commit
fun commitDisplayPhases(phaseA: String, phaseB: String, displayMeld: Float, playbackReady: Boolean, holdPhase: String?)
Commits the resolved display state for this layer's current frame: stores phaseA/phaseB/ displayMeld as the new phaseAString/phaseBString/meld (and lastMeld), updates viewportPlaybackReady, and records the currently visible phase into viewportHoldPhase (or holdPhase when not playback-ready) so a subsequent frame can retain it if the next target isn't ready.