OAuth token in logins.json does not mean the mail account exists

When verifying a Thunderbird account setup from the filesystem, logins.json and prefs.js update on different schedules. The OAuth refresh token is persisted the instant consent is granted, but mail.server.* and mail.account.* prefs are held in memory and only flushed to prefs.js on shutdown or a periodic save. So grepping prefs.js right after setup gives a false negative. The reliable signal that an IMAP account was actually finalized is the existence of the ImapMail/ directory in the profile. Related: autoconfig fails for .edu domains fronted by Exchange Online, which need outlook.office365.com:993 SSL with OAuth2 entered manually.