CP shared KV needs HiCache backup to overlap with layer execution without exposing partially copied host state. Split CP backup into reservation, pending radix state, per-layer target/draft D2H submission, and one final ack-driven visibility commit. The all-layer path remains available only as an explicit fallback and now logs a warning when used.
Constraint: CP shared KV owner-lane metadata and draft/MTP KV must stay strongly synchronized with target KV.
Constraint: Local CUDA tests are disallowed; CUDA verification was run only in the g0034 container.
Rejected: Let target layer hooks copy draft KV too | draft may not have stored that layer yet, which can corrupt MTP accept behavior.
Rejected: Silent all-layer fallback | it hides performance regressions and makes ETE logs ambiguous.
Confidence: medium
Scope-risk: broad
Directive: Reserved or partially copied host payloads must remain invisible until final ack commits pending_host_backups.
Tested: g0034 docker /sgl-workspace/sglang-tai PYTHONPATH=/mnt/beegfs/cjy/tai-kernel/python:python python -m pytest test/registered/unit/managers/test_hicache_controller_cp.py -q -> 49 passed.
Tested: g0034 docker /sgl-workspace/sglang-tai PYTHONPATH=/mnt/beegfs/cjy/tai-kernel/python:python python -m pytest test/registered/unit/mem_cache/test_cp_hicache_metadata.py -q -> 58 passed.
Tested: g0034 docker /mnt/beegfs/cjy/tai-kernel PYTHONPATH=python python -m pytest tests/nsa_prefill/test_kvcacheio_lf_pf.py -q -> 7 passed.
Not-tested: Long-running GLM5 CP+HiCache+MTP ETE throughput and host-pressure soak.
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