fix(sdk): preserve decrypt handler types

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

@@ -18,6 +18,9 @@ import warnings
 
 from langgraph_sdk.encryption import types
 
+_BlobDecryptorT = typing.TypeVar("_BlobDecryptorT", bound=types.BlobDecryptor)
+_JsonDecryptorT = typing.TypeVar("_JsonDecryptorT", bound=types.JsonDecryptor)
+
 
 class LangGraphBetaWarning(UserWarning):
     """Warning for beta features in LangGraph SDK."""
@@ -141,7 +144,7 @@ class _DecryptDecorators:
     def __init__(self, parent: Encryption):
         self._parent = parent
 
-    def blob(self, fn: types.BlobDecryptor) -> types.BlobDecryptor:
+    def blob(self, fn: _BlobDecryptorT) -> _BlobDecryptorT:
         """Register a blob decryption handler.
 
         The handler will be called to decrypt opaque data like checkpoint blobs.
@@ -172,7 +175,7 @@ class _DecryptDecorators:
         self._parent._blob_decryptor = fn
         return fn
 
-    def json(self, fn: types.JsonDecryptor) -> types.JsonDecryptor:
+    def json(self, fn: _JsonDecryptorT) -> _JsonDecryptorT:
         """Register the JSON decryption handler.
 
         Example:

libs/sdk-py/tests/test_encryption.py

@@ -1,6 +1,8 @@
+from collections.abc import Awaitable, Callable
+
 import pytest
 
-from langgraph_sdk import DecryptResult
+from langgraph_sdk import DecryptResult, EncryptionContext
 from langgraph_sdk.encryption import DuplicateHandlerError, Encryption
 
 
@@ -12,6 +14,27 @@ def test_decrypt_result():
     assert DecryptResult(plaintext={"plain": True}).replacement is None
 
 
+def test_decrypt_decorators_preserve_return_types():
+    encryption = Encryption()
+
+    @encryption.decrypt.blob
+    async def blob_dec(_ctx: EncryptionContext, data: bytes) -> bytes:
+        return data
+
+    @encryption.decrypt.json
+    async def json_dec(
+        _ctx: EncryptionContext, data: dict[str, object]
+    ) -> dict[str, object]:
+        return data
+
+    blob_handler: Callable[[EncryptionContext, bytes], Awaitable[bytes]] = blob_dec
+    json_handler: Callable[
+        [EncryptionContext, dict[str, object]], Awaitable[dict[str, object]]
+    ] = json_dec
+    assert blob_handler is blob_dec
+    assert json_handler is json_dec
+
+
 class TestHandlerValidation:
     """Test duplicate handler and signature validation."""