Use DefaultSerde instead of JsonSerde for promise() default parameter

python/restate/server_context.py

@@ -47,7 +47,7 @@
 )
 from restate.exceptions import TerminalError, SdkInternalBaseException, SdkInternalException, SuspendedException
 from restate.handler import Handler, handler_from_callable, invoke_handler
-from restate.serde import BytesSerde, DefaultSerde, JsonSerde, Serde
+from restate.serde import BytesSerde, DefaultSerde, Serde
 from restate.server_types import ReceiveChannel, Send
 from restate.vm import Failure, Invocation, NotReady, VMWrapper, RunRetryConfig, Suspended  # pylint: disable=line-too-long
 from restate.vm import (
@@ -939,7 +939,7 @@ def reject_awakeable(self, name: str, failure_message: str, failure_code: int =
         update_restate_context_is_replaying(self.vm)
 
     def promise(
-        self, name: str, serde: typing.Optional[Serde[T]] = JsonSerde(), type_hint: Optional[typing.Type[T]] = None
+        self, name: str, serde: typing.Optional[Serde[T]] = DefaultSerde(), type_hint: Optional[typing.Type[T]] = None
     ) -> DurablePromise[T]:
         """Create a durable promise."""
         if isinstance(serde, DefaultSerde):

tests/servercontext.py

@@ -18,7 +18,9 @@
     TerminalError,
     VirtualObject,
     Workflow,
+    WorkflowContext,
 )
+from restate.serde import DefaultSerde
 import pytest
 import typing
 
@@ -74,3 +76,22 @@ async def greet(ctx: Context, name: str) -> str:
     async with simple_harness(greeter) as client:
         with pytest.raises(Exception):
             await client.service_call(greet, arg="bob")
+
+
+async def test_promise_default_serde():
+    workflow = Workflow("test_workflow")
+
+    @workflow.main()
+    async def run(ctx: WorkflowContext) -> str:
+        promise = ctx.promise("test.promise", type_hint=str)
+
+        assert isinstance(promise.serde, DefaultSerde), \
+            f"Expected DefaultSerde but got {type(promise.serde).__name__}"
+
+        await promise.resolve("success")
+        return await promise.value()
+
+
+    async with simple_harness(workflow) as client:
+        result = await client.workflow_call(run, key="test-key", arg=None)
+        assert result == "success"