Apply suggestions from code review

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: mikeas1

src/a2a/server/context.py

@@ -21,5 +21,5 @@ class ServerCallContext(BaseModel):
 
     state: State = Field(default={})
     user: User = Field(default=UnauthenticatedUser())
-    requested_extensions: set[str] = Field(default=set())
-    activated_extensions: set[str] = Field(default=set())
+    requested_extensions: set[str] = Field(default_factory=set)
+    activated_extensions: set[str] = Field(default_factory=set)

tests/server/request_handlers/test_grpc_handler.py

@@ -320,9 +320,9 @@ def side_effect(request, context: ServerCallContext):
         assert isinstance(call_context, ServerCallContext)
         assert call_context.requested_extensions == {'foo', 'bar'}
 
-        mock_grpc_context.set_trailing_metadata.assert_called_once_with(
-            [(HTTP_EXTENSION_HEADER, 'foo'), (HTTP_EXTENSION_HEADER, 'baz')]
-        )
+        mock_grpc_context.set_trailing_metadata.assert_called_once()
+        called_metadata = mock_grpc_context.set_trailing_metadata.call_args.args[0]
+        assert set(called_metadata) == {(HTTP_EXTENSION_HEADER, 'foo'), (HTTP_EXTENSION_HEADER, 'baz')}
 
     @patch(
         'a2a.server.request_handlers.grpc_handler.DefaultCallContextBuilder.build'
@@ -364,6 +364,6 @@ async def side_effect(request, context: ServerCallContext):
         assert isinstance(call_context, ServerCallContext)
         assert call_context.requested_extensions == {'foo', 'bar'}
 
-        mock_grpc_context.set_trailing_metadata.assert_called_once_with(
-            [(HTTP_EXTENSION_HEADER, 'foo'), (HTTP_EXTENSION_HEADER, 'baz')]
-        )
+        mock_grpc_context.set_trailing_metadata.assert_called_once()
+        called_metadata = mock_grpc_context.set_trailing_metadata.call_args.args[0]
+        assert set(called_metadata) == {(HTTP_EXTENSION_HEADER, 'foo'), (HTTP_EXTENSION_HEADER, 'baz')}