diff --git a/rvsttd/src/main.rs b/rvsttd/src/main.rs
index dbde51f..2c3523d 100644
--- a/rvsttd/src/main.rs
+++ b/rvsttd/src/main.rs
@@ -69,12 +69,112 @@ fn line_text(line: &transcript_line_t) -> String {
         .into_owned()
 }
 
+fn unix_now() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs()
+}
+
+// ─── debug session recorder ──────────────────────────────────────────────
+
+struct DebugRecorder {
+    dir: PathBuf,
+    audio: Vec<f32>,
+    log_lines: Vec<String>,
+}
+
+impl DebugRecorder {
+    fn new(base_dir: &PathBuf) -> Self {
+        let dir = base_dir.join(unix_now().to_string());
+        std::fs::create_dir_all(&dir).ok();
+        Self {
+            dir,
+            audio: Vec::new(),
+            log_lines: Vec::new(),
+        }
+    }
+
+    fn log_event(&mut self, event: &str) {
+        self.log_lines.push(format!("[{}] {}", ts(), event));
+    }
+
+    fn log_segment(&mut self, line: &transcript_line_t, prefix: &str) {
+        let text = line_text(line);
+        let event = format!(
+            "SEGMENT id={} prefix={} is_complete={} start={:.3}s duration={:.3}s text=\"{}\"",
+            line.id, prefix, line.is_complete, line.start_time, line.duration, text
+        );
+        self.log_event(&event);
+    }
+
+    fn add_audio(&mut self, samples: &[f32]) {
+        self.audio.extend_from_slice(samples);
+    }
+
+    fn save(self) {
+        // Write log
+        let log_path = self.dir.join("session.log");
+        match std::fs::File::create(&log_path) {
+            Ok(mut f) => {
+                for line in &self.log_lines {
+                    writeln!(f, "{}", line).ok();
+                }
+            }
+            Err(e) => log(&format!("debug: failed to write log: {}", e)),
+        }
+
+        // Write WAV
+        let wav_path = self.dir.join("audio.wav");
+        match write_wav(&wav_path, &self.audio, SAMPLE_RATE as u32) {
+            Ok(()) => {
+                let secs = self.audio.len() as f64 / SAMPLE_RATE as f64;
+                log(&format!("debug: saved {} ({:.1}s, {} samples)", self.dir.display(), secs, self.audio.len()));
+            }
+            Err(e) => log(&format!("debug: failed to write wav: {}", e)),
+        }
+    }
+}
+
+fn write_wav(path: &PathBuf, samples: &[f32], sample_rate: u32) -> Result<()> {
+    let num_samples = samples.len() as u32;
+    let data_size = num_samples * 4; // f32 = 4 bytes
+    let file_size = 44 + data_size;
+
+    let mut f = std::fs::File::create(path)?;
+    // RIFF header
+    f.write_all(b"RIFF")?;
+    f.write_all(&(file_size - 8).to_le_bytes())?;
+    f.write_all(b"WAVE")?;
+    // fmt chunk
+    f.write_all(b"fmt ")?;
+    f.write_all(&16u32.to_le_bytes())?;       // chunk size
+    f.write_all(&3u16.to_le_bytes())?;         // IEEE float
+    f.write_all(&1u16.to_le_bytes())?;         // mono
+    f.write_all(&sample_rate.to_le_bytes())?;
+    f.write_all(&(sample_rate * 4).to_le_bytes())?; // byte rate
+    f.write_all(&4u16.to_le_bytes())?;         // block align
+    f.write_all(&32u16.to_le_bytes())?;        // bits per sample
+    // data chunk
+    f.write_all(b"data")?;
+    f.write_all(&data_size.to_le_bytes())?;
+
+    // Convert f32 samples to little-endian bytes
+    let mut bytes = Vec::with_capacity(data_size as usize);
+    for &s in samples {
+        bytes.extend_from_slice(&s.to_le_bytes());
+    }
+    f.write_all(&bytes)?;
+    Ok(())
+}
+
 // ─── shared state ─────────────────────────────────────────────────────────
 
 struct Shared {
     writer: Mutex<TcpStream>,
     session_id: u64,
     transcriber_handle: i32,
+    debug_dir: Option<PathBuf>,
 }
 
 impl Shared {
@@ -175,6 +275,15 @@ fn transcriber_loop(
     let handle = shared.transcriber_handle;
     let mut sent_ids: HashSet<u64> = HashSet::new();
 
+    // Debug recorder (if enabled)
+    let mut recorder = shared.debug_dir.as_ref().map(|_| DebugRecorder::new(
+        &shared.debug_dir.as_ref().unwrap().join(shared.session_id.to_string()),
+    ));
+
+    if let Some(ref mut r) = recorder {
+        r.log_event(&format!("session {} started", shared.session_id));
+    }
+
     while !stop_signal.load(Ordering::SeqCst) {
         let chunk = {
             let mut buf = audio_buf.lock().unwrap();
@@ -186,6 +295,10 @@ fn transcriber_loop(
             std::mem::take(&mut *buf)
         };
 
