fix: fix Bluetooth audio delay

kernel/src/Drivers/USB/Bluetooth/A2dp.cpp

@@ -119,7 +119,15 @@ namespace Drivers::USB::Bluetooth::A2dp {
     // PCM ring between WriteAudio (producer, syscall context) and PumpMedia
     // (consumer, idle-loop/syscall context).  Absolute byte counters wrapping
     // mod 2^32: fill = head - tail, buffer index = counter & (SIZE - 1).
-    constexpr uint32_t PCM_RING_SIZE = 128 * 1024;   // ~0.68 s at 48 kHz stereo
+    //
+    // The ring's size IS output latency: the mixer pumps whenever it has
+    // room, so in steady state the ring sits full (silence included, while a
+    // stream is paused) and every pause, seek and volume change is heard only
+    // after it drains.  It was 128 KiB (~0.68 s), which with LEAD_MS and the
+    // sink's own buffer put the headphones ~1 s behind the app.  Stall
+    // tolerance comes from LEAD_MS at the sink plus the mixer's per-stream
+    // rings upstream, so this only needs to bridge the gap between pumps.
+    constexpr uint32_t PCM_RING_SIZE = 16 * 1024;    // ~85 ms at 48 kHz stereo
     constexpr uint64_t LEAD_MS = 150;                // sink jitter-buffer target
     static uint8_t g_pcmRing[PCM_RING_SIZE];
     static std::atomic<uint32_t> g_ringHead{0};      // producer: WriteAudio