Function reverse_rollback_entry 

pub fn reverse_rollback_entry(
    conn: &Connection,
    entry: &RollbackEntry,
) -> Result<bool>

Reverse a single rollback-log entry. Returns true if a reverse action was applied, false if the entry was already superseded (idempotent rollback).

Collision safety (#300 item 2): before re-inserting a snapshot we check whether another memory now owns the same (title, namespace) key. If it does, we refuse to overwrite — db::insert is an UPSERT on that key and would silently replace the unrelated memory’s content. We return an error so the operator can resolve the conflict manually (delete the offender or rename one of them) rather than clobbering user data.