Roto model loading: keep the stale-load helper test-only

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RDvxCS8xcR28VArjzn1x7U

crates/engine/src/analysis/models.rs

@@ -67,6 +67,7 @@ impl Models {
 
     /// Activate a model that finished loading for the choice counted as `generation`; `false` (and the model is
     /// dropped) when the choice changed meanwhile.
+    #[cfg(test)]
     pub(crate) fn set_active_if_current(&self, task: Task, model: Loaded, generation: u64) -> bool {
         activate_if_current(self.lane(task), &self.face_model, task, model, generation)
     }