fix: fixupOutputFieldList skips argument type fixup for builtin return types

Move fixupInputFieldList(entry.arguments) before the early continue for
builtin return types so that input object arguments are always resolved
regardless of the output field's return type.

Without this fix, any field returning a builtin type (String, Int, etc.)
that takes a nullable input object argument generates std::optional<T>
instead of std::unique_ptr<T> in the concept, causing a compile error.
Non-null input object arguments with an empty default ({}) crash
schemagen with std::out_of_range in shouldMoveInputField.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Rafał Hibner

src/SchemaLoader.cpp

@@ -254,6 +254,8 @@ void SchemaLoader::fixupOutputFieldList(OutputFieldList& fields,
 			entry.accessor = *accessor;
 		}
 
+		fixupInputFieldList(entry.arguments);
+
 		if (s_builtinTypes.find(entry.type) != s_builtinTypes.cend())
 		{
 			continue;
@@ -311,8 +313,6 @@ void SchemaLoader::fixupOutputFieldList(OutputFieldList& fields,
 				throw std::runtime_error(error);
 			}
 		}
-
-		fixupInputFieldList(entry.arguments);
 	}
 }
 

test/SchemaLoaderTests.cpp

@@ -83,12 +83,12 @@ TEST(SchemaGenCase, NullableInputArgOnBuiltinReturnField)
 	EXPECT_EQ(headerContent.find("std::optional<TestInput>"), std::string::npos)
 		<< "concept should NOT use std::optional<TestInput> for nullable input object argument";
 
-	// Also check the source file for consistent usage.
+	// Also check the source file uses the correct ModifiedArgument with Nullable.
 	const auto sourceContent = readFile(outDir.path() / "QueryObject.cpp");
 	ASSERT_FALSE(sourceContent.empty()) << "QueryObject.cpp should be generated";
 
-	EXPECT_NE(sourceContent.find("unique_ptr<TestInput>"), std::string::npos)
-		<< "resolver should use unique_ptr<TestInput>";
+	EXPECT_NE(sourceContent.find("ModifiedArgument<test::TestInput>"), std::string::npos)
+		<< "resolver should use ModifiedArgument<test::TestInput>";
 }
 
 // Regression test: run schemagen on a schema where a builtin-returning field