An account merge blanket-reassigned all of the secondary's identities to the primary,
so merging two accounts that each had a confirmed email (or telegram/vk) left the
survivor with two identities of one kind — which the profile and the retention dossier
both treat as singular (the profile showed an arbitrary one; a later change-email
journaled only one). The merge now keeps the primary's identity and journals the
secondary's colliding one to retained_identities (reason=merge) before dropping it, so
the survivor has one identity per kind and the absorbed credential still lands in the
legal dossier.
- migration 00008: widen retained_identities.reason CHECK to admit 'merge'
(expand-contract — Up only widens the set, so an image rollback stays DB-safe).
- accountmerge: dedupeIdentities + retainMergedIdentity before the identity reassign.
- inttest TestAccountMergeDedupesEmail; docs ARCHITECTURE §4 + retention.go reason note.
Ilia Denisov