Checkpoint 4: harden native paths, authoring workflows and Player lifecycle

include/faset/runtime/schema.hpp

@@ -0,0 +1,17 @@
+#pragma once
+#include <nlohmann/json_fwd.hpp>
+#include <string_view>
+
+namespace faset::runtime {
+// Exact native TypeIds. A prefix alone does not make a custom type native.
+bool is_builtin_component(std::string_view type) noexcept;
+
+// Player boundary: require every custom TypeId and its exact positive integer
+// version in the linked gameplay schema. Accepts its array or a {types:[...]}
+// manifest. Native components always require version 1. A missing version means
+// 1 for existing development scenes. Gameplay may not redeclare native TypeIds.
+// Does not migrate or change source data.
+// Structural/native field checks remain Runtime::load's responsibility; this
+// function has no authoring dependency and runs no gameplay callbacks.
+void validate_scene_schemas(const nlohmann::json& scene, const nlohmann::json& gameplay_schema);
+} // namespace faset::runtime