diff --git a/crates/oakaudio/src/manager.rs b/crates/oakaudio/src/manager.rs
index 44029fae8..d7512ed88 100644
--- a/crates/oakaudio/src/manager.rs
+++ b/crates/oakaudio/src/manager.rs
@@ -473,16 +473,45 @@ mod tests {
 	use super::*;
 
 	/// M12 P1 acceptance: the PortAudio output callback pulls pushed
-	/// samples and advances the playback clock. Requires real audio
-	/// hardware; skips (returns) when PortAudio is unavailable.
+	/// samples and advances the playback clock. Requires a working audio
+	/// session; skips (returns) when PortAudio cannot deliver callbacks
+	/// (CI boxes, background/headless macOS sessions where CoreAudio
+	/// starts the stream but never runs it).
 	#[test]
 	fn output_callback_consumes_pushed_samples() {
-		// Skip when there is no audio system (CI boxes).
-		let pa = match portaudio::PortAudio::new() {
-			Ok(pa) => pa,
-			Err(_) => return,
-		};
-		if pa.default_output_device().is_err() {
+		// Skip when the audio system cannot actually run a stream: open a
+		// silent stream and require at least one callback within 2 s. A
+		// device existing is not enough — headless sessions report
+		// is_active=true while delivering zero callbacks.
+		use std::sync::atomic::AtomicI64 as A;
+		static PROBE: A = A::new(0);
+		let can_play = (|| {
+			let pa = portaudio::PortAudio::new().ok()?;
+			let dev = pa.default_output_device().ok()?;
+			let info = pa.device_info(dev).ok()?;
+			let params = portaudio::StreamParameters::<f32>::new(
+				dev,
+				2,
+				true,
+				info.default_low_output_latency,
+			);
+			let settings = portaudio::OutputStreamSettings::new(params, 48000.0, 512);
+			let cb = move |args: portaudio::OutputStreamCallbackArgs<f32>| {
+				PROBE.fetch_add(args.frames as i64, Ordering::Relaxed);
+				portaudio::Continue
+			};
+			let mut stream = pa.open_non_blocking_stream(settings, cb).ok()?;
+			stream.start().ok()?;
+			let deadline = std::time::Instant::now() + std::time::Duration::from_secs(2);
+			while std::time::Instant::now() < deadline && PROBE.load(Ordering::Relaxed) == 0 {
+				std::thread::sleep(std::time::Duration::from_millis(50));
+			}
+			let got = PROBE.load(Ordering::Relaxed) > 0;
+			let _ = stream.stop();
+			Some(got)
+		})();
+		if can_play != Some(true) {
+			eprintln!("audio session cannot deliver callbacks; skipping");
 			return;
 		}
 
@@ -516,12 +545,22 @@ mod tests {
 		)
 		.expect("push succeeds even without an explicit device");
 
-		// Give the audio thread time to consume.
-		std::thread::sleep(std::time::Duration::from_millis(300));
-		let consumed = {
-			let m = with_instance(&h).unwrap();
-			m.output_buffer.output_frames_consumed()
-		};
+		// Give the audio thread time to consume. PortAudio/CoreAudio
+		// stream startup can take SECONDS in some environments (audio HAL
+		// device probing), so poll with a generous deadline instead of a
+		// fixed sleep.
+		let deadline = std::time::Instant::now() + std::time::Duration::from_secs(30);
+		let mut consumed = 0i64;
+		while std::time::Instant::now() < deadline {
+			{
+				let m = with_instance(&h).unwrap();
+				consumed = m.output_buffer.output_frames_consumed();
+			}
+			if consumed > 0 {
+				break;
+			}
+			std::thread::sleep(std::time::Duration::from_millis(100));
+		}
 		assert!(
 			consumed > 0,
 			"the output callback must consume pushed frames"
diff --git a/crates/oakaudio/src/outputdevice.rs b/crates/oakaudio/src/outputdevice.rs
index b96e10b47..a91b82f1b 100644
--- a/crates/oakaudio/src/outputdevice.rs
+++ b/crates/oakaudio/src/outputdevice.rs
@@ -116,14 +116,18 @@ impl PortAudioOutput {
 		// The callback pulls whole frames from the shared device and
 		// advances the output clock (underrun → silence). `read` locks
 		// the device internally; no other locks are taken on the audio
-		// thread.
+		// thread. The scratch buffer is allocated once and reused —
+		// allocating per callback would violate the real-time rule.
 		let sink_cb = sink.clone();
+		let scratch = std::cell::RefCell::new(Vec::<u8>::new());
 		let callback = move |args: OutputStreamCallbackArgs<f32>| {
 			let out = args.buffer;
 			let frames = args.frames;
 			let total = frames * channels.max(1) as usize;
-			let mut byte_buf = vec![0u8; total * 4];
-			let got = sink_cb.read(&mut byte_buf);
+			let mut scratch = scratch.borrow_mut();
+			scratch.resize(total * 4, 0);
+			let byte_buf = &mut *scratch;
+			let got = sink_cb.read(byte_buf);
 			let frames_got = (got as usize) / (channels.max(1) as usize * 4);
 			// Convert the interleaved f32 bytes in place to a sample
 			// slice (PortAudio writes f32s directly).
diff --git a/crates/oakaudio/src/waveform.rs b/crates/oakaudio/src/waveform.rs
index f6b85e964..7ec8ce313 100644
--- a/crates/oakaudio/src/waveform.rs
+++ b/crates/oakaudio/src/waveform.rs
@@ -731,12 +731,10 @@ pub fn extract(
 	// Probe for the stream's native rate/layout (stateless).
 	// SAFETY: `filename` is a NUL-terminated C string (validated by the FFI
 	// layer); the probe handle is freed on every path below.
-	eprintln!("DBG-WF: probing");
 	let mut probe = unsafe { crate::bridge::codec::oakcodec_decoder_probe(filename.as_ptr()) };
 	if probe.is_null() {
 		return Err(Error::NotFound);
 	}
-	eprintln!("DBG-WF: probed");
 	let mut info = unsafe { std::mem::zeroed::<AudioStreamInfo>() };
 	let r = unsafe {
 		crate::bridge::codec::oakcodec_decoder_probe_get_audio_stream(
@@ -764,7 +762,6 @@ pub fn extract(
 	// (`retrieve_audio` delivers interleaved f32 at the requested native
 	// rate/layout; the C++ path ran the decode through an identity
 	// fb_audio_graph to obtain planar f32).
-	eprintln!("DBG-WF: opening decoder stream {}", info.stream_index);
 	let decoder = FFmpegDecoder::new();
 	let stream = CodecStream::with_block(
 		filename.to_string_lossy().into_owned(),
@@ -774,7 +771,6 @@ pub fn extract(
 	if let Err(e) = decoder.open(&stream) {
 		return Err(Error::Failed(format!("failed to open decoder: {e:?}")));
 	}
-	eprintln!("DBG-WF: opened");
 
 	if info.time_base_num <= 0 || info.time_base_den <= 0 || info.duration_ts <= 0 {
 		let _ = decoder.close();
@@ -803,7 +799,6 @@ pub fn extract(
 			Rational::new(offset, i64::from(info.sample_rate)),
 			Rational::new(offset + frames, i64::from(info.sample_rate)),
 		);
-		eprintln!("DBG-WF: decoding chunk at {offset}");
 		let mut buf = vec![0f32; frames as usize * channels as usize];
 		match decoder.retrieve_audio(&mut buf, &range, info.sample_rate, layout_mask) {
 			Ok(RetrieveAudioStatus::Success) => {