TestAlert called Enqueue, which is the pure test seam: it fills the queue and returns. The
alert layer needs three more things to show anything — its scene list, the playback ticker
running, and the preview refreshed — and all three live in OnMessageReceived, the same entry
the chat feed uses (MainViewModel.Chat.cs).
Now it calls OnMessageReceived(message, Scenes), so the clip advances on the ticker and writes
frames to the box's VideoImageSource, which is what the preview pane displays.
gramps
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