+        if let Some(ref mut r) = recorder {
+            r.add_audio(&chunk);
+        }
+
         unsafe {
             moonshine_transcribe_add_audio_to_stream(
                 handle, stream_handle,
@@ -200,6 +313,10 @@ fn transcriber_loop(
             continue;
         }
 
+        if let Some(ref mut r) = recorder {
+            log_transcript_lines(r, t_ptr);
+        }
+
         send_new_segments(&shared, t_ptr, &mut sent_ids, "P");
     }
 
@@ -207,6 +324,10 @@ fn transcriber_loop(
     if aborted.load(Ordering::SeqCst) {
         unsafe { moonshine_stop_stream(handle, stream_handle) };
         log(&format!("Session {} aborted, skipping final flush", shared.session_id));
+        if let Some(mut r) = recorder {
+            r.log_event("aborted (new session took over)");
+            r.save();
+        }
         return;
     }
 
@@ -215,6 +336,11 @@ fn transcriber_loop(
         let mut buf = audio_buf.lock().unwrap();
         std::mem::take(&mut *buf)
     };
+
+    if let Some(ref mut r) = recorder {
+        r.add_audio(&remaining);
+    }
+
     if !remaining.is_empty() {
         unsafe {
             moonshine_transcribe_add_audio_to_stream(
@@ -234,6 +360,10 @@ fn transcriber_loop(
         let t = unsafe { &*t_ptr };
         let mut new_segments: Vec<String> = Vec::new();
 
+        if let Some(ref mut r) = recorder {
+            log_transcript_lines(r, t_ptr);
+        }
+
         for i in 0..t.line_count as usize {
             let line = unsafe { &*t.lines.add(i) };
             if line.text.is_null() || line.is_complete == 0 {
@@ -255,10 +385,32 @@ fn transcriber_loop(
             for (i, text) in new_segments.iter().enumerate() {
                 let prefix = if i == last { "F" } else { "P" };
                 shared.send_msg(prefix, text);
+                if let Some(ref mut r) = recorder {
+                    r.log_event(&format!("TX {} \"{}\"", prefix, text));
+                }
             }
         }
     } else {
         shared.send_msg("F", "");
+        if let Some(ref mut r) = recorder {
+            r.log_event("TX F (empty)");
+        }
+    }
+
+    if let Some(mut r) = recorder {
+        r.log_event("session ended");
+        r.save();
+    }
+}
+
+fn log_transcript_lines(recorder: &mut DebugRecorder, t_ptr: *const transcript_t) {
+    let t = unsafe { &*t_ptr };
+    for i in 0..t.line_count as usize {
+        let line = unsafe { &*t.lines.add(i) };
+        if line.text.is_null() {
+            continue;
+        }
+        recorder.log_segment(line, if line.is_complete != 0 { "complete" } else { "partial" });
     }
 }
 
@@ -468,17 +620,22 @@ fn main() -> Result<()> {
 
     let mut args = first.into_iter().chain(args);
     let mut model_dir = default_model;
+    let mut debug = false;
 
     while let Some(a) = args.next() {
         match a.as_str() {
             "--model-dir" | "-m" => {
                 model_dir = args.next().unwrap_or(model_dir);
             }
+            "--debug" => {
+                debug = true;
+            }
             "--help" | "-h" => {
-                println!("Usage: rvsttd [--model-dir DIR]");
+                println!("Usage: rvsttd [--model-dir DIR] [--debug]");
                 println!("       rvsttd fetch [DIR]");
                 println!("Listens on TCP {}", BIND_ADDR);
                 println!("Model: medium-streaming (Moonshine)");
+                println!("--debug: save session audio + transcript log to ~/.rvsttd/debug/");
                 println!("'rvsttd fetch' downloads the English medium-streaming model");
                 return Ok(());
             }
@@ -486,6 +643,15 @@ fn main() -> Result<()> {
         }
     }
 
+    let debug_dir = if debug {
+        let d = PathBuf::from(&home).join(".rvsttd").join("debug");
+        std::fs::create_dir_all(&d).ok();
+        log(&format!("Debug mode enabled — sessions saved to {}", d.display()));
+        Some(d)
+    } else {
+        None
+    };
+
     let model_path = std::fs::canonicalize(&model_dir)
         .unwrap_or_else(|_| std::path::PathBuf::from(&model_dir));
 
@@ -547,6 +713,7 @@ fn main() -> Result<()> {
                     writer: Mutex::new(writer_stream.try_clone()?),
                     session_id: new_session_id,
                     transcriber_handle,
+                    debug_dir: debug_dir.clone(),
                 });
 
                 log(&format!("PTT on session {}", new_session_id));