Remaining crash root-causes and menu churn

[ZivDero]

Three trace-first items where the legacy fix was a workaround:

• animation ownership during rapid building damage-state changes (the legacy patch skipped work behind a corrupt-pointer heuristic);
• the infantry/harvester sequence that leaves stale radar tracking (a defensive guard exists; the root cause does not);
• the main menu's per-loop cursor hide/show churn and its slowdown, measured on the current backend before changing it.

References: Vinifera (spawner branch, 2b809d61) flame-spawn block frames - a related invariant for the damage-state item, reproducer hint only.