CP HiCache direct/page_first_direct all-layer backup was still able to enter sgl-kernel's stale cudaMemcpyBatchAsync path, which segfaults under CUDA 13 before Python can surface an error. The SGLang route now avoids that all-layer sgl-kernel op for page_first_direct backup and uses the TAI per-layer direct LF->PF op for MHA, MLA, and NSA indexer data.\n\nThe load-back path also prepares NSA indexer page indices once per load op and reuses them across per-layer H2D loads, preserving per-layer overlap while removing redundant page-index derivation.\n\nConstraint: Remote runtime is CUDA 13.0 where sgl-kernel's all-layer direct LF->PF op uses the wrong cudaMemcpyBatchAsync ABI.\nRejected: Patch sgl-kernel in this branch | we are converging production HiCache direct/page_first_direct paths onto tai-kernel and do not want to maintain another CUDA-ABI-sensitive copy path here.\nRejected: Collapse H2D load-back into one all-layer op | that would reduce submit count but lose per-layer completion visibility and forward overlap.\nConfidence: medium\nScope-risk: moderate\nDirective: Do not reintroduce sgl_kernel.transfer_kv_all_layer_direct_lf_pf for direct/page_first_direct HiCache backup without CUDA 13 ABI verification.\nTested: g0034 container: PYTHONPATH=python python -m pytest -q -s test/registered/unit/mem_cache/test_nsa_pool_host_unit.py -> 10 passed, 3 warnings.\nTested: g0034 container: PYTHONPATH=python python -m pytest -q test/registered/unit/managers/test_hicache_controller_cp.py -> 61 passed, 3 warnings.\nTested: python -m py_compile python/sglang/srt/mem_cache/memory_pool_host.py python/sglang/srt/managers/cache_controller.py test/registered/unit/mem_cache/test_nsa_pool_host_unit.py test/registered/unit/managers/test_hicache_controller_cp.py\nNot-tested: Full ETE prefill/decode traffic after this commit.\nNot-tested: sgl-kernel implementation itself remains unchanged.
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