Optional ReadonlyleadThe leading kind when the template writes it out (/channel/matrix/{index}) rather than
carrying it as {kind}. Then {index} is the only leading variable — and the id does NOT
repeat the kind, because the path already said it. Kind in the path stays kind in the path:
a crosspoint id is { index, srcKind, srcIndex } on the wire, and adding a kind field
would be a second spelling of one instance.
ReadonlyleadsThe end the /channel/… prefix names.
ReadonlytrailReadonlytrailThe trailing end's own wire keys — busKind/busIndex, srcKind/srcIndex.
How one pair-shaped path spells its two ends.
The path's leading
/channel/…segments name one end; the other is two named keys further down the template. Which end leads, and whether the leading kind is written LITERALLY in the template, are the only two things that differ between pair rows.