The single-via route is right for a detour dragged by hand and wrong for
anything that derives its anchors from a line. Pinning a day onto a recorded
track or a signed scenic road means a couple of dozen points, and one request
each re-routes the entire trip once per point, spaced by the routing host's own
rate limit — twenty anchors would spend half a minute drawing routes nobody
asked to see.
replace_legs names the legs to clear rather than taking a flag for the day, and
that is the whole difference: a traveller who bent two legs by hand and then
adopts a scenic road for a third has not asked to lose the two.
The tools follow in the same change, as parity requires. Undoing a detour picks
this up too, where the vias of one leg were deleted one request at a time.
Maurice
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