refactor(channels): extract _operators_equal helper, deduplicate __eq__ logic

Both BinaryOperatorAggregate and DeltaChannel had identical inline logic for
comparing operators that may be lambdas. Extract _operators_equal into
binop.py (alongside _get_overwrite) and use it in both __eq__ methods.

Also removes the duplicate _get_overwrite definition from delta.py — it was
identical to binop.py's and is now imported from there instead, along with
the now-unused OVERWRITE constant and Overwrite imports.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

libs/langgraph/langgraph/channels/binop.py

@@ -37,6 +37,17 @@ def _get_overwrite(value: Any) -> tuple[bool, Any]:
     return False, None
 
 
+def _operators_equal(a: Callable, b: Callable) -> bool:
+    """Return True if two reducer operators should be considered equal.
+
+    Lambdas all share the name '<lambda>' so identity comparison is
+    unreliable; treat any pairing that includes a lambda as equal.
+    """
+    if a.__name__ == "<lambda>" or b.__name__ == "<lambda>":
+        return True
+    return a is b
+
+
 class BinaryOperatorAggregate(Generic[Value], BaseChannel[Value, Value, Value]):
     """Stores the result of applying a binary operator to the current value and each new value.
 
@@ -67,11 +78,8 @@ class BinaryOperatorAggregate(Generic[Value], BaseChannel[Value, Value, Value]):
             self.value = MISSING
 
     def __eq__(self, value: object) -> bool:
-        return isinstance(value, BinaryOperatorAggregate) and (
-            value.operator is self.operator
-            if value.operator.__name__ != "<lambda>"
-            and self.operator.__name__ != "<lambda>"
-            else True
+        return isinstance(value, BinaryOperatorAggregate) and _operators_equal(
+            self.operator, value.operator
         )
 
     @property

libs/langgraph/langgraph/channels/delta.py

@@ -8,16 +8,15 @@ from langgraph.checkpoint.base import DELTA_SENTINEL, PendingWrite
 from langgraph.checkpoint.serde.types import _DeltaSnapshot
 from typing_extensions import Self
 
-from langgraph._internal._constants import OVERWRITE
 from langgraph._internal._typing import MISSING
 from langgraph.channels.base import BaseChannel, Value
+from langgraph.channels.binop import _get_overwrite, _operators_equal
 from langgraph.errors import (
     EmptyChannelError,
     ErrorCode,
     InvalidUpdateError,
     create_error_message,
 )
-from langgraph.types import Overwrite
 
 __all__ = ("DeltaChannel",)
 
@@ -29,14 +28,6 @@ def _empty(typ: Any) -> Any:
         return []
 
 
-def _get_overwrite(value: Any) -> tuple[bool, Any]:
-    if isinstance(value, Overwrite):
-        return True, value.value
-    if isinstance(value, dict) and set(value.keys()) == {OVERWRITE}:
-        return True, value[OVERWRITE]
-    return False, None
-
-
 class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
     """Fold-reducer channel with configurable snapshot cadence.
 
@@ -74,12 +65,7 @@ class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
             return False
         if self.snapshot_frequency != other.snapshot_frequency:
             return False
-        if (
-            self.operator.__name__ != "<lambda>"
-            and other.operator.__name__ != "<lambda>"
-        ):
-            return self.operator is other.operator
-        return True
+        return _operators_equal(self.operator, other.operator)
 
     @property
     def ValueType(self) -> Any: