fix: resolve fast speech truncation by flushing hardware PCM buffer and extending finalize timeout to 4.5s

src/AppDelegate.swift

@@ -81,8 +81,8 @@ public final class AppDelegate: NSObject, NSApplicationDelegate {
                         }
                     }
                     self.pendingStopWorkItem = workItem
-                    // Trailing grace period: 1.0s (1000ms) buffer so trailing words/syllables right up to key release are never clipped
-                    DispatchQueue.main.asyncAfter(deadline: .now() + 1.00, execute: workItem)
+                    // Trailing grace period: 0.35s (350ms) buffer after key release so trailing fast speech is never clipped
+                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.35, execute: workItem)
                 }
             }
         }
@@ -338,7 +338,7 @@ public final class AppDelegate: NSObject, NSApplicationDelegate {
         
         // Dynamic safety timeout watchdog: scale with audio length & network transit
         let durationSec = Double(pcmData.count) / 32000.0
-        let finalizeTimeout = max(2.5, min(8.0, durationSec * 0.2 + 2.5))
+        let finalizeTimeout = max(4.0, min(12.0, durationSec * 0.25 + 3.5))
         
         let watchdog = DispatchWorkItem { [weak self] in
             guard let self = self, self.isBusyFinalizing else { return }

src/AudioRecorder.swift

@@ -217,14 +217,23 @@ public final class AudioRecorder: NSObject, AVCaptureAudioDataOutputSampleBuffer
     
     public func stopRecording() -> Data {
         lock.lock()
-        defer { lock.unlock() }
+        if !isRecording {
+            let data = pcmBuffer
+            lock.unlock()
+            return data
+        }
+        lock.unlock()
         
-        if !isRecording { return pcmBuffer }
-        isRecording = false
+        // Allow in-flight audio sample buffers on captureQueue to finish processing
+        usleep(60000)
         
-        // Immediately stop hardware capture so macOS orange mic indicator turns OFF
+        lock.lock()
+        isRecording = false
         captureSession?.stopRunning()
-        print("AudioRecorder: Stopped. Microphone hardware OFF. Total PCM captured: \(pcmBuffer.count) bytes.")
-        return pcmBuffer
+        let data = pcmBuffer
+        lock.unlock()
+        
+        print("AudioRecorder: Stopped. Microphone hardware OFF. Total PCM captured: \(data.count) bytes.")
+        return data
     }
 }

src/SonioxClient.swift

@@ -174,8 +174,9 @@ public final class SonioxLiveSession {
         lock.unlock()
         
         print("SonioxLiveSession: Sending finalize packet...")
-        // 1. Send trailing 120ms silence frame so acoustic model cleanly resolves trailing syllables
-        let silenceChunk = Data(count: 3840)
+        // 1. Send trailing 300ms (9600 bytes at 16kHz 16-bit PCM) silence frame
+        // so acoustic CTC model cleanly flushes and resolves trailing fast speech syllables
+        let silenceChunk = Data(count: 9600)
         let silenceMsg = URLSessionWebSocketTask.Message.data(silenceChunk)
         task.send(silenceMsg) { _ in }
         
@@ -191,14 +192,14 @@ public final class SonioxLiveSession {
             }
         }
         
-        // Fast safety timeout fallback: finalize must complete within 1.0s
-        DispatchQueue.global().asyncAfter(deadline: .now() + 1.0) { [weak self] in
+        // Safety timeout fallback: allow up to 4.5s for STT inference & network transit
+        DispatchQueue.global().asyncAfter(deadline: .now() + 4.5) { [weak self] in
             guard let self = self else { return }
             self.lock.lock()
             let stillOpen = !self.isClosed
             self.lock.unlock()
             if stillOpen {
-                print("SonioxLiveSession: Finalize timeout (1.0s) reached — completing.")
+                print("SonioxLiveSession: Finalize timeout (4.5s) reached — completing.")
                 self.completeWithCurrentText()
             }
         }