MOAD-0005 (Thundering Herd): CLEAN

All caches with multi-threaded access use proper synchronization:
- Module symbol cache (module.cc): global_critical_region_ Acquire() wraps
  all map_.find() + map_[] insert operations.
- GPU pipeline/shader cache (pipeline_cache.cc): accessed from single GPU
  command thread; no concurrent writers.
- Object table (object_table.cc): global_critical_region_ wraps all slot
  accesses.
No unsynchronized check-then-act cache patterns found.
