fix(app): gate on-device transcription hallucinations

app/ios/Runner/AppDelegate.swift

@@ -686,6 +686,8 @@ class SpeechRecognitionHandler: NSObject {
             let request = SFSpeechURLRecognitionRequest(url: fileUrl)
             request.shouldReportPartialResults = false
             request.requiresOnDeviceRecognition = true // Force on-device
+            request.taskHint = .dictation
+            request.addsPunctuation = true
 
             let task = recognizer.recognitionTask(with: request) { (recognitionResult, error) in
                 if let error = error {

app/lib/services/sockets/on_device_apple_provider.dart

@@ -1,17 +1,19 @@
 import 'dart:io';
 import 'dart:typed_data';
 
-import 'package:flutter/services.dart';
+import 'package:flutter/services.dart' show MethodChannel;
 
 import 'package:path_provider/path_provider.dart';
 
 import 'package:omi/models/stt_result.dart';
 import 'package:omi/services/custom_stt_log_service.dart';
+import 'package:omi/services/sockets/on_device_transcript_quality_gate.dart';
 import 'package:omi/services/sockets/pure_polling.dart';
 
 class OnDeviceAppleProvider implements ISttProvider {
   final String language;
   static const MethodChannel _channel = MethodChannel('com.omi.ios/speech');
+  final OnDeviceTranscriptQualityGate _qualityGate = OnDeviceTranscriptQualityGate();
 
   OnDeviceAppleProvider({this.language = 'en'});
 
@@ -45,16 +47,26 @@ class OnDeviceAppleProvider implements ISttProvider {
 
         // Calculate duration: 16kHz * 2 bytes/sample * 1 channel = 32000 bytes/sec
         final duration = audioData.lengthInBytes / 32000.0;
+        final filteredText = _qualityGate.filter(
+          result,
+          audioData: audioData,
+          duration: Duration(microseconds: (duration * Duration.microsecondsPerSecond).round()),
+        );
+        if (filteredText == null) {
+          CustomSttLogService.instance.warning('OnDeviceApple', 'Dropped low-quality local transcript: $result');
+          return null;
+        }
+
         CustomSttLogService.instance.info(
           'OnDeviceApple',
-          'Transcribed ${duration.toStringAsFixed(1)}s in ${sw.elapsedMilliseconds}ms. Text: $result',
+          'Transcribed ${duration.toStringAsFixed(1)}s in ${sw.elapsedMilliseconds}ms. Text: $filteredText',
         );
 
         return SttTranscriptionResult(
           segments: [
-            SttSegment(text: result, start: audioOffsetSeconds, end: audioOffsetSeconds + duration, speakerId: 0),
+            SttSegment(text: filteredText, start: audioOffsetSeconds, end: audioOffsetSeconds + duration, speakerId: 0),
           ],
-          rawText: result,
+          rawText: filteredText,
         );
       } finally {
         if (await tempFile.exists()) {

app/lib/services/sockets/on_device_transcript_quality_gate.dart

@@ -0,0 +1,74 @@
+import 'dart:typed_data';
+
+class OnDeviceTranscriptQualityGate {
+  static const Set<String> _fillerOnlyTokens = {
+    'no',
+    'nope',
+    'nah',
+    'uh',
+    'um',
+    'hmm',
+  };
+  static const int _lowEnergyAverageAbsThreshold = 180;
+
+  String? _lastAcceptedFiller;
+
+  String? filter(String text, {required Uint8List audioData, required Duration duration}) {
+    final cleaned = _clean(text);
+    if (cleaned.isEmpty) return null;
+
+    final normalized = _normalize(cleaned);
+    if (_isFillerOnly(normalized)) {
+      if (_isLowEnergyPcm(audioData)) return null;
+      if (_lastAcceptedFiller == normalized) return null;
+      _lastAcceptedFiller = normalized;
+      return cleaned;
+    }
+
+    _lastAcceptedFiller = null;
+    return cleaned;
+  }
+
+  static String _clean(String text) {
+    return text
+        .replaceAll(RegExp(r'\[.*?\]'), '')
+        .replaceAll(RegExp(r'\(.*?\)'), '')
+        .replaceAll(RegExp(r'\s+'), ' ')
+        .trim();
+  }
+
+  static String _normalize(String text) {
+    return text
+        .toLowerCase()
+        .replaceAll(RegExp(r"[^\p{L}\p{N}\s']+", unicode: true), '')
+        .replaceAll(RegExp(r'\s+'), ' ')
+        .trim();
+  }
+
+  static bool _isFillerOnly(String normalized) => _fillerOnlyTokens.contains(normalized);
+
+  static bool _isLowEnergyPcm(Uint8List bytes) {
+    if (bytes.lengthInBytes < 2) return true;
+    final dataOffset = _wavDataOffset(bytes) ?? 0;
+    if (bytes.lengthInBytes - dataOffset < 2) return true;
+
+    final data = ByteData.sublistView(bytes);
+    var totalAbs = 0;
+    var samples = 0;
+    for (var i = dataOffset; i + 1 < bytes.lengthInBytes; i += 2) {
+      totalAbs += data.getInt16(i, Endian.little).abs();
+      samples += 1;
+    }
+    if (samples == 0) return true;
+    return (totalAbs / samples) < _lowEnergyAverageAbsThreshold;
+  }
+
+  static int? _wavDataOffset(Uint8List bytes) {
+    for (var i = 12; i + 8 <= bytes.lengthInBytes; i += 1) {
+      if (bytes[i] == 0x64 && bytes[i + 1] == 0x61 && bytes[i + 2] == 0x74 && bytes[i + 3] == 0x61) {
+        return i + 8;
+      }
+    }
+    return null;
+  }
+}

