Run init.ds from engineInit once every other system is ready

assets/init.ds is compiled and packed as init.dsb like any other script, and
engineInit() runs it as the very last init step - after scriptInit() and
sceneInit(), right before the initial scene is set - so it's free to use any
engine system (display, audio, save, rpg, ui, scenes, ...) without having to
special-case startup ordering. A syntax error or runtime failure in init.ds
is fatal, same as every other errorChain()'d init step.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

assets/init.ds

@@ -0,0 +1 @@
+// Entry point, run once by the engine after every other system is ready.

src/dusk/engine/engine.c

@@ -56,6 +56,12 @@ errorret_t engineInit(const int32_t argc, const char_t **argv) {
   errorChain(scriptInit());
   errorChain(sceneInit());
 
+  // Runs once every other system is ready, so init.ds can use any of them.
+  scripterror_t scriptInitError;
+  if(scriptRuntimeRunFile(SCRIPT.runtime, "init.dsb", false, &scriptInitError) != SCRIPT_OK) {
+    errorThrow("init.ds failed: %s", scriptInitError.message);
+  }
+
   consolePrint("Engine initialized");
 
   #ifdef DUSK_ASSERTIONS_FAKED