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app_sso_service_account is a marker group: membership hides an account from the Users page's People tab entirely (users.ejs filters it out), which is exactly right for a non-person account but has no guardrail against adding a real person by mistake -- which just happened in production (see #113) and looked exactly like the account had vanished. Adding a member to any other group via this dropdown is unchanged (fires immediately, no confirmation); only app_sso_service_account now asks first, via app.messages.confirm. Verified live against a local stack: confirmation shows the right warning, Cancel leaves the group untouched, Confirm adds the member normally, and every other group's add-member flow is unaffected. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>