ui: refine subtitle layout and preserve hidden controls on seeks

Checks/system-playback.swift

@@ -183,6 +183,21 @@ struct SystemPlaybackChecks {
         require(model.setPlayback(playing: true), "repeated play accepted")
         until("repeated play keeps playing") { model.state.status == PLAYER_PLAYING && model.state.position > 0.2 }
 
+        if !NSWorkspace.shared.isVoiceOverEnabled {
+            require(model.perform(.enterCompact), "compact playback is available for hidden-keyboard seeking")
+            until("compact entry completes before hiding controls") { !model.compactWindow.isTransitioning }
+            model.hideControls(hideCursor: false)
+            require(!model.controlsVisible, "playing chrome can be hidden before a keyboard seek")
+            require(model.handleKey(try! KeyChord("left")), "keyboard seek is accepted while chrome is hidden")
+            require(!model.controlsVisible, "keyboard seek must not flash playback chrome")
+            until("hidden keyboard seek acknowledges the start boundary") {
+                require(!model.controlsVisible, "seek acknowledgement must preserve hidden chrome")
+                return !model.state.seek_pending && model.state.position < 0.15
+            }
+            require(model.perform(.exitCompact), "keyboard seek check restores normal mode")
+            until("compact exit completes") { !model.compactWindow.isTransitioning }
+        }
+
         // Closing must hide the last polled retained range before the next state poll.
         var retainedSnapshot = model.state
         retainedSnapshot.buffered_start = retainedSnapshot.position