reconnect_location
+                        )
+                        reconnect_path = reconnect_location
 
-                decoder = SSEDecoder()
-                try:
-                    for line in iter_lines_raw(res):
-                        sse = decoder.decode(cast(bytes, line).rstrip(b"\n"))
-                        if sse is not None:
+                    decoder = SSEDecoder(last_event_id=last_event_id)
+                    try:
+                        for line in iter_lines_raw(res):
+                            sse = decoder.decode(cast(bytes, line).rstrip(b"\n"))
+                            if sse is not None:
+                                if decoder.last_event_id is not None:
+                                    last_event_id = decoder.last_event_id
+                                if sse.event or decoder.has_data:
+                                    # Progress since the last drop earns a fresh
+                                    # set of reconnect attempts.
+                                    reconnect_attempts = 0
+                                    yield sse
+                    except httpx.HTTPError as err:
+                        # httpx.TransportError inherits from HTTPError, so transient
+                        # disconnects during streaming land here.
+                        if reconnect_path is None:
+                            raise
+                        reconnect_cause = err
+                    else:
+                        if sse := decoder.decode(b""):
                             if decoder.last_event_id is not None:
                                 last_event_id = decoder.last_event_id
-                            if sse.event or sse.data is not None:
+                            if sse.event or decoder.has_data:
+                                # See async stream implementation for rationale on
+                                # skipping empty flush events.
                                 yield sse
-                except httpx.HTTPError:
-                    # httpx.TransportError inherits from HTTPError, so transient
-                    # disconnects during streaming land here.
-                    if reconnect_path is None:
-                        raise
-                    retry = True
-                else:
-                    if sse := decoder.decode(b""):
-                        if decoder.last_event_id is not None:
-                            last_event_id = decoder.last_event_id
-                        if sse.event or sse.data is not None:
-                            # See async stream implementation for rationale on
-                            # skipping empty flush events.
-                            yield sse
-            if retry:
+            except (httpx.TransportError, RateLimitError, InternalServerError) as err:
+                # A reconnect that can't open (connection refused, 429, 5xx or a
+                # non-SSE body) usually means the server is restarting or
+                # mid-deploy, so retry it like a drop. Before the server sends a
+                # Location there is nothing to reconnect to, so raise.
+                if reconnect_path is None:
+                    raise
+                reconnect_cause = err
+            if reconnect_cause is not None:
                 reconnect_attempts += 1
                 if reconnect_attempts > max_reconnect_attempts:
                     raise httpx.TransportError(
                         "Exceeded maximum SSE reconnection attempts"
-                    )
+                    ) from reconnect_cause
+                time.sleep(_reconnect_delay(reconnect_attempts - 1, base=1.0, cap=5.0))
                 continue
             break
 

libs/sdk-py/langgraph_sdk/auth/__init__.py

@@ -811,7 +811,7 @@ class _On:
     def __call__(
         self,
         *,
-        resources: str | Sequence[str],
+        resources: str | Sequence[str] | None = None,
         actions: str | Sequence[str] | None = None,
     ) -> Callable[[AHO], AHO]: ...
 

libs/sdk-py/langgraph_sdk/sse.py

@@ -30,18 +30,14 @@ class BytesLineDecoder:
         # See https://docs.python.org/3/glossary.html#term-universal-newlines
         NEWLINE_CHARS = b"\n\r"
 
-        # We always push a trailing `\r` into the next decode iteration.
-        if self.trailing_cr:
-            text = b"\r" + text
-            self.trailing_cr = False
-        if text.endswith(b"\r"):
-            self.trailing_cr = True
-            text = text[:-1]
+        if not text:
+            return []
+        if self.trailing_cr and text.startswith(b"\n"):
+            text = text[1:]
+        self.trailing_cr = text.endswith(b"\r")
 
         if not text:
-            # NOTE: the edge case input of empty text doesn't occur in practice,
-            # because other httpx internals filter out this value
-            return []  # pragma: no cover
+            return []
 
         trailing_newline = text[-1] in NEWLINE_CHARS
         lines = cast(list[BytesLike], text.splitlines())
@@ -66,7 +62,7 @@ class BytesLineDecoder:
         return lines
 
     def flush(self) -> list[BytesLike]:
-        if not self.buffer and not self.trailing_cr:
+        if not self.buffer:
             return []
 
         lines: list[BytesLike] = [self.buffer]
@@ -76,18 +72,25 @@ class BytesLineDecoder:
 
 
 class SSEDecoder:
-    def __init__(self) -> None:
+    def __init__(self, *, last_event_id: str | None = None) -> None:
         self._event = ""
         self._data = bytearray()
-        self._last_event_id: str | None = None
+        self._last_event_id = last_event_id
         self._retry: int | None = None
         self._at_stream_start = True
+        self._has_data = False
+        self._id_changed = False
+
+    @property
+    def has_data(self) -> bool:
+        """Whether the last decoded block contained a data field."""
+        return self._has_data
 
     @property
     def last_event_id(self) -> str | None:
         """Return the last event identifier that was seen.
 
