Capture complete gameplay and toolchain build inputs

include/faset/editor/build_cache.hpp

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <faset/editor/build_service.hpp>
+#include <faset/scripting/project.hpp>
+#include <filesystem>
+#include <string>
+
+namespace faset::editor {
+
+struct BuildInputs {
+    std::string source_hash;
+    std::string recipe_hash;
+    std::string toolchain_hash;
+    std::string fingerprint() const;
+};
+
+// Hash all files in Scripts and the active Lua declaration, not only the two
+// conventional gameplay files. Both Editor stale-state and builds use this key.
+std::string gameplay_source_hash(const std::filesystem::path& project_root,
+                                 const scripting::LuaProject& lua);
+BuildInputs capture_build_inputs(const BuildConfig& config, const scripting::LuaProject& lua);
+
+// A compiler replaced at the same path may be invisible to Ninja. Invalidate
+// only this generated native tree; published build generations stay intact.
+void ensure_native_toolchain_stamp(const std::filesystem::path& native_directory,
+                                   const BuildInputs& inputs);
+
+} // namespace faset::editor