app/lib/services/sockets/on_device_whisper_provider.dart

@@ -9,13 +9,15 @@ import 'package:whisper_flutter_new/whisper_flutter_new.dart';
 
 import 'package:omi/models/stt_result.dart';
 import 'package:omi/services/custom_stt_log_service.dart';
+import 'package:omi/services/sockets/on_device_transcript_quality_gate.dart';
 import 'package:omi/services/sockets/pure_polling.dart';
 
 class OnDeviceWhisperProvider implements ISttProvider {
   final String modelPath;
   final String language;
   Whisper? _whisper;
   bool _isInitialized = false;
+  final OnDeviceTranscriptQualityGate _qualityGate = OnDeviceTranscriptQualityGate();
 
   OnDeviceWhisperProvider({required this.modelPath, this.language = 'en'});
 
@@ -31,19 +33,19 @@ class OnDeviceWhisperProvider implements ISttProvider {
 
       WhisperModel targetModel = WhisperModel.tiny;
 
-      if (filename.contains('tiny'))
+      if (filename.contains('tiny')) {
         targetModel = WhisperModel.tiny;
-      else if (filename.contains('base'))
+      } else if (filename.contains('base')) {
         targetModel = WhisperModel.base;
-      else if (filename.contains('small'))
+      } else if (filename.contains('small')) {
         targetModel = WhisperModel.small;
-      else if (filename.contains('medium'))
+      } else if (filename.contains('medium')) {
         targetModel = WhisperModel.medium;
-      else if (filename.contains('large-v1'))
+      } else if (filename.contains('large-v1')) {
         targetModel = WhisperModel.largeV1;
-      else if (filename.contains('large-v2'))
+      } else if (filename.contains('large-v2')) {
         targetModel = WhisperModel.largeV2;
-      else {
+      } else {
         CustomSttLogService.instance.warning(
           'OnDeviceWhisper',
           'Unknown model filename "$filename", defaulting to tiny.',
@@ -86,29 +88,37 @@ class OnDeviceWhisperProvider implements ISttProvider {
 
         final res = await _whisper!.transcribe(transcribeRequest: req);
 
-        if (res.text == null || res.text!.isEmpty) {
+        if (res.text.isEmpty) {
           return null;
         }
 
-        String cleanText = res.text!.trim();
+        String cleanText = res.text.trim();
         cleanText = cleanText.replaceAll(RegExp(r'\[.*?\]'), '').trim();
         cleanText = cleanText.replaceAll(RegExp(r'\(.*?\)'), '').trim();
 
-        if (cleanText.isEmpty) return null;
-
         // Calculate duration: 16kHz * 2 bytes/sample * 1 channel = 32000 bytes/sec
         final duration = audioData.lengthInBytes / 32000.0;
+        final filteredText = _qualityGate.filter(
+          cleanText,
+          audioData: audioData,
+          duration: Duration(microseconds: (duration * Duration.microsecondsPerSecond).round()),
+        );
+        if (filteredText == null) {
+          CustomSttLogService.instance.warning('OnDeviceWhisper', 'Dropped low-quality local transcript: $cleanText');
+          return null;
+        }
+
         final speedFactor = sw.elapsedMilliseconds / 1000 / duration;
         CustomSttLogService.instance.info(
           'OnDeviceWhisper',
-          'Transcribed ${duration.toStringAsFixed(1)}s in ${sw.elapsedMilliseconds}ms (${speedFactor.toStringAsFixed(2)}x real-time). Text: $cleanText',
+          'Transcribed ${duration.toStringAsFixed(1)}s in ${sw.elapsedMilliseconds}ms (${speedFactor.toStringAsFixed(2)}x real-time). Text: $filteredText',
         );
 
         return SttTranscriptionResult(
           segments: [
-            SttSegment(text: cleanText, start: audioOffsetSeconds, end: audioOffsetSeconds + duration, speakerId: 0),
+            SttSegment(text: filteredText, start: audioOffsetSeconds, end: audioOffsetSeconds + duration, speakerId: 0),
           ],
-          rawText: cleanText,
+          rawText: filteredText,
         );
       } finally {
         if (await tempFile.exists()) {

