The index path now mirrors the target MLA partial-current contract: prefetched or synchronously materialized prefix pages are composed with valid current index K/scale rows in slot-dense page buffers. Current-only batches keep the compact current-index fast path, while partial cache-hit batches share one composed dense index buffer across the in-seq prev/next topk pair.\n\nThe prefetch consume path remaps through the slot page inverse instead of treating the slot-dense buffer as physical-pool capacity, and current-index quantization uses valid extend rows so padded out_cache_loc does not disable reuse.\n\nConstraint: CP shared KV remains page-slot based; padding rows must stay invisible to attention/index semantics\nConstraint: Draft/EAGLE partial-current reuse remains guarded by should_reuse_current_extend_kv\nRejected: Replace prefix all-reduce with all-gather | NCCL all-gather still uses SM and would require an additional compose/scatter step\nConfidence: medium\nScope-risk: moderate\nDirective: Do not reintroduce current-only gating for index reuse; partial target cache hits must compose prefix + valid current rows\nTested: Local py_compile for touched Python files\nTested: g0034 sglang-glm5-dev-2 PYTHONPATH=python python -m pytest -q test/registered/unit/mem_cache/test_cp_shared_kv_runtime.py -> 77 passed, 5 warnings, 2 subtests passed\nNot-tested: Full ETE traffic with latest commit; CUDA perf impact of index partial-current prefetch under production load
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