refactor(langgraph): check for put_writes' task_path in one place

Both loop setups and bulk_update_state inspected the saver's signature
themselves; they now share put_writes_accepts_task_path.

libs/langgraph/langgraph/pregel/_checkpoint.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import uuid
 from collections.abc import Callable, Iterable, Mapping
 from datetime import datetime, timezone
+from inspect import signature
 from typing import Any, Literal, cast
 
 from langchain_core.runnables import RunnableConfig
@@ -49,6 +50,15 @@ def empty_checkpoint() -> Checkpoint:
     )
 
 
+def put_writes_accepts_task_path(put_writes: Callable[..., Any]) -> bool:
+    """Whether a saver's `put_writes` or `aput_writes` takes `task_path`.
+
+    Savers written before the parameter existed don't, so it is passed only
+    when this is true.
+    """
+    return signature(put_writes).parameters.get("task_path") is not None
+
+
 def exit_delta_task_id(step: int, task_id: str) -> str:
     """Synthetic task id for exit-mode DeltaChannel writes.
 

libs/langgraph/langgraph/pregel/_loop.py

@@ -12,7 +12,6 @@ from contextlib import (
     ExitStack,
 )
 from datetime import datetime, timezone
-from inspect import signature
 from types import TracebackType
 from typing import (
     Any,
@@ -107,6 +106,7 @@ from langgraph.pregel._checkpoint import (
     delta_channels_with_pending_writes,
     empty_checkpoint,
     exit_delta_task_id,
+    put_writes_accepts_task_path,
 )
 from langgraph.pregel._executor import (
     AsyncBackgroundExecutor,
@@ -1584,8 +1584,7 @@ class SyncPregelLoop(PregelLoop, AbstractContextManager):
             self.checkpointer_get_next_version = checkpointer.get_next_version
             self.checkpointer_put_writes = checkpointer.put_writes
             self.checkpointer_put_writes_accepts_task_path = (
-                signature(checkpointer.put_writes).parameters.get("task_path")
-                is not None
+                put_writes_accepts_task_path(checkpointer.put_writes)
             )
         else:
             self.checkpointer_get_next_version = increment
@@ -1840,8 +1839,7 @@ class AsyncPregelLoop(PregelLoop, AbstractAsyncContextManager):
             self.checkpointer_get_next_version = checkpointer.get_next_version
             self.checkpointer_put_writes = checkpointer.aput_writes
             self.checkpointer_put_writes_accepts_task_path = (
-                signature(checkpointer.aput_writes).parameters.get("task_path")
-                is not None
+                put_writes_accepts_task_path(checkpointer.aput_writes)
             )
         else:
             self.checkpointer_get_next_version = increment

libs/langgraph/langgraph/pregel/main.py

@@ -19,7 +19,7 @@ from collections.abc import (
 from dataclasses import is_dataclass, replace
 from datetime import timedelta
 from functools import partial
-from inspect import isclass, signature
+from inspect import isclass
 from typing import (
     Any,
     Generic,
@@ -140,6 +140,7 @@ from langgraph.pregel._checkpoint import (
     delta_channels_with_pending_writes,
     empty_checkpoint,
     get_updated_channels_from_tasks,
+    put_writes_accepts_task_path,
     versions_seen_without_bumps,
 )
 from langgraph.pregel._draw import draw_graph
@@ -4250,7 +4251,7 @@ def _task_path_kwarg(put_writes: Callable[..., Any], task: PregelTaskWrites) ->
     Savers that replay a checkpoint's writes in task path order then give back
     updates applied together in the order they were given.
     """
-    if signature(put_writes).parameters.get("task_path") is None:
+    if not put_writes_accepts_task_path(put_writes):
         return {}
     return {"task_path": task_path_str(task.path)}