clip_grad_norm now returns a GPU-resident Tensor instead of (f64, f64),
keeping backward → clip → optimizer.step fully pipelined on GPU with
zero cuStreamSynchronize stalls. The unconditional multiply trick
(scale = min(max_norm/(norm+eps), 1.0)) avoids the conditional branch
that previously required reading the norm to CPU.
Key changes:
- gradient_utils::clip_grad_norm: return Tensor, unconditional GPU multiply
- Handle BF16 mixed-precision via per-gradient to_dtype cast
- adam.rs: backward_step_with_monitoring returns Tensor (zero sync)
- gradient_accumulation: delegate to gradient_utils (DRY, same GPU path)
- dqn.rs: single sync boundary after ALL GPU work queued
1746 tests passing (ml-core 286, ml-dqn 388, ml-ppo 198, ml 874).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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