fix: separate Cast launch readiness, preserve volume intent and reuse seek inputs

Sources/App/TerebiApp.swift

@@ -1469,7 +1469,7 @@ private struct PlaybackSlider: NSViewRepresentable {
         context.coordinator.parent = self
         slider.minValue = range.lowerBound
         slider.maxValue = range.upperBound
-        slider.doubleValue = value
+        slider.setModelValue(value)
         slider.isEnabled = enabled
         slider.editingChanged = onEditingChanged
         if let cell = slider.cell as? Cell, cell.bufferedRange != bufferedRange {
@@ -1493,6 +1493,21 @@ private struct PlaybackSlider: NSViewRepresentable {
     final class Slider: NSSlider {
         var editingChanged: (Bool) -> Void = { _ in }
         private(set) var tracking = false
+        func setModelValue(_ value: Double) { if !tracking { doubleValue = value } }
+        #if PLAYER_CHECK
+        static func feedbackCheck() -> Bool {
+            let slider = Slider()
+            slider.minValue = 0
+            slider.maxValue = 1
+            slider.doubleValue = 0.8
+            slider.tracking = true
+            slider.setModelValue(0.79)
+            let heldUserValue = slider.doubleValue == 0.8
+            slider.tracking = false
+            slider.setModelValue(0.79)
+            return heldUserValue && slider.doubleValue == 0.79
+        }
+        #endif
         override func mouseDown(with event: NSEvent) {
             guard isEnabled else { return }
             tracking = true
@@ -1538,6 +1553,11 @@ private struct PlaybackSlider: NSViewRepresentable {
     }
 }
 
+#if PLAYER_CHECK
+@MainActor
+func castVolumeSliderFeedbackCheck() -> Bool { PlaybackSlider.Slider.feedbackCheck() }
+#endif
+
 @MainActor
 private struct VideoSurface: NSViewRepresentable {
     let view: NSView