Adds the listener-side fan-in for the speaker-avatar reaction
overlay (T1 #3):
recentReactions: StateFlow<Map<String, List<RoomReaction>>>
onReactionEvent(event, nowSec, windowSec = 30)
evictReactions(olderThanSec)
The platform layer is the source — amethyst observes LocalCache for
kind=7 with #a=[roomATag] and pipes events here. The 30-s window
constant lives next to SPEAKING_TIMEOUT_MS so the staleness
configuration is one place. Caller-driven tick (no internal timer
inside the VM) keeps the lifecycle aligned with the Composable.
Test:
* onReactionEventGroupsByTargetAndEvictsOnTick — two reactions on
bob arrive within the window; tick advances past the window;
overlay clears.
Claude
aa4c24b974