-        `None` until the stream sends an `id` field, and `""` after an empty
+        `None` until an ID is supplied or received, and `""` after an empty
         one, which resets the reconnect cursor.
         """
 
@@ -101,17 +104,26 @@ class SSEDecoder:
             line = line.removeprefix(b"\xef\xbb\xbf")
 
         if not line:
+            self._has_data = bool(self._data)
             if (
                 not self._event
                 and not self._data
-                and not self._last_event_id
+                and not self._id_changed
                 and self._retry is None
             ):
                 return None
 
+            body = self._data[:-1]
+            data = None
+            if body and not body.isspace():
+                try:
+                    data = orjson.loads(body)
+                except orjson.JSONDecodeError:
+                    data = orjson.loads(body.decode(errors="replace"))
+
             sse = StreamPart(
                 event=self._event,
-                data=orjson.loads(self._data) if self._data else None,  # ty: ignore[invalid-argument-type]
+                data=data,  # ty: ignore[invalid-argument-type]
                 id=self._last_event_id or None,
             )
 
@@ -119,6 +131,7 @@ class SSEDecoder:
             self._event = ""
             self._data = bytearray()
             self._retry = None
+            self._id_changed = False
 
             return sse
 
@@ -131,16 +144,16 @@ class SSEDecoder:
             value = value[1:]
 
         if fieldname == b"event":
-            self._event = value.decode()
+            self._event = value.decode(errors="replace")
         elif fieldname == b"data":
-            if self._data:
-                self._data.extend(b"\n")
             self._data.extend(value)
+            self._data.extend(b"\n")
         elif fieldname == b"id":
             if b"\0" in value:
                 pass
             else:
-                self._last_event_id = value.decode()
+                self._last_event_id = value.decode(errors="replace")
+                self._id_changed = True
         elif fieldname == b"retry":
             with contextlib.suppress(TypeError, ValueError):
                 self._retry = int(value)

libs/sdk-py/langgraph_sdk/stream/controller.py

@@ -15,7 +15,6 @@ from __future__ import annotations
 import asyncio
 import contextlib
 import logging
-import random
 from collections import OrderedDict
 from collections.abc import AsyncGenerator, AsyncIterator, Awaitable, Callable
 from dataclasses import dataclass, field
@@ -23,6 +22,7 @@ from typing import Any
 
 from langchain_protocol import Event, SubscribeParams
 
+from langgraph_sdk._shared.utilities import _reconnect_delay
 from langgraph_sdk.stream.transport import AsyncProtocolTransport, EventStreamHandle
 
 # ---------------------------------------------------------------------------
@@ -275,11 +275,13 @@ class StreamController:
 
     async def _reconnect_sleep(self, attempt: int) -> None:
         """Sleep with exponential backoff and jitter for reconnect attempt *attempt*."""
-        base = self._reconnect_backoff_base
-        cap = self._reconnect_backoff_cap
-        delay = min(cap, base * (2**attempt))
-        jitter = random.uniform(0, delay * 0.25)
-        await asyncio.sleep(delay + jitter)
+        await asyncio.sleep(
+            _reconnect_delay(
+                attempt,
+                base=self._reconnect_backoff_base,
+                cap=self._reconnect_backoff_cap,
+            )
+        )
 
     async def _reconnect_shared_stream(self) -> bool:
         """Attempt to reopen the shared stream after a transport drop.

libs/sdk-py/langgraph_sdk/stream/sync_controller.py

@@ -4,7 +4,6 @@ from __future__ import annotations
 
 import contextlib
 import logging
-import random
 import threading
 import time
 from dataclasses import dataclass, field
@@ -13,6 +12,7 @@ from typing import Any
 
 from langchain_protocol import Event, SubscribeParams
 
+from langgraph_sdk._shared.utilities import _reconnect_delay
 from langgraph_sdk.stream.errors import (
     is_non_retryable_stream_error,
     stream_error_frame,
@@ -282,11 +282,13 @@ class SyncStreamController:
 
     def _reconnect_sleep(self, attempt: int) -> None:
         """Sleep with exponential backoff + jitter before a reconnect attempt."""
-        base = self._reconnect_backoff_base
-        cap = self._reconnect_backoff_cap
-        delay = min(cap, base * (2**attempt))
-        jitter = random.uniform(0, delay * 0.25)
-        time.sleep(delay + jitter)
+        time.sleep(
+            _reconnect_delay(
+                attempt,
+                base=self._reconnect_backoff_base,
+                cap=self._reconnect_backoff_cap,
+            )
+        )
 
     def _reconnect_shared_stream(self) -> bool:
         """Attempt to reopen the shared stream after a transport drop.

