Implements per-layer KV push during prefill (write mode) on vLLM's
MooncakeConnector, env-gated by MOONCAKE_LAYERWISE=1. 2-instance microbench
(mb7) shows correctness (KV lands, cached==prompt) and that the transfer is
hidden behind prefill compute: critical-path overhead drops from O(KV size)
(123/202/529ms for 8k/16k/32k) to a flat ~58ms (2-9x), with no prefill
slowdown, on idle instances. Caveats: idle-only, chunked-prefill disabled,
single concurrent transfer — see DESIGN.md.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
