ValidVideoLayers checks that each layer's quality is in range but lets a
quality repeat. GetQualityForDimension uses the index into the sorted
layer sizes as the quality, so a list such as LOW, LOW, MEDIUM, HIGH maps
the largest size to index 3, which is OFF, and a subscriber asking for
that size receives no video.
Reject an AddTrack whose layer list repeats a quality. Each list (the
request's and each simulcast codec's) is checked on its own, so the same
qualities on the request and a codec are still accepted. With only three
qualities this also bounds a list to three layers.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
