fix: stabilize desktop audio playback

src/native_core/bus.rs

@@ -23,6 +23,7 @@ pub struct NativeBus {
     odd_frame: bool,
     in_vblank: bool,
     frame_complete: bool,
+    cpu_cycles_since_poll: u32,
     mmc3_a12_prev_high: bool,
     mmc3_a12_low_dots: u16,
     mmc3_last_irq_scanline: u32,
@@ -47,6 +48,7 @@ impl NativeBus {
             odd_frame: false,
             in_vblank: false,
             frame_complete: false,
+            cpu_cycles_since_poll: 0,
             mmc3_a12_prev_high: false,
             mmc3_a12_low_dots: 8,
             mmc3_last_irq_scanline: u32::MAX,
@@ -84,6 +86,12 @@ impl NativeBus {
     pub fn clock_cpu(&mut self, cycles: u8) {
         self.clock_cpu_cycles(cycles as u32);
     }
+
+    pub fn take_cpu_cycles_since_poll(&mut self) -> u32 {
+        let cycles = self.cpu_cycles_since_poll;
+        self.cpu_cycles_since_poll = 0;
+        cycles
+    }
 }
 
 // CpuBus trait implementation (memory map + side effects).

src/native_core/bus/tests/apu.rs

@@ -312,3 +312,23 @@ fn dmc_playback_updates_output_level_from_sample_bits() {
 
     assert!(bus.apu.dmc_output_level < initial);
 }
+
+#[test]
+fn pulse_channel_outputs_become_audible_after_setup() {
+    let mut bus = NativeBus::new(Box::new(StubMapper));
+    bus.write(0x4015, 0x01); // enable pulse1
+    bus.write(0x4000, 0b0101_1111); // 25% duty, constant volume=15
+    bus.write(0x4002, 0x08); // low timer period, not sweep-muted
+    bus.write(0x4003, 0x00); // reload length + reset duty sequencer
+
+    let mut saw_non_zero = false;
+    for _ in 0..64u32 {
+        bus.clock_cpu(1);
+        if bus.apu_channel_outputs().pulse1 > 0 {
+            saw_non_zero = true;
+            break;
+        }
+    }
+
+    assert!(saw_non_zero, "pulse1 never produced audible output");
+}

src/native_core/bus/timing.rs

@@ -7,6 +7,7 @@ use crate::native_core::mapper::Mapper;
 
 impl NativeBus {
     fn clock_one_cpu_cycle(&mut self) {
+        self.cpu_cycles_since_poll = self.cpu_cycles_since_poll.saturating_add(1);
         for _ in 0..3 {
             self.clock_ppu_dot();
         }