1817 composes the whole colorblind pure-sx async stack: the M:1
scheduler, suspending go/wait async, and deterministic virtual-time
sleep/now_ms, over the naked swap_context on guarded mmap stacks. A
coordinator launches three async tasks (sleep 30/10/20 -> return
100/20/3), awaits all three in spawn order, and sums them; tasks
complete in DEADLINE order (task 2@10, 3@20, 1@30), sum 123, final
virtual clock 30 -- fully deterministic.
Stream B1 (fibers + Io + M:1 scheduler) is feature-complete: examples
1800-1817, suite 755/0. Checkpoint + plan marked COMPLETE; next carve
is Stream B2 (channels / cancel / async stdlib).
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