feat(ml): GPU saturation backlog — PPO rollout sync, VRAM-aware dims, KAN GPU splines
Three remaining GPU bottlenecks from the saturation backlog:
1. PPO rollout GPU sync stalls (3→1 per step):
- Merged sample_action to return (action_idx, probs_vec), eliminating
duplicate to_vec1 sync on action probabilities
- Batched critic forward after rollout loop — single GPU→CPU sync
replaces per-step critic.forward() calls (2048 syncs → 1)
- Safe indexing throughout (clippy deny rules)
2. VRAM-aware default network dimensions:
- Added detect_vram_mb() with GPU_MEMORY_MB env var override for K8s
- Added vram_scaled_hidden_dims() with 4 tiers (CPU/<8GB/16GB/40GB+)
- DQN: [256,256] → [2048,1024,512] on L40S/H100
- PPO: hidden_dim_base 128 → 1024 on L40S/H100
- Wired into train_baseline_rl.rs for non-hyperopt training runs
3. KAN B-spline GPU lookup table:
- Pre-compute basis values on 1024-point grid at layer construction
- GPU evaluation via gather + linear interpolation (replaces recursive
Cox-de Boor CPU bounce: 32K recursive calls → 2 GPU gathers)
- Fallback to CPU path when grid not pre-computed
5 files changed, +687/-43, 2476 tests pass, 0 clippy warnings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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