fix(audio): check real CoreAudio device rate with macOS Shared Mode

crates/qbz-audio/src/backend.rs

@@ -504,8 +504,36 @@ impl AudioBackend for CpalDefaultBackend {
                 .ok_or_else(|| "No default output device found".to_string())?
         };
 
-        let mixer_sink = DeviceSinkBuilder::from_device(device)
-            .map_err(|e| format!("Failed to create device sink builder: {}", e))?
+        #[cfg(target_os = "macos")]
+        let shared_mode_override = if !config.exclusive_mode {
+            Self::shared_mode_nominal_stream_config(
+                &device,
+                effective_device_id.map(|name| name.as_str()),
+            )
+        } else {
+            None
+        };
+
+        let builder = DeviceSinkBuilder::from_device(device)
+            .map_err(|e| format!("Failed to create device sink builder: {}", e))?;
+
+        #[cfg(target_os = "macos")]
+        let mixer_sink = if let Some(override_config) = shared_mode_override {
+            let buffer_size =
+                rodio::cpal::BufferSize::Fixed((override_config.sample_rate() / 20).max(64));
+            builder
+                .with_supported_config(&override_config)
+                .with_buffer_size(buffer_size)
+                .open_stream()
+                .map_err(|e| format!("Failed to create output stream: {}", e))?
+        } else {
+            builder
+                .open_stream()
+                .map_err(|e| format!("Failed to create output stream: {}", e))?
+        };
+
+        #[cfg(not(target_os = "macos"))]
+        let mixer_sink = builder
             .open_stream()
             .map_err(|e| format!("Failed to create output stream: {}", e))?;
 
@@ -561,6 +589,66 @@ impl AudioBackend for CpalDefaultBackend {
 
 #[cfg(target_os = "macos")]
 impl CpalDefaultBackend {
+    /// In macOS shared mode, CPAL's default config can briefly report a stale
+    /// sample rate after CoreAudio changes the device's nominal rate. If we
+    /// trust the stale rate, playback can run at the wrong speed until the
+    /// stream is recreated. Prefer opening the CPAL stream at CoreAudio's
+    /// current nominal rate when the two disagree.
+    fn shared_mode_nominal_stream_config(
+        device: &rodio::cpal::Device,
+        effective_device_name: Option<&str>,
+    ) -> Option<rodio::cpal::SupportedStreamConfig> {
+        use crate::coreaudio_direct;
+
+        let device_id = match effective_device_name {
+            Some(name) => coreaudio_direct::find_device_by_name(name).ok().flatten(),
+            None => coreaudio_direct::get_default_output_device().ok(),
+        }?;
+        let nominal_rate = coreaudio_direct::get_nominal_sample_rate(device_id).ok()?;
+        let default_config = device.default_output_config().ok()?;
+        let default_rate = default_config.sample_rate();
+        if nominal_rate == default_rate {
+            return None;
+        }
+
+        let supported_configs: Vec<_> = device.supported_output_configs().ok()?.collect();
+        let matching_config = supported_configs
+            .iter()
+            .find_map(|range| {
+                if range.channels() == default_config.channels()
+                    && range.sample_format() == default_config.sample_format()
+                {
+                    (*range).try_with_sample_rate(nominal_rate)
+                } else {
+                    None
+                }
+            })
+            .or_else(|| {
+                supported_configs
+                    .iter()
+                    .find_map(|range| (*range).try_with_sample_rate(nominal_rate))
+            });
+
+        let device_label = effective_device_name.unwrap_or("System Default");
+        if matching_config.is_some() {
+            log::warn!(
+                "[CoreAudio] Shared-mode rate mismatch on '{}': CPAL default {}Hz vs CoreAudio nominal {}Hz. Opening stream at the nominal rate to avoid wrong-speed playback.",
+                device_label,
+                default_rate,
+                nominal_rate
+            );
+        } else {
+            log::warn!(
+                "[CoreAudio] Shared-mode rate mismatch on '{}': CPAL default {}Hz vs CoreAudio nominal {}Hz, but no supported CPAL config matched the nominal rate.",
+                device_label,
+                default_rate,
+                nominal_rate
+            );
+        }
+
+        matching_config
+    }
+
     /// Probe a macOS audio device for capabilities via CoreAudio APIs.
     /// Returns (supported_rates, max_rate, bus_type, is_hardware).
     fn probe_macos_device(