calculate_mla_kv_cache_dim only packs fp8 (override dim -> nsa_kv_cache_store_fp8=True, required by the flashmla_sparse dequant path) when NEITHER prefill nor decode backend is trtllm. The Blackwell-no-DP guard defaulted the unset side to trtllm, producing a mixed flashmla/trtllm pair that left fp8 KV unpacked and crashed flashmla_sparse ('kv must have dtype bf16'). Now an explicit flashmla choice on either side pulls the unset side to flashmla too.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit ed30312c3d599595e40ae99bc2832159b634cca6)
leavelet
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