If user is at the bottom (last message visible
within ~1 bubble height): auto-scroll to show new messages, update
selected to the newest message
If user is scrolled up: do NOT auto-scroll. Show a
visual indicator (e.g., a small blue pill at the bottom of the message
area: “↓ 3 new”). Update selected only if the user was on
the last message before the arrival.
The “New messages” indicator must be dismissable by pressing a
button (e.g., B or Select)
Jump-to-bottom action: a button press (e.g., R1 or Select) scrolls
to the newest message and clears the indicator