fix: retain voice codec settings now

ref:

test/utils/voice_message_parser_test.dart

@@ -0,0 +1,152 @@
+import 'dart:typed_data';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_sar_app/utils/voice_message_parser.dart';
+
+void main() {
+  group('VoiceEnvelope', () {
+    test('encodes and parses valid envelope', () {
+      final env = VoiceEnvelope(
+        sessionId: 'deadbeef',
+        mode: VoicePacketMode.mode1200,
+        total: 4,
+        durationMs: 3200,
+        senderKey6: 'aabbccddeeff',
+        timestampSec: 1700000000,
+      );
+
+      final text = env.encodeText();
+      expect(VoiceEnvelope.isVoiceEnvelopeText(text), isTrue);
+
+      final parsed = VoiceEnvelope.tryParseText(text);
+      expect(parsed, isNotNull);
+      expect(parsed!.sessionId, equals('deadbeef'));
+      expect(parsed.mode, equals(VoicePacketMode.mode1200));
+      expect(parsed.total, equals(4));
+      expect(parsed.durationMs, equals(3200));
+      expect(parsed.senderKey6, equals('aabbccddeeff'));
+      expect(parsed.version, equals(1));
+    });
+
+    test('rejects invalid envelope payload', () {
+      final text = 'VE1:nothex:1:2:1000:aabbccddeeff:1700000000:1';
+      expect(VoiceEnvelope.tryParseText(text), isNull);
+    });
+  });
+
+  group('VoiceFetchRequest', () {
+    test('encodes and parses valid request', () {
+      final req = VoiceFetchRequest(
+        sessionId: '00112233',
+        requesterKey6: 'ffeeddccbbaa',
+        timestampSec: 1700000001,
+      );
+      final text = req.encodeText();
+      expect(VoiceFetchRequest.isVoiceFetchRequestText(text), isTrue);
+
+      final parsed = VoiceFetchRequest.tryParseText(text);
+      expect(parsed, isNotNull);
+      expect(parsed!.sessionId, equals('00112233'));
+      expect(parsed.want, equals('all'));
+      expect(parsed.requesterKey6, equals('ffeeddccbbaa'));
+      expect(parsed.version, equals(1));
+    });
+
+    test('rejects invalid request payload', () {
+      expect(
+        VoiceFetchRequest.tryParseText(
+          'VR1:00112233:chunk:ffeeddccbbaa:1700000001:1',
+        ),
+        isNull,
+      );
+    });
+  });
+
+  group('VoicePacket backward compatibility', () {
+    test('parses legacy V: text format', () {
+      final pkt = VoicePacket(
+        sessionId: 'a1b2c3d4',
+        mode: VoicePacketMode.mode700c,
+        index: 0,
+        total: 1,
+        codec2Data: Uint8List.fromList([1, 2, 3, 4]),
+      );
+      final encoded = pkt.encodeText();
+      final parsed = VoicePacket.tryParseText(encoded);
+      expect(parsed, isNotNull);
+      expect(parsed!.sessionId, equals('a1b2c3d4'));
+      expect(parsed.total, equals(1));
+      expect(parsed.codec2Data, equals(Uint8List.fromList([1, 2, 3, 4])));
+    });
+
+    test('constructs binary datagram from actual packet data', () {
+      final actualCodec2 = Uint8List.fromList([
+        0xD3,
+        0x19,
+        0x7A,
+        0x00,
+        0xFE,
+        0x44,
+        0xC1,
+        0x2B,
+        0x88,
+      ]);
+
+      final pkt = VoicePacket(
+        sessionId: '01020304',
+        mode: VoicePacketMode.mode1300,
+        index: 2,
+        total: 5,
+        codec2Data: actualCodec2,
+      );
+
+      final datagram = pkt.encodeBinary();
+      expect(datagram[0], equals(0x56)); // magic 'V'
+      expect(datagram.sublist(1, 5), equals(Uint8List.fromList([1, 2, 3, 4])));
+      expect(datagram[5], equals(VoicePacketMode.mode1300.id));
+      expect(datagram[6], equals(2));
+      expect(datagram[7], equals(5));
+      expect(datagram.sublist(8), equals(actualCodec2));
+
+      final parsed = VoicePacket.tryParseBinary(datagram);
+      expect(parsed, isNotNull);
+      expect(parsed!.sessionId, equals('01020304'));
+      expect(parsed.mode, equals(VoicePacketMode.mode1300));
+      expect(parsed.index, equals(2));
+      expect(parsed.total, equals(5));
+      expect(parsed.codec2Data, equals(actualCodec2));
+    });
+  });
+
+  group('VoiceWaveform', () {
+    test('builds bars from packet bytes', () {
+      final packet = VoicePacket(
+        sessionId: '1234abcd',
+        mode: VoicePacketMode.mode1200,
+        index: 0,
+        total: 1,
+        codec2Data: Uint8List.fromList([
+          0,
+          255,
+          10,
+          245,
+          120,
+          130,
+          64,
+          192,
+          32,
+          224,
+        ]),
+      );
+
+      final bars = VoiceWaveform.buildBarsFromPackets([packet], bars: 8);
+      expect(bars.length, equals(8));
+      expect(bars.every((v) => v >= 0.0 && v <= 1.0), isTrue);
+      expect(bars.any((v) => v > 0.2), isTrue);
+    });
+
+    test('returns zeros for missing packet data', () {
+      final bars = VoiceWaveform.buildBarsFromPackets(const [], bars: 6);
+      expect(bars, equals(List<double>.filled(6, 0.0)));
+    });
+  });
+}