Order of preference: a providedLabel (e.g. the lesson roster's
display name) → username extracted from an email-like userId →
first 6 chars of the hashed id (fallback for opaque ids). The
fallback never returns the raw userId — it's typically too long
and may leak user data into the overlay.
Returns a human-readable label for the peer.
Order of preference: a
providedLabel(e.g. the lesson roster's display name) → username extracted from an email-like userId → first 6 chars of the hashed id (fallback for opaque ids). The fallback never returns the raw userId — it's typically too long and may leak user data into the overlay.