libs/sdk-py/tests/conftest.py

@@ -0,0 +1,17 @@
+import asyncio
+import time
+
+import pytest
+
+
+@pytest.fixture
+def no_sleep(monkeypatch):
+    """Record backoff sleeps without actually waiting."""
+    sleeps: list[float] = []
+
+    async def fake_async_sleep(d):
+        sleeps.append(d)
+
+    monkeypatch.setattr(asyncio, "sleep", fake_async_sleep)
+    monkeypatch.setattr(time, "sleep", lambda d: sleeps.append(d))
+    return sleeps

libs/sdk-py/tests/test_auth.py

@@ -1,8 +1,49 @@
+import ast
+import inspect
+
 import pytest
 
 from langgraph_sdk import Auth
 
 
+@pytest.mark.parametrize(
+    "kwargs",
+    [{}, {"actions": "read"}, {"resources": None}],
+)
+def test_global_handler_factory_accepts_optional_resources(kwargs) -> None:
+    auth = Auth()
+    tree = ast.parse(inspect.getsource(type(auth.on)))
+    cls = tree.body[0]
+    assert isinstance(cls, ast.ClassDef)
+    factory_overload = next(
+        node
+        for node in cls.body
+        if isinstance(node, ast.FunctionDef)
+        and node.name == "__call__"
+        and node.decorator_list
+        and any(arg.arg == "resources" for arg in node.args.kwonlyargs)
+    )
+    resources = next(
+        arg for arg in factory_overload.args.kwonlyargs if arg.arg == "resources"
+    )
+    assert resources.annotation is not None
+    assert ast.unparse(resources.annotation) == "str | Sequence[str] | None"
+    default = factory_overload.args.kw_defaults[0]
+    assert isinstance(default, ast.Constant) and default.value is None
+
+    @auth.on(**kwargs)
+    async def handler(ctx, value):
+        del ctx, value
+        return None
+
+    if kwargs.get("actions"):
+        assert auth._handlers == {("*", "read"): [handler]}
+        assert auth._global_handlers == []
+    else:
+        assert auth._global_handlers == [handler]
+        assert auth._handlers == {}
+
+
 def test_handler_multiple_resources_and_actions() -> None:
     auth = Auth()
 

libs/sdk-py/tests/test_client_stream.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from collections.abc import Iterator, Sequence
+from collections.abc import Callable, Iterator, Sequence
 from pathlib import Path
 from typing import Any
 
@@ -13,6 +13,7 @@ from langgraph_sdk._async.runs import _wrap_stream_v2
 from langgraph_sdk._shared.utilities import _sse_to_v2_dict
 from langgraph_sdk._sync.runs import _wrap_stream_v2_sync
 from langgraph_sdk.client import HttpClient, SyncHttpClient
+from langgraph_sdk.errors import InternalServerError, NotFoundError
 from langgraph_sdk.schema import (
     CheckpointPayload,
     CheckpointsStreamPart,
@@ -130,6 +131,110 @@ def test_sse_decoder_strips_a_leading_bom():
     assert decoder.decode(b"") == StreamPart(event="values", data=1, id=None)  # ty: ignore[invalid-argument-type]
 
