Scheduler tracks per-producer block_ids (accumulated from scheduler_output)
and emits per-step LWSendMeta with cumulative computed_tokens. Worker
lw_wait_for_save records a CUDA event per step and enqueues progress; the
sender-loop ship loop drains it, shipping only computed+dst-wanted+unshipped
blocks in order (correct under chunked prefill). Per-transfer state =
concurrent-safe. Keeps v1 single-transfer version as reference.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Gahow Wang
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