Removed 19 diagnostic eprintln + 7 stream.synchronize() calls that were
added during H100 hang debugging. All hang root causes are now fixed:
- grad_norm atomicAdd → two-phase reduction
- vaccine dot+norm atomicAdd → two-phase reduction
- C51 mixup spin-wait barrier → split into two kernels
Zero diagnostic overhead in the training hot loop.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>