 
+def test_control_blocks_do_not_repeat_after_a_cursor_update():
+    decoder = SSEDecoder()
+    decoder.decode(b"id: cursor")
+    assert decoder.decode(b"") == StreamPart(event="", data=None, id="cursor")  # ty: ignore[invalid-argument-type]
+    decoder.decode(b": heartbeat")
+    assert decoder.decode(b"") is None
+    assert decoder.decode(b"") is None
+    decoder.decode(b"id:")
+    assert decoder.decode(b"") == StreamPart(event="", data=None, id=None)  # ty: ignore[invalid-argument-type]
+    assert decoder.last_event_id == ""
+    assert decoder.decode(b"") is None
+
+
+def test_cr_lines_are_emitted_without_waiting_for_another_chunk():
+    decoder = BytesLineDecoder()
+    assert decoder.decode(b"data: 1\r\r") == [b"data: 1", b""]
+    assert decoder.decode(b"\n") == []
+    assert decoder.decode(b"data: 2\r") == [b"data: 2"]
+    assert decoder.decode(b"") == []
+    assert decoder.decode(b"\n\r") == [b""]
+    assert decoder.flush() == []
+
+
+def test_empty_data_lines_preserve_their_newlines():
+    decoder = SSEDecoder()
+    for line in (b"data", b"data: 1", b"data:"):
+        decoder.decode(line)
+    assert decoder._data == b"\n1\n\n"
+    assert decoder.decode(b"") == StreamPart(event="", data=1, id=None)  # ty: ignore[invalid-argument-type]
+    decoder.decode(b"data:")
+    decoder.decode(b"data:")
+    assert decoder.decode(b"") == StreamPart(event="", data=None, id=None)  # ty: ignore[invalid-argument-type]
+    assert decoder.has_data
+    assert decoder.decode(b"") is None
+    assert not decoder.has_data
+
+
+def test_malformed_utf8_is_replaced_in_fields_and_json_strings():
+    decoder = SSEDecoder()
+    for line in (b"event: \xff", b"id: \xff", b'data: "\xff"'):
+        decoder.decode(line)
+    assert decoder.decode(b"") == StreamPart(event="\ufffd", data="\ufffd", id="\ufffd")  # ty: ignore[invalid-argument-type]
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+async def test_null_and_empty_data_are_not_dropped(asynchronous: bool):
+    def handler(_request: httpx.Request) -> httpx.Response:
+        return httpx.Response(
+            200,
+            headers={"Content-Type": "text/event-stream"},
+            content=b"data: null\n\ndata:\n\n",
+        )
+
+    transport = httpx.MockTransport(handler)
+    if asynchronous:
+        async with httpx.AsyncClient(
+            transport=transport, base_url="https://example.com"
+        ) as client:
+            parts = [part async for part in HttpClient(client).stream("/stream", "GET")]
+    else:
+        with httpx.Client(
+            transport=transport, base_url="https://example.com"
+        ) as client:
+            parts = list(SyncHttpClient(client).stream("/stream", "GET"))
+    assert parts == [StreamPart(event="", data=None), StreamPart(event="", data=None)]  # ty: ignore[invalid-argument-type]
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+async def test_cursor_is_inherited_after_reconnect(asynchronous: bool):
+    requests: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        requests.append(request)
+        if len(requests) == 1:
+            stream_cls = AsyncListByteStream if asynchronous else ListByteStream
+            return httpx.Response(
+                200,
+                headers={"Content-Type": "text/event-stream", "Location": "/reconnect"},
+                stream=stream_cls(
+                    [b"id: cursor\nevent: values\ndata: 1\n\n"],
+                    httpx.RemoteProtocolError("incomplete chunked read"),
+                ),
+            )
+        assert (b"Last-Event-ID", b"cursor") in request.headers.raw
+        return httpx.Response(
+            200,
+            headers={"Content-Type": "text/event-stream"},
+            content=b"event: values\ndata: 2\n\n",
+        )
+
+    transport = httpx.MockTransport(handler)
+    if asynchronous:
+        async with httpx.AsyncClient(
+            transport=transport, base_url="https://example.com"
+        ) as client:
+            parts = [part async for part in HttpClient(client).stream("/stream", "GET")]
+    else:
+        with httpx.Client(
+            transport=transport, base_url="https://example.com"
+        ) as client:
+            parts = list(SyncHttpClient(client).stream("/stream", "GET"))
+    assert [part.id for part in parts] == ["cursor", "cursor"]
+
+
 # --- HTTP client streaming ---
 
 
@@ -176,6 +281,7 @@ def test_sync_http_client_stream_flushes_trailing_event():
     assert parts == [StreamPart(event="foo", data={"bar": 1})]
 
 
+@pytest.mark.usefixtures("no_sleep")
 def test_sync_http_client_stream_recovers_after_disconnect():
     reconnect_path = "/reconnect"
     first_chunks = [
@@ -241,6 +347,7 @@ def test_sync_http_client_stream_recovers_after_disconnect():
 
 
 @pytest.mark.asyncio
+@pytest.mark.usefixtures("no_sleep")
 async def test_http_client_stream_recovers_after_disconnect():
     reconnect_path = "/reconnect"
     first_chunks = [
@@ -312,18 +419,14 @@ async def test_http_client_stream_recovers_after_disconnect():
     ]
 
 
-def _drop_after_an_empty_id(stream_cls: type, reconnects: list[httpx.Request]):
+def _drop_after(chunks: list[bytes], stream_cls: type, reconnects: list[httpx.Request]):
     def handler(request: httpx.Request) -> httpx.Response:
         if request.method == "POST":
             return httpx.Response(
                 200,
                 headers={"Content-Type": "text/event-stream", "Location": "/reconnect"},
                 stream=stream_cls(
-                    [
-                        b"id: 1\nevent: values\ndata: 1\n\n",
-                        b"id:\nevent: values\ndata: 2\n\n",
-                    ],
-                    httpx.RemoteProtocolError("incomplete chunked read"),
+                    chunks, httpx.RemoteProtocolError("incomplete chunked read")
                 ),
             )
         reconnects.append(request)
@@ -336,26 +439,409 @@ def _drop_after_an_empty_id(stream_cls: type, reconnects: list[httpx.Request]):
     return handler
 
 
-def test_sync_stream_reconnects_without_a_cursor_after_an_empty_id():
+def _sync_reconnect(
+    chunks: list[bytes], headers: dict[str, str] | None
+) -> httpx.Request:
     reconnects: list[httpx.Request] = []
-    transport = httpx.MockTransport(_drop_after_an_empty_id(ListByteStream, reconnects))
+    transport = httpx.MockTransport(_drop_after(chunks, ListByteStream, reconnects))
     with httpx.Client(transport=transport, base_url="https://example.com") as client:
-        list(SyncHttpClient(client).stream("/stream", "POST", json={}))
-
-    assert "last-event-id" not in reconnects[0].headers
+        list(SyncHttpClient(client).stream("/stream", "POST", json={}, headers=headers))
+    return reconnects[0]
 
