Fires once the keyshare has been backed up.
Fires on every change to huddle membership (and once with the initial set
when AccountCeremony.wait starts). Drives an "N of M joined"
presence UI; signers carries the full expected party list (humans +
robos, present or not) for a per-signer view.
Fires once when all required signers are present — the huddle is ready to proceed. Mirrors AccountCeremony.isReady for push-style consumers. Re-arms and fires again if membership drops below quorum and recovers. Late subscribers should read AccountCeremony.isReady.
Fires when the keygen ceremony completes and the public key is derived.