isAccountConnected

Whether accountId specifically has a live, authenticated session right now.

connectionState is protocol-wide: for protocols that support several simultaneous accounts (XMPP, Matrix) it flips to ConnectionState.CONNECTED as soon as any account connects, so it cannot tell "account A is connected" apart from "account B is connected but A isn't". Callers that need to avoid needlessly reconnecting an already-live session (e.g. ltechnologies.onionphone.securemessenger.service.ConnectionManager's account restore, which must not churn a healthy connection just because a sibling account of the same protocol is mid-(re)connect) must check this per-account signal instead. Default implementation falls back to the protocol-wide state for single-account protocols.