> BTW, can I multiplex a single source into
> multiple destinations with fcopy (as tee(1)
> would do)? Should I be able to?

Not "out of the box", because async fcopy is a simple-minded "byte noria", that essentially spends its life alternating a readable and a writable fileevent (in C), guaranteeing no accumulation in memory. The noria requires to be alone fiddling with fileevents in that direction, otherwise there would be a race on the read side.

If instead you want to "fork the flow", simply do a single fcopy towards a synthetic channel (refchan) that duplicates.