Who spoke the line (RealtimeSessionTimelineGroup.LastTurnRole).
The session-row enrichment, or null when the lookup was unavailable.
The signed-in user's id, or null when the caller does not know it.
Label for a user turn when the caller passes no viewer id.
Who said the card's quoted line.
An agent turn is labeled with the agent's name, or "Agent" when the lookup did not supply one. A user turn is labeled "You" on the viewer's own call and with the caller's name on anyone else's. When the session row doesn't say whose call it was, the label is the neutral "Caller", so a shared conversation never labels someone else's call as yours.
fallbackUserNameis used only when the caller passes no viewer id, and so can't tell whose call it was either way.