The marker claimed to be scoped to the parsed set's value and was scoped
to a lossy rendering of it: `tr -c '[:alnum:]' '-'` maps `acme/widgets#9`
and `acme-widgets#9` — both parses this reconciler accepts — onto one
marker, so a declaration edited between them found the old echo and said
nothing. Silence in exactly the case the echo exists to speak about.
The identity is now a digest of the exact rendered set. The readable slug
stays in front of it and decides nothing. Distinguishing `/` would have
closed the reported pair and left the class: `-`, `_` and `.` are all
legal in a qualifier and all collapse the same way, so all four are
pinned, and the sweep probe observes the second echo actually landing.
Refs #252