Linking makes the secondary user cease to exist as a subject, and Aesthetic Computer keys by subject — `@handles` is findOne({_id: sub}), and it is not the only place. An identity with history behind it cannot be merged at login time; that needs an AC-side re-key first. Found by looking rather than reasoning: me@jas.life has two unlinked Auth0 users, auth0|63effeeb… on the database connection with 783 logins and email|63ed8722… on the passwordless one with 35, and BOTH already own a @handles row pointing at @jeffrey. The Action as written would have merged them and orphaned the second one's history — on the maintainer's own account, on the first real test. So it declines anything with logins_count > 1. An account already split this way keeps working exactly as it does today: two subjects, one handle. Unifying them is a migration, not a login-time decision. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>