When the display/system sleeps with a video paused, the window server
stops completing CAMetalLayer presents and mpv's MoltenVK swapchain wedges,
pinning one core at 100% until the app exits. occlusionState does not
reliably change on display sleep, so observe NSWorkspace screensDidSleep/
Wake to hide the metal layer (and drop the playback activity) while dark,
restoring on wake with a forced redraw when paused to avoid a stale frame.
Pairs with MPVKit v1.0.10, which gates libmpv presentation on the layer's
hidden state (check_visible) so presents actually stop while hidden.
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