 
-async def test_async_stream_reconnects_without_a_cursor_after_an_empty_id():
+async def _async_reconnect(
+    chunks: list[bytes], headers: dict[str, str] | None
+) -> httpx.Request:
     reconnects: list[httpx.Request] = []
     transport = httpx.MockTransport(
-        _drop_after_an_empty_id(AsyncListByteStream, reconnects)
+        _drop_after(chunks, AsyncListByteStream, reconnects)
     )
     async with httpx.AsyncClient(
         transport=transport, base_url="https://example.com"
     ) as client:
-        [part async for part in HttpClient(client).stream("/stream", "POST", json={})]
+        [
+            part
+            async for part in HttpClient(client).stream(
+                "/stream", "POST", json={}, headers=headers
+            )
+        ]
+    return reconnects[0]
 
-    assert "last-event-id" not in reconnects[0].headers
+
+_EMPTY_IDS = pytest.mark.parametrize(
+    "empty_id",
+    [b"id:\nevent: values\ndata: 2\n\n", b"id:\n\n"],
+    ids=["with-an-event", "alone"],
+)
+_CALLER_CURSORS = pytest.mark.parametrize(
+    "headers",
+    [None, {"Last-Event-ID": "5"}, {"last-event-id": "5"}],
+    ids=["no-caller-cursor", "caller-cursor", "lowercase-caller-cursor"],
+)
+
+
+@_EMPTY_IDS
+@_CALLER_CURSORS
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_stream_reconnects_without_a_cursor_after_an_empty_id(
+    empty_id: bytes, headers: dict[str, str] | None
+):
+    with pytest.warns(UserWarning, match="Last-Event-ID"):
+        reconnect = _sync_reconnect(
+            [b"id: 1\nevent: values\ndata: 1\n\n", empty_id], headers
+        )
+
+    assert "last-event-id" not in reconnect.headers
+
+
+@_EMPTY_IDS
+@_CALLER_CURSORS
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_stream_reconnects_without_a_cursor_after_an_empty_id(
+    empty_id: bytes, headers: dict[str, str] | None
+):
+    with pytest.warns(UserWarning, match="Last-Event-ID"):
+        reconnect = await _async_reconnect(
+            [b"id: 1\nevent: values\ndata: 1\n\n", empty_id], headers
+        )
+
+    assert "last-event-id" not in reconnect.headers
+
+
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_stream_id_replaces_a_lowercase_caller_cursor():
+    reconnect = _sync_reconnect(
+        [b"id: 1\nevent: values\ndata: 1\n\n"], {"last-event-id": "5"}
+    )
+
+    assert reconnect.headers.get_list("last-event-id") == ["1"]
+
+
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_stream_id_replaces_a_lowercase_caller_cursor():
+    reconnect = await _async_reconnect(
+        [b"id: 1\nevent: values\ndata: 1\n\n"], {"last-event-id": "5"}
+    )
+
+    assert reconnect.headers.get_list("last-event-id") == ["1"]
+
+
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_stream_keeps_the_caller_cursor_until_the_stream_sends_an_id():
+    reconnect = _sync_reconnect([b"event: values\ndata: 1\n\n"], {"Last-Event-ID": "5"})
+
+    assert reconnect.headers.get_list("last-event-id") == ["5"]
+
+
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_stream_keeps_the_caller_cursor_until_the_stream_sends_an_id():
+    reconnect = await _async_reconnect(
+        [b"event: values\ndata: 1\n\n"], {"Last-Event-ID": "5"}
+    )
+
+    assert reconnect.headers.get_list("last-event-id") == ["5"]
+
+
+# A reconnect that sends no Last-Event-ID can't replay what was sent while it was
+# disconnected, so it warns.
+_RECONNECT_CURSORS = pytest.mark.parametrize(
+    ("chunks", "headers", "warns"),
+    [
+        ([b"event: values\ndata: 1\n\n"], None, True),
+        ([b"id: 1\nevent: values\ndata: 1\n\n"], None, False),
+        ([b"event: values\ndata: 1\n\n"], {"Last-Event-ID": "5"}, False),
+    ],
+    ids=["no-cursor", "stream-cursor", "caller-cursor"],
+)
+
+
+@_RECONNECT_CURSORS
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_reconnect_warns_only_without_a_cursor(
+    chunks: list[bytes],
+    headers: dict[str, str] | None,
+    warns: bool,
+    recwarn: pytest.WarningsRecorder,
+):
+    _sync_reconnect(chunks, headers)
+
+    assert any("Last-Event-ID" in str(w.message) for w in recwarn) is warns
+
+
+@_RECONNECT_CURSORS
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_reconnect_warns_only_without_a_cursor(
+    chunks: list[bytes],
+    headers: dict[str, str] | None,
+    warns: bool,
+    recwarn: pytest.WarningsRecorder,
+):
+    await _async_reconnect(chunks, headers)
+