app/lib/services/sockets/transcription_service.dart

@@ -429,8 +429,8 @@ class TranscriptSocketServiceFactory {
       if (Platform.isIOS) {
         return PurePollingSocket(
           config: AudioPollingConfig(
-            bufferDuration: const Duration(seconds: 5),
-            minBufferSizeBytes: sampleRate * 2,
+            bufferDuration: const Duration(seconds: 3),
+            minBufferSizeBytes: sampleRate * 2 * 2,
             serviceId: config.provider.name,
             transcoder: transcoder,
           ),

app/test/unit/on_device_transcription_upgrade_test.dart

@@ -0,0 +1,115 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:omi/services/sockets/on_device_apple_provider.dart';
+import 'package:omi/services/sockets/on_device_transcript_quality_gate.dart';
+
+void main() {
+  group('OnDeviceTranscriptQualityGate', () {
+    test('drops repeated one-word no hallucinations', () {
+      final gate = OnDeviceTranscriptQualityGate();
+
+      expect(gate.filter('no', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)), 'no');
+      expect(gate.filter('No.', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)), isNull);
+      expect(gate.filter(' no ', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)), isNull);
+    });
+
+    test('drops filler no on low-energy audio', () {
+      final gate = OnDeviceTranscriptQualityGate();
+
+      expect(gate.filter('no', audioData: _silentPcmWav(), duration: const Duration(seconds: 3)), isNull);
+    });
+
+    test('keeps real speech and resets duplicate gate', () {
+      final gate = OnDeviceTranscriptQualityGate();
+
+      expect(gate.filter('no', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)), 'no');
+      expect(gate.filter('no problem, start capture', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)),
+          'no problem, start capture');
+      expect(gate.filter('no', audioData: _loudPcmWav(), duration: const Duration(seconds: 3)), 'no');
+    });
+  });
+
+  test('iOS Apple on-device STT uses a multi-second polling window', () {
+    final source = File('lib/services/sockets/transcription_service.dart').readAsStringSync();
+    final appleBlock = RegExp(
+      r'if \(Platform\.isIOS\) \{(?<block>[\s\S]*?)sttProvider: OnDeviceAppleProvider',
+      multiLine: true,
+    ).firstMatch(source)!.namedGroup('block')!;
+
+    expect(appleBlock, contains('bufferDuration: const Duration(seconds: 3)'));
+    expect(appleBlock, contains('minBufferSizeBytes: sampleRate * 2 * 2'));
+  });
+
+  test('native iOS speech fallback is tuned for dictation', () {
+    final source = File('ios/Runner/AppDelegate.swift').readAsStringSync();
+
+    expect(source, contains('request.taskHint = .dictation'));
+    expect(source, contains('request.addsPunctuation = true'));
+  });
+
+  test('Apple on-device STT drops low-energy filler transcripts', () async {
+    TestWidgetsFlutterBinding.ensureInitialized();
+    final tempDir = await Directory.systemTemp.createTemp('on-device-apple-provider-');
+    const pathProviderChannel = MethodChannel('plugins.flutter.io/path_provider');
+    const speechChannel = MethodChannel('com.omi.ios/speech');
+
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+      pathProviderChannel,
+      (call) async => call.method == 'getTemporaryDirectory' ? tempDir.path : null,
+    );
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+      speechChannel,
+      (call) async => 'no',
+    );
+
+    try {
+      final provider = OnDeviceAppleProvider();
+
+      final result = await provider.transcribe(_silentPcmWav());
+
+      expect(result, isNull);
+    } finally {
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+        pathProviderChannel,
+        null,
+      );
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+        speechChannel,
+        null,
+      );
+      if (await tempDir.exists()) await tempDir.delete(recursive: true);
+    }
+  });
+}
+
+Uint8List _silentPcmWav() => _pcmWav(List<int>.filled(1600, 0));
+
+Uint8List _loudPcmWav() => _pcmWav(List<int>.generate(1600, (i) => i.isEven ? 9000 : -9000));
+
+Uint8List _pcmWav(List<int> samples) {
+  final dataSize = samples.length * 2;
+  final out = BytesBuilder();
+  void ascii(String value) => out.add(value.codeUnits);
+  void u16(int value) => out.add([value & 0xff, (value >> 8) & 0xff]);
+  void u32(int value) => out.add([value & 0xff, (value >> 8) & 0xff, (value >> 16) & 0xff, (value >> 24) & 0xff]);
+  ascii('RIFF');
+  u32(36 + dataSize);
+  ascii('WAVEfmt ');
+  u32(16);
+  u16(1);
+  u16(1);
+  u32(16000);
+  u32(32000);
+  u16(2);
+  u16(16);
+  ascii('data');
+  u32(dataSize);
+  for (final sample in samples) {
+    final value = sample < 0 ? 0x10000 + sample : sample;
+    u16(value);
+  }
+  return out.toBytes();
+}