result->deleted_context = tail_to_core_usv(km_core_state_app_context(state), result->code_points_to_delete);

should be added in km_core_state_get_actions immediately before updating app context.

   km_core_actions * result = action_item_list_to_actions_object(action_items);
+
+  result->deleted_context = tail_to_core_usv(km_core_state_app_context(state), result->code_points_to_delete);

   if(state->processor().supports_normalization()) {

This must also be disposed correctly.

This makes it easier for consumers to figure out surrogate pairs etc (or utf-8 if necessary), and is a nice string to work with for unit tests.