chore(internal): update base client (#197)

src/modern_treasury/_base_client.py

@@ -24,7 +24,7 @@
     overload,
 )
 from functools import lru_cache
-from typing_extensions import Literal, get_origin
+from typing_extensions import Literal, get_args, get_origin
 
 import anyio
 import httpx
@@ -458,6 +458,14 @@ def _serialize_multipartform(self, data: Mapping[object, object]) -> dict[str, o
             serialized[key] = value
         return serialized
 
+    def _extract_stream_chunk_type(self, stream_cls: type) -> type:
+        args = get_args(stream_cls)
+        if not args:
+            raise TypeError(
+                f"Expected stream_cls to have been given a generic type argument, e.g. Stream[Foo] but received {stream_cls}",
+            )
+        return cast(type, args[0])
+
     def _process_response(
         self,
         *,
@@ -793,7 +801,10 @@ def _request(
             raise APIConnectionError(request=request) from err
 
         if stream:
-            stream_cls = stream_cls or cast("type[_StreamT] | None", self._default_stream_cls)
+            if stream_cls:
+                return stream_cls(cast_to=self._extract_stream_chunk_type(stream_cls), response=response, client=self)
+
+            stream_cls = cast("type[_StreamT] | None", self._default_stream_cls)
             if stream_cls is None:
                 raise MissingStreamClassError()
             return stream_cls(cast_to=cast_to, response=response, client=self)
@@ -1156,7 +1167,10 @@ async def _request(
             raise APIConnectionError(request=request) from err
 
         if stream:
-            stream_cls = stream_cls or cast("type[_AsyncStreamT] | None", self._default_stream_cls)
+            if stream_cls:
+                return stream_cls(cast_to=self._extract_stream_chunk_type(stream_cls), response=response, client=self)
+
+            stream_cls = cast("type[_AsyncStreamT] | None", self._default_stream_cls)
             if stream_cls is None:
                 raise MissingStreamClassError()
             return stream_cls(cast_to=cast_to, response=response, client=self)