feat(audio): write_wav_mono_16k helper for persisting the mic voiceprint (FR-SPK)

src-tauri/src/audio/mod.rs

@@ -946,6 +946,28 @@ pub fn read_wav_mono_16k(path: &Path) -> Result<Vec<f32>, AudioError> {
     Ok(resampler.process(&mono))
 }
 
+/// Write mono 16kHz `f32` samples as a Float32 WAV — the format
+/// [`read_wav_mono_16k`] reads back. Used to persist the mic voiceprint sample
+/// next to a retained recording so it can be re-matched on reprocess (FR-SPK).
+pub fn write_wav_mono_16k(path: &Path, samples: &[f32]) -> Result<(), AudioError> {
+    let spec = WavSpec {
+        channels: 1,
+        sample_rate: 16_000,
+        bits_per_sample: 32,
+        sample_format: SampleFormat::Float,
+    };
+    let mut writer =
+        WavWriter::create(path, spec).map_err(|e| AudioError::Capture(format!("write wav: {e}")))?;
+    for &s in samples {
+        writer
+            .write_sample(s)
+            .map_err(|e| AudioError::Capture(format!("write wav: {e}")))?;
+    }
+    writer
+        .finalize()
+        .map_err(|e| AudioError::Capture(format!("write wav: {e}")))
+}
+
 /// Ceiling on how far the still-flowing stream may run ahead of a stalled
 /// partner before the mixer forwards it alone — so a muted/dead microphone (or a
 /// silent system output) can't hold up the live transcript. 0.5s @ 16kHz.