fix(audio): check capture ring available before read (fixes Opus6k choppy)

Partial reads from the capture ring consumed samples that were then
discarded when the send loop retried from buf[0]. For 20ms codecs this
was invisible (single Oboe burst fills 960 samples in one read), but
40ms codecs (Opus6k, 1920 samples) needed 2 bursts — the first partial
read consumed 960 real samples and threw them away.

Result: Opus6k produced ~11 frames/s instead of 25 (~44% of expected).

Fix: expose wzp_native_audio_capture_available() and check it before
reading, matching the desktop capture_ring.available() pattern. Partial
reads no longer occur because we only read when enough samples exist.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-native/src/lib.rs

@@ -264,6 +264,12 @@ pub extern "C" fn wzp_native_audio_stop() {
     }
 }
 
+/// Number of capture samples available to read without blocking.
+#[unsafe(no_mangle)]
+pub extern "C" fn wzp_native_audio_capture_available() -> usize {
+    backend().capture.available_read()
+}
+
 /// Read captured PCM samples from the capture ring. Returns the number
 /// of `i16` samples actually copied into `out` (may be less than
 /// `out_len` if the ring is empty).

desktop/src-tauri/src/engine.rs

@@ -570,16 +570,21 @@ impl CallEngine {
                 if !send_r.load(Ordering::Relaxed) {
                     break;
                 }
-                // wzp-native doesn't expose `available()`, so we just try
+                // Check ring has enough samples before reading to avoid
-                // to read a full frame and sleep briefly if the ring is
+                // partial reads that consume samples and then get
-                // short. Oboe's capture callback fills at a steady rate
+                // overwritten on the next attempt (caused 40ms codecs
-                // so in steady state this spins once per frame.
+                // like Opus6k to produce ~11 frames/s instead of 25).
-                let read = crate::wzp_native::audio_read_capture(&mut buf[..frame_samples]);
+                if crate::wzp_native::audio_capture_available() < frame_samples {
-                if read < frame_samples {
                     short_reads += 1;
                     tokio::time::sleep(std::time::Duration::from_millis(5)).await;
                     continue;
                 }
+                let read = crate::wzp_native::audio_read_capture(&mut buf[..frame_samples]);
+                if read < frame_samples {
+                    // Shouldn't happen after available() check, but guard anyway.
+                    short_reads += 1;
+                    continue;
+                }
                 if !first_full_read_logged {
                     info!(
                         t_ms = send_t0.elapsed().as_millis(),

desktop/src-tauri/src/wzp_native.rs

@@ -28,6 +28,7 @@ static HELLO: OnceLock<unsafe extern "C" fn(*mut u8, usize) -> usize> = OnceLock
 static AUDIO_START: OnceLock<unsafe extern "C" fn() -> i32> = OnceLock::new();
 static AUDIO_START_BT: OnceLock<unsafe extern "C" fn() -> i32> = OnceLock::new();
 static AUDIO_STOP: OnceLock<unsafe extern "C" fn()> = OnceLock::new();
+static AUDIO_CAPTURE_AVAILABLE: OnceLock<extern "C" fn() -> usize> = OnceLock::new();
 static AUDIO_READ_CAPTURE: OnceLock<unsafe extern "C" fn(*mut i16, usize) -> usize> = OnceLock::new();
 static AUDIO_WRITE_PLAYOUT: OnceLock<unsafe extern "C" fn(*const i16, usize) -> usize> = OnceLock::new();
 static AUDIO_IS_RUNNING: OnceLock<unsafe extern "C" fn() -> i32> = OnceLock::new();
@@ -68,6 +69,7 @@ pub fn init() -> Result<(), String> {
         resolve!(AUDIO_START, unsafe extern "C" fn() -> i32, b"wzp_native_audio_start");
         resolve!(AUDIO_START_BT, unsafe extern "C" fn() -> i32, b"wzp_native_audio_start_bt");
         resolve!(AUDIO_STOP, unsafe extern "C" fn(), b"wzp_native_audio_stop");
+        resolve!(AUDIO_CAPTURE_AVAILABLE, extern "C" fn() -> usize, b"wzp_native_audio_capture_available");
         resolve!(AUDIO_READ_CAPTURE, unsafe extern "C" fn(*mut i16, usize) -> usize, b"wzp_native_audio_read_capture");
         resolve!(AUDIO_WRITE_PLAYOUT, unsafe extern "C" fn(*const i16, usize) -> usize, b"wzp_native_audio_write_playout");
         resolve!(AUDIO_IS_RUNNING, unsafe extern "C" fn() -> i32, b"wzp_native_audio_is_running");
@@ -121,6 +123,12 @@ pub fn audio_stop() {
     }
 }
 
+/// Number of capture samples available to read without blocking.
+pub fn audio_capture_available() -> usize {
+    let Some(f) = AUDIO_CAPTURE_AVAILABLE.get() else { return 0; };
+    f()
+}
+
 /// Read captured i16 PCM into `out`. Returns bytes actually copied.
 pub fn audio_read_capture(out: &mut [i16]) -> usize {
     let Some(f) = AUDIO_READ_CAPTURE.get() else { return 0; };