+    assert any("Last-Event-ID" in str(w.message) for w in recwarn) is warns
+
+
+# --- reconnects survive a server restart or a deploy ---
+
+SSE = {"Content-Type": "text/event-stream"}
+DROP = httpx.RemoteProtocolError("incomplete chunked read")
+
+
+def _event(i: int) -> bytes:
+    return f"id: {i}\nevent: values\ndata: {i}\n\n".encode()
+
+
+def _scripted(steps: list[Callable[[httpx.Request], httpx.Response]]):
+    """Handler that plays one step per request and records each request."""
+    seen: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append(request)
+        if len(seen) > len(steps):
+            raise AssertionError("unexpected request")
+        return steps[len(seen) - 1](request)
+
+    return handler, seen
+
+
+def _ok(stream_cls, chunks, *, drop=False, location=None):
+    headers = dict(SSE)
+    if location:
+        headers["Location"] = location
+
+    def step(_request):
+        return httpx.Response(
+            200, headers=headers, stream=stream_cls(chunks, DROP if drop else None)
+        )
+
+    return step
+
+
+def _status(code):
+    return lambda request: httpx.Response(
+        code, json={"detail": "upstream"}, request=request
+    )
+
+
+def _connect_error(request):
+    raise httpx.ConnectError("[Errno 61] Connection refused", request=request)
+
+
+def _not_sse(request):
+    return httpx.Response(
+        200, headers={"Content-Type": "text/html"}, text="<html>", request=request
+    )
+
+
+def _transient_steps(stream_cls, failure):
+    """POST drops after event 1; first reconnect fails; second succeeds."""
+    return [
+        _ok(stream_cls, [_event(1)], drop=True, location="/reconnect"),
+        failure,
+        _ok(stream_cls, [_event(2), b"event: end\ndata: null\n\n"]),
+    ]
+
+
+def _long_stream_steps(stream_cls, drops):
+    """POST + `drops` reconnects, each delivering one event then dropping."""
+    steps = [_ok(stream_cls, [_event(0)], drop=True, location="/reconnect")]
+    for i in range(1, drops):
+        steps.append(_ok(stream_cls, [_event(i)], drop=True))
+    steps.append(_ok(stream_cls, [_event(drops), b"event: end\ndata: null\n\n"]))
+    return steps
+
+
+def _run_sync(steps):
+    handler, seen = _scripted(steps)
+    with httpx.Client(
+        transport=httpx.MockTransport(handler), base_url="https://example.com"
+    ) as client:
+        parts = list(SyncHttpClient(client).stream("/stream", "POST", json={}))
+    return parts, seen
+
+
+async def _run_async(steps):
+    sync_handler, seen = _scripted(steps)
+
+    async def handler(request):
+        return sync_handler(request)
+
+    async with httpx.AsyncClient(
+        transport=httpx.MockTransport(handler), base_url="https://example.com"
+    ) as client:
+        parts = [p async for p in HttpClient(client).stream("/stream", "POST", json={})]
+    return parts, seen
+
+
+FAILURES = {
+    "429": _status(429),
+    "502": _status(502),
+    "503": _status(503),
+    "connect_error": _connect_error,
+    "not_sse": _not_sse,
+}
+
+
+# A reconnect that hits a 429 / 502 / 503 / connect error / non-SSE body, then
+# succeeds, should recover.
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize("failure", FAILURES.values(), ids=FAILURES.keys())
+def test_sync_reconnect_recovers_from_transient_failure(failure):
+    parts, seen = _run_sync(_transient_steps(ListByteStream, failure))
+    assert [p.event for p in parts] == ["values", "values", "end"]
+    assert len(seen) == 3
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize("failure", FAILURES.values(), ids=FAILURES.keys())
+async def test_async_reconnect_recovers_from_transient_failure(failure):
+    parts, seen = await _run_async(_transient_steps(AsyncListByteStream, failure))
+    assert [p.event for p in parts] == ["values", "values", "end"]
+    assert len(seen) == 3
+
+
+# Any other 4xx on a reconnect won't go away by retrying, so it raises.
+
+
+def _client_error_steps(stream_cls):
+    return [
+        _ok(stream_cls, [_event(1)], drop=True, location="/reconnect"),
+        _status(404),
+    ]
+
+
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_reconnect_does_not_retry_a_client_error():
+    with pytest.raises(NotFoundError):
+        _run_sync(_client_error_steps(ListByteStream))
+
+
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_reconnect_does_not_retry_a_client_error():
