process_batch_result_disagg_prefill did one synchronous
hidden_states[i].cpu().clone() per finished request, and stored
topk_p/topk_index as GPU row views whose D2H then happened one by one
inside MetadataBuffers.set_buf — 3*bs device syncs per finished batch
on the scheduler thread. Gather the finishing rows once and do one
D2H per tensor (3 total); requests hold CPU row views, which set_buf
copies CPU-to-CPU into the metadata buffers.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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