Cache-hit GSM8K regressions only appeared after the second pass reused request-specific suffix pages, so this change adds fail-fast transfer validation, masks stale rectangular page-table tails, and extends CUDA/unit coverage across FP8 CP shared-KV write, load, top-k, and materialization paths. The temporary ledger records eliminated hypotheses to prevent re-debugging the same L2 and persistent-cache paths.\n\nConstraint: CP shared KV stores physical pages but scheduler-visible semantics must remain valid-token/page-bounded.\nConstraint: bs>1 FP8 prefill must preserve existing CP shared-KV fast paths without silent fallback.\nRejected: Blame raw HiCache L2 load without tests | L2 KV and index backup/load/materialize roundtrips pass on remote CUDA.\nRejected: Disable current/partial reuse broadly | hides the cache-hit contract regression and costs performance.\nConfidence: medium\nScope-risk: moderate\nDirective: Do not weaken CP shared-KV fail-fast or rectangular-tail masking without rerunning second-pass cache-hit accuracy tests.\nTested: remote CUDA pytest for fused FP8 MLA store, fused persistent index store, L2-loaded FP8 KV materialize, L2-loaded index materialize, ragged top-k offset, TAI batched index MQA prepare.\nTested: local py_compile for touched test files and git diff --check.\nNot-tested: full second-pass GSM8K accuracy after these diagnostic tests; root cause remains under investigation.
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