+    with pytest.raises(NotFoundError):
+        await _run_async(_client_error_steps(AsyncListByteStream))
+
+
+# The first request isn't a reconnect, so it raises even when it names a Location.
+
+
+def _first_request_503(request):
+    return httpx.Response(
+        503,
+        headers={"Location": "/reconnect"},
+        json={"detail": "upstream"},
+        request=request,
+    )
+
+
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_first_request_failure_is_not_retried():
+    with pytest.raises(InternalServerError):
+        _run_sync([_first_request_503])
+
+
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_first_request_failure_is_not_retried():
+    with pytest.raises(InternalServerError):
+        await _run_async([_first_request_503])
+
+
+# A server that stays down gets five reconnects, backing off 1, 2, 4, 5 and 5s
+# (each plus up to 25% jitter), so about 20s, before the stream gives up. The
+# error it gives up with is caused by the last failure, so callers see why.
+
+GIVE_UP = "Exceeded maximum SSE reconnection attempts"
+
+
+def _server_down_steps(stream_cls):
+    return [
+        _ok(stream_cls, [_event(1)], drop=True, location="/reconnect"),
+        *[_status(502)] * 5,
+    ]
+
+
+def _assert_backed_off_for_about_20s(sleeps: list[float]) -> None:
+    assert len(sleeps) == 5
+    for slept, delay in zip(sleeps, [1, 2, 4, 5, 5], strict=True):
+        assert delay <= slept <= delay * 1.25
+
+
+def test_sync_reconnect_gives_up_after_five_backed_off_attempts(no_sleep):
+    with pytest.raises(httpx.TransportError, match=GIVE_UP) as exc_info:
+        _run_sync(_server_down_steps(ListByteStream))
+    assert isinstance(exc_info.value.__cause__, InternalServerError)
+    _assert_backed_off_for_about_20s(no_sleep)
+
+
+async def test_async_reconnect_gives_up_after_five_backed_off_attempts(no_sleep):
+    with pytest.raises(httpx.TransportError, match=GIVE_UP) as exc_info:
+        await _run_async(_server_down_steps(AsyncListByteStream))
+    assert isinstance(exc_info.value.__cause__, InternalServerError)
+    _assert_backed_off_for_about_20s(no_sleep)
+
+
+# A long stream that drops 6 times, each reconnect succeeding and making
+# progress, should not run out of attempts.
+
+
+@pytest.mark.usefixtures("no_sleep")
+def test_sync_long_stream_survives_many_spaced_out_drops():
+    parts, _ = _run_sync(_long_stream_steps(ListByteStream, drops=6))
+    assert [p.data for p in parts] == [0, 1, 2, 3, 4, 5, 6, None]
+
+
+@pytest.mark.usefixtures("no_sleep")
+async def test_async_long_stream_survives_many_spaced_out_drops():
+    parts, _ = await _run_async(_long_stream_steps(AsyncListByteStream, drops=6))
+    assert [p.data for p in parts] == [0, 1, 2, 3, 4, 5, 6, None]
+
+
+# Each reconnect resumes after the newest event the stream got, so a reconnect
+# loop on a resumable run replays only what it missed. A failed reconnect keeps
+# the cursor for the next one.
+RECONNECT_LOOPS = {
+    "progress_between_drops": (
+        lambda stream_cls: _long_stream_steps(stream_cls, drops=3),
+        [None, "0", "1", "2"],
+    ),
+    "failed_reconnect": (
+        lambda stream_cls: _transient_steps(stream_cls, _status(502)),
+        [None, "1", "1"],
+    ),
+}
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize(
+    ("steps", "cursors"), RECONNECT_LOOPS.values(), ids=RECONNECT_LOOPS.keys()
+)
+def test_sync_reconnect_loop_resumes_after_the_newest_event(steps, cursors):
+    _, seen = _run_sync(steps(ListByteStream))
+    assert [r.headers.get("last-event-id") for r in seen] == cursors
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize(
+    ("steps", "cursors"), RECONNECT_LOOPS.values(), ids=RECONNECT_LOOPS.keys()
+)
+async def test_async_reconnect_loop_resumes_after_the_newest_event(steps, cursors):
+    _, seen = await _run_async(steps(AsyncListByteStream))
+    assert [r.headers.get("last-event-id") for r in seen] == cursors
+
+
+# Reconnects should back off rather than hammer the server.
+
+
+def test_sync_reconnect_backs_off(no_sleep):
+    _run_sync(_long_stream_steps(ListByteStream, drops=2))
+    assert len(no_sleep) == 2 and all(d > 0 for d in no_sleep)
+
+
+async def test_async_reconnect_backs_off(no_sleep):
+    await _run_async(_long_stream_steps(AsyncListByteStream, drops=2))
+    assert len(no_sleep) == 2 and all(d > 0 for d in no_sleep)
 
