Verify change-driven maintenance keeps the equivalence index equal to a
from-scratch rebuild under add / edit / remove: an edit into a new bucket
retracts the stale edge, an edit into equivalence adds one, and removing a
connector node propagates a retraction that splits a chorus. Equality checked
against a fresh build() oracle on every operation.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
