feat: audio stack performance improvements

kernel/src/Drivers/Audio/IntelHda.hpp

@@ -274,6 +274,13 @@ namespace Drivers::Audio::IntelHda {
     // Returns number of bytes written (may be less than requested if buffer full).
     int Write(int handle, const uint8_t* data, uint32_t size);
 
+    // Free bytes in the DMA ring that a caller may write right now.
+    // Returns 0 if the stream is not active. The mixer uses this to size
+    // each pump so it never produces more than HDA can accept (otherwise
+    // surplus mixed data would be silently dropped and the stream readers
+    // would still advance, scrambling playback).
+    uint32_t GetWriteSpace(int handle);
+
     // Control commands
     constexpr int AUDIO_CTL_SET_VOLUME = 0;   // value: 0-100
     constexpr int AUDIO_CTL_GET_VOLUME = 1;