Preserve absorbed identities for old references

Context

Bookmarks and integrations still hold record identities after their records are removed.

Decision

Every absorbed identity retains a unique alias to its survivor and merge; record operations report that it was merged, later merges repoint aliases, and database guards prevent identity reuse.

Alternatives Considered

Return the survivor without explaining the move. Clients could associate the survivor’s values with the wrong stored identity.

Return ordinary not-found. Clients could mistake a merge for deletion and recreate the same person.

Consequences

Alias resolution follows a single destination. Ordinary survivor deletion can leave a dangling destination and remains a defect. Reset and purge remove aliases so later reloads can reuse identities.