fix: stream part generic order (#7134)

this is technically breaking but is a fix given dependency of output t
on state t

libs/langgraph/langgraph/pregel/main.py

@@ -2456,7 +2456,7 @@ class Pregel(
         debug: bool | None = None,
         version: Literal["v2"],
         **kwargs: Unpack[DeprecatedKwargs],
-    ) -> Iterator[StreamPart[OutputT, StateT]]: ...
+    ) -> Iterator[StreamPart[StateT, OutputT]]: ...
 
     @overload
     def stream(
@@ -2787,7 +2787,7 @@ class Pregel(
         debug: bool | None = None,
         version: Literal["v2"],
         **kwargs: Unpack[DeprecatedKwargs],
-    ) -> AsyncIterator[StreamPart[OutputT, StateT]]: ...
+    ) -> AsyncIterator[StreamPart[StateT, OutputT]]: ...
 
     @overload
     def astream(
@@ -3194,7 +3194,7 @@ class Pregel(
         durability: Durability | None = None,
         version: Literal["v2"],
         **kwargs: Any,
-    ) -> list[StreamPart[OutputT, StateT]]: ...
+    ) -> list[StreamPart[StateT, OutputT]]: ...
 
     @overload
     def invoke(
@@ -3364,7 +3364,7 @@ class Pregel(
         durability: Durability | None = None,
         version: Literal["v2"],
         **kwargs: Any,
-    ) -> list[StreamPart[OutputT, StateT]]: ...
+    ) -> list[StreamPart[StateT, OutputT]]: ...
 
     @overload
     async def ainvoke(

libs/langgraph/langgraph/pregel/protocol.py

@@ -117,7 +117,7 @@ class PregelProtocol(Runnable[InputT, Any], Generic[StateT, ContextT, InputT, Ou
         interrupt_after: All | Sequence[str] | None = None,
         subgraphs: bool = False,
         version: Literal["v2"],
-    ) -> Iterator[StreamPart[OutputT, StateT]]: ...
+    ) -> Iterator[StreamPart[StateT, OutputT]]: ...
 
     @overload
     @abstractmethod
@@ -161,7 +161,7 @@ class PregelProtocol(Runnable[InputT, Any], Generic[StateT, ContextT, InputT, Ou
         interrupt_after: All | Sequence[str] | None = None,
         subgraphs: bool = False,
         version: Literal["v2"],
-    ) -> AsyncIterator[StreamPart[OutputT, StateT]]: ...
+    ) -> AsyncIterator[StreamPart[StateT, OutputT]]: ...
 
     @overload
     @abstractmethod

libs/langgraph/langgraph/types.py

@@ -335,7 +335,7 @@ StreamPart = TypeAliasType(
     | CheckpointStreamPart[StateT]
     | TasksStreamPart
     | DebugStreamPart[StateT],
-    type_params=(OutputT, StateT),
+    type_params=(StateT, OutputT),
 )
 """A discriminated union of all v2 stream part types.
 

libs/langgraph/tests/test_stream_v2.py

@@ -1129,7 +1129,7 @@ _OutputT = TypeVar("_OutputT")
 _StateT = TypeVar("_StateT")
 
 
-def _check_type_narrowing(part: StreamPart[_OutputT, _StateT]) -> None:
+def _check_type_narrowing(part: StreamPart[_StateT, _OutputT]) -> None:
     """Compile-time type narrowing checks — never called at runtime."""
     if part["type"] == "values":
         assert_type(part, ValuesStreamPart[_OutputT])