chore: rename DiffChannel/DiffDelta/DiffChainValue to Delta* across libs

Renames the diff-channel types to DeltaChannel, DeltaValue, and DeltaChainValue
for consistency with the settled naming convention.

libs/checkpoint-postgres/langgraph/checkpoint/postgres/__init__.py

@@ -438,7 +438,7 @@ class PostgresSaver(BasePostgresSaver):
         *,
         cur: Any = None,
     ) -> dict[str, Any]:
-        from langgraph.checkpoint.base import DiffChainValue
+        from langgraph.checkpoint.base import DeltaChainValue
 
         result: dict[str, Any] = {}
         for channel, current_payload in diff_channel_payloads.items():
@@ -469,7 +469,7 @@ class PostgresSaver(BasePostgresSaver):
                     break
 
             payloads.reverse()
-            result[channel] = DiffChainValue(
+            result[channel] = DeltaChainValue(
                 base=base, deltas=[p["d"] for p in payloads]
             )
         return result

libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py

@@ -399,7 +399,7 @@ class AsyncPostgresSaver(BasePostgresSaver):
         *,
         cur: Any,
     ) -> dict[str, Any]:
-        from langgraph.checkpoint.base import DiffChainValue
+        from langgraph.checkpoint.base import DeltaChainValue
 
         result: dict[str, Any] = {}
         for channel, current_payload in diff_channel_payloads.items():
@@ -430,7 +430,7 @@ class AsyncPostgresSaver(BasePostgresSaver):
                     break
 
             payloads.reverse()
-            result[channel] = DiffChainValue(
+            result[channel] = DeltaChainValue(
                 base=base, deltas=[p["d"] for p in payloads]
             )
         return result

libs/checkpoint-postgres/langgraph/checkpoint/postgres/base.py

@@ -223,7 +223,7 @@ class BasePostgresSaver(BaseCheckpointSaver[str]):
         *,
         cur: Any = None,
     ) -> dict[str, Any]:
-        """Override in sync/async subclasses. Resolves diff-chain blobs to DiffChainValue."""
+        """Override in sync/async subclasses. Resolves diff-chain blobs to DeltaChainValue."""
         raise NotImplementedError
 
     def _dump_blobs(

libs/checkpoint-postgres/tests/test_async.py

@@ -374,22 +374,22 @@ async def test_get_checkpoint_no_channel_values(
 
 
 @pytest.mark.parametrize("saver_name", ["base", "pool", "pipe"])
-async def test_diff_channel_chain_reconstruction(saver_name: str) -> None:
-    """AsyncPostgresSaver reconstructs DiffChannel chain via point-lookup traversal."""
+async def test_delta_channel_chain_reconstruction(saver_name: str) -> None:
+    """AsyncPostgresSaver reconstructs DeltaChannel chain via point-lookup traversal."""
     pytest.importorskip(
-        "langgraph.channels.diff", reason="langgraph core not installed"
+        "langgraph.channels.delta", reason="langgraph core not installed"
     )
 
     from typing import Annotated
 
     from langchain_core.messages import AIMessage, HumanMessage
-    from langgraph.channels.diff import DiffChannel
+    from langgraph.channels.delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
     from typing_extensions import TypedDict
 
     class State(TypedDict):
-        messages: Annotated[list, DiffChannel(add_messages)]
+        messages: Annotated[list, DeltaChannel(add_messages)]
 
     def respond(state: State) -> dict:
         n = len(state["messages"])