Cache-hit prefill can skip draft forward for the prefix while PD transfer still reads draft KV for that same prefix. CP HiCache therefore needs to persist draft/MTP KV alongside target KV instead of relying on whatever remains in the draft GPU pool.
Constraint: CP HiCache is host-only here; storage backends remain unsupported for CP shared KV.
Constraint: CP shared KV must keep owner-page semantics and avoid falling back to full KV on every rank.
Rejected: Recompute cached-prefix draft KV during prefill | loses the HiCache benefit and reintroduces the large hidden/KV footprint.
Rejected: Change PD transfer to skip draft prefix KV | decode still needs draft cache continuity for MTP acceptance.
Confidence: medium
Scope-risk: moderate
Directive: Keep target and draft CP HiCache metadata/load/write/evict paths in lockstep; changing one without the other can silently reduce MTP accept length.
Tested: Remote g0034 container /sgl-workspace/sglang-tai: python3 -m pytest -q test/registered/unit/managers/test_hicache_controller_cp.py test/registered/unit/mem_cache/test_cp_hicache_metadata.py => 58 passed, 3 warnings
Not-tested: Full multi-node HiCache+MTP serving benchmark and accept-length recovery.
Add validate_page_aligned_token_indices utility and apply it across
HiCache write/load paths, NSA indexer transfers, and CUDA direct copy
kernels to reject malformed (partial, misaligned, non-contiguous) page
groups before they reach native transfer code. Also validate supported
CP HiCache backend/layout combinations at server startup.
laoyao0822
ThomasX