feat: audio - add concurrent mixing, output switching, and device-aware UI

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

@@ -8,6 +8,7 @@
 #include "Hci.hpp"
 #include "A2dp.hpp"
 #include "IntelFirmware.hpp"
+#include <Drivers/Audio/Mixer.hpp>
 #include <Drivers/USB/Xhci.hpp>
 #include <Drivers/USB/UsbDevice.hpp>
 #include <Fs/Vfs.hpp>
@@ -419,10 +420,14 @@ namespace Drivers::USB::Bluetooth {
     void ServiceEvents() {
         if (!g_initialized) return;
         if (Xhci::InPollContext()) return;   // never nest under PollEvents
-        Xhci::PollEvents();
-        Hci::DrainEvents();
         Hci::ProcessPendingCommands();
-        A2dp::PumpMedia();   // feed queued media to the link (no-op when idle)
+        A2dp::ServiceMedia(); // reap events and feed queued media
+        Drivers::Audio::Mixer::OnBluetoothWritable();
+        int requestedVolume;
+        if (A2dp::ConsumeVolumeRequest(&requestedVolume))
+            Drivers::Audio::Mixer::SetMasterVolume(requestedVolume);
+        if (A2dp::ConsumeRouteChange())
+            Drivers::Audio::Mixer::OnBluetoothStateChanged();
     }
 
     // =========================================================================
@@ -605,6 +610,7 @@ namespace Drivers::USB::Bluetooth {
                                 for (int k = 0; k < 200; k++) asm volatile("pause" ::: "memory");
                             }
                             A2dp::StartSource();
+                            Drivers::Audio::Mixer::OnBluetoothStateChanged();
                         }
                         // Persist any new link key now (process context), even if
                         // the link later dropped, so the disk write never stalls