 
 # --- _sse_to_v2_dict conversion ---

libs/sdk-py/tests/test_runs_client.py

@@ -1,7 +1,8 @@
 from __future__ import annotations
 
 import json
-from collections.abc import AsyncIterator, Iterator
+from collections.abc import AsyncIterator, Callable, Iterator, Sequence
+from typing import Any
 
 import httpx
 import pytest
@@ -24,7 +25,16 @@ class _BodyDropsMidRead(httpx.SyncByteStream, httpx.AsyncByteStream):
         raise httpx.ReadError("connection dropped")
 
 
-def _wait_handler(requests: list[httpx.Request]):
+def _done(_request: httpx.Request) -> httpx.Response:
+    return httpx.Response(200, json={"done": True})
+
+
+def _wait_handler(
+    requests: list[httpx.Request],
+    reconnects: Sequence[Callable[[httpx.Request], httpx.Response]] = (_done,),
+):
+    """POST drops mid-body; the reconnects answer from `reconnects` in order."""
+
     def handler(request: httpx.Request) -> httpx.Response:
         requests.append(request)
         if request.method == "POST":
@@ -33,7 +43,7 @@ def _wait_handler(requests: list[httpx.Request]):
                 headers={"Location": "/threads/t1/runs/r1/join"},
                 stream=_BodyDropsMidRead(),
             )
-        return httpx.Response(200, json={"done": True})
+        return reconnects[len(requests) - 2](request)
 
     return handler
 
@@ -46,6 +56,7 @@ def _assert_bodyless_get(request: httpx.Request) -> None:
     assert request.read() == b""
 
 
+@pytest.mark.usefixtures("no_sleep")
 def test_sync_wait_reconnects_with_a_bodyless_get():
     requests: list[httpx.Request] = []
     transport = httpx.MockTransport(_wait_handler(requests))
@@ -58,6 +69,7 @@ def test_sync_wait_reconnects_with_a_bodyless_get():
     _assert_bodyless_get(requests[1])
 
 
+@pytest.mark.usefixtures("no_sleep")
 async def test_async_wait_reconnects_with_a_bodyless_get():
     requests: list[httpx.Request] = []
     transport = httpx.MockTransport(_wait_handler(requests))
@@ -72,6 +84,89 @@ async def test_async_wait_reconnects_with_a_bodyless_get():
     _assert_bodyless_get(requests[1])
 
 
+def _connect_error(request: httpx.Request) -> httpx.Response:
+    raise httpx.ConnectError("[Errno 61] Connection refused", request=request)
+
+
+async def _wait(
+    handler: Callable[[httpx.Request], httpx.Response], *, asynchronous: bool
+) -> Any:
+    transport = httpx.MockTransport(handler)
+    if asynchronous:
+        async with httpx.AsyncClient(
+            transport=transport, base_url="https://example.com"
+        ) as client:
+            return await RunsClient(HttpClient(client)).wait("t1", "agent", input={})
+    with httpx.Client(transport=transport, base_url="https://example.com") as client:
+        return SyncRunsClient(SyncHttpClient(client)).wait("t1", "agent", input={})
+
+
+# What a server restart or a deploy looks like to the reconnect GET: each one is
+# retried after a backoff.
+RECONNECT_FAILURES = {
+    "429": lambda request: httpx.Response(429, request=request),
+    "503": lambda request: httpx.Response(503, request=request),
+    "connect_error": _connect_error,
+    "body_drops": lambda _request: httpx.Response(
+        200,
+        headers={"Location": "/threads/t1/runs/r1/join"},
+        stream=_BodyDropsMidRead(),
+    ),
+}
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize(
+    "failure", RECONNECT_FAILURES.values(), ids=RECONNECT_FAILURES.keys()
+)
+async def test_wait_retries_a_failed_reconnect_after_a_backoff(
+    failure, asynchronous, no_sleep
+):
+    requests: list[httpx.Request] = []
+    with pytest.warns(UserWarning, match="attempting reconnect"):
+        result = await _wait(
+            _wait_handler(requests, [failure, _done]), asynchronous=asynchronous
+        )
+
+    assert result == {"done": True}
+    assert len(requests) == 3
+    assert len(no_sleep) == 2 and min(no_sleep) >= 1, no_sleep
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize("asynchronous", [False, True])
+async def test_wait_raises_after_five_failed_reconnects(asynchronous):
+    requests: list[httpx.Request] = []
+    with (
+        pytest.warns(UserWarning, match="attempting reconnect"),
+        pytest.raises(httpx.HTTPStatusError, match="503"),
+    ):
+        await _wait(
+            _wait_handler(requests, [RECONNECT_FAILURES["503"]] * 5),
+            asynchronous=asynchronous,
+        )
+
+    assert len(requests) == 6
+
+
+@pytest.mark.usefixtures("no_sleep")
+@pytest.mark.parametrize("asynchronous", [False, True])
+async def test_wait_does_not_retry_a_client_error(asynchronous):
+    requests: list[httpx.Request] = []
+    with (
+        pytest.warns(UserWarning, match="attempting reconnect"),
+        pytest.raises(httpx.HTTPStatusError, match="404"),
+    ):
+        await _wait(
+            _wait_handler(
+                requests, [lambda request: httpx.Response(404, request=request)]
+            ),
+            asynchronous=asynchronous,
+        )
+
+    assert len(requests) == 2
+
+
 def test_sync_wait_raises_the_run_error():
     requests: list[httpx.Request] = []
 

libs/sdk-py/uv.lock

@@ -301,7 +301,7 @@ wheels = [
 
 [[package]]
 name = "langgraph"
-version = "1.2.17"
+version = "1.2.19"
 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" },