Every source in the album and artist chains repeated the same five
lines: stamp the accumulated external failure onto a hit, or OR the
local fault into the running total on a miss. Each new source was a
chance to forget the OR, which is how the local-I/O-settles-absent bug
happened.
chainState.try does both, so each case drops to three lines and the
omission is no longer expressible. Semantics are unchanged: a hit still
carries extErr only. Also drops localErr from resolvePlaylist, which
declared it but never assigned it.
7efb4d1468