fix(playback): harden idle queue and gapless transitions

cx

crates/qbz-qt/qml/miniplayer/MiniFooter.qml

@@ -70,6 +70,7 @@ Rectangle {
     readonly property int timeFont: root.compactMode ? 10 : 11
 
     readonly property bool hasTrack: QbzPlayer.npHasTrack
+    readonly property bool canPlay: root.hasTrack || QbzQueue.hasPlayTarget
 
     // --- The pending-seek machine (:214-249) -------------------------------
     // All three constants are load-bearing: the -1.0 SENTINEL (every test is
@@ -273,6 +274,7 @@ Rectangle {
                         icSkip: root.icSkip
                         icPlay: root.icPlay
                         btnEnabled: root.hasTrack
+                        playEnabled: root.canPlay
                     }
 
                     // The capsule (:322-327): right-aligned, vertically centred
@@ -394,6 +396,7 @@ Rectangle {
                         icSkip: 9
                         icPlay: 9
                         btnEnabled: root.hasTrack
+                        playEnabled: root.canPlay
                     }
                 }
 

crates/qbz-qt/qml/miniplayer/MiniTransport.qml

@@ -28,6 +28,9 @@ Row {
     property int gap: 18
     /// Gated on `NowPlayingState.has-track` by the footer (:315).
     property bool btnEnabled: true
+    /// Play additionally accepts an idle, populated queue. The other four
+    /// controls remain tied to a real current track.
+    property bool playEnabled: root.btnEnabled
 
     spacing: root.gap
 
@@ -50,7 +53,7 @@ Row {
         name: QbzPlayer.npPlaying ? "pause" : "play-fill"
         iconSize: root.icPlay
         btn: root.btn
-        btnEnabled: root.btnEnabled
+        btnEnabled: root.playEnabled
         onClicked: QbzPlayer.togglePlay()
     }
     TBtn {

crates/qbz-qt/qml/shell/KioskShell.qml

@@ -577,7 +577,7 @@ Rectangle {
                 // (kiosk_nav_qt.rs:222-225).
                 if (QbzKioskNav.zone === "player") {
                     QbzKioskNav.markActive()
-                    if (QbzPlayer.npHasTrack)
+                    if (QbzPlayer.npHasTrack || QbzQueue.hasPlayTarget)
                         QbzPlayer.togglePlay()
                 } else if (QbzKioskNav.zone === "rail") {
                     QbzKioskNav.markActive()

crates/qbz-qt/qml/shell/TransportControls.qml

@@ -73,6 +73,10 @@ Row {
     // play. Not gated on `npHasTrack`: the first play of a session has no
     // track yet, and that is exactly the case that felt dead.
     readonly property bool loading: QbzPlayer.npLoading
+    // Clear-while-paused removes the NPB cursor by design. Rows added
+    // afterwards still make Play actionable: the backend promotes the first
+    // one without resurrecting the cleared paused stream.
+    readonly property bool playEnabled: QbzPlayer.npHasTrack || QbzQueue.hasPlayTarget
     // Spin phase, advanced on the shared shell pulse (QbzShell.pulseMs).
     property real spinPhase: 0
     Connections {
@@ -94,10 +98,10 @@ Row {
         height: tc.playCircle ? 38 : 34
         radius: tc.playCircle ? width / 2 : theme.radiusSm
         anchors.verticalCenter: parent.verticalCenter
-        opacity: QbzPlayer.npHasTrack ? 1.0 : 0.3
+        opacity: tc.playEnabled ? 1.0 : 0.3
         color: tc.playCircle
-            ? (playArea.containsMouse && QbzPlayer.npHasTrack ? theme.accentHover : theme.accent)
-            : ((playArea.containsMouse && QbzPlayer.npHasTrack) ? theme.surfaceHover : "transparent")
+            ? (playArea.containsMouse && tc.playEnabled ? theme.accentHover : theme.accent)
+            : ((playArea.containsMouse && tc.playEnabled) ? theme.surfaceHover : "transparent")
         QbzIcon {
             // Hidden while loading — the ring below stands in for it, so the
             // button never shows a play glyph for a track that is still being
@@ -145,8 +149,8 @@ Row {
             id: playArea
             anchors.fill: parent
             hoverEnabled: true
-            cursorShape: QbzPlayer.npHasTrack ? Qt.PointingHandCursor : Qt.ArrowCursor
-            onClicked: if (QbzPlayer.npHasTrack) QbzPlayer.togglePlay()
+            cursorShape: tc.playEnabled ? Qt.PointingHandCursor : Qt.ArrowCursor
+            onClicked: if (tc.playEnabled) QbzPlayer.togglePlay()
         }
     }
     QbzIconButton {