feat(#430): report chunk count in caplog truncation error

Adds the received CHUNK-frame count to CaplogTruncatedException and the
on-screen error ("received X of Y bytes in N chunks"). This diagnostic
pinpointed the near-full BLE truncation: 94 chunks (all frames arrived) but
each full frame 3 bytes short = BLE MTU clipping 176-byte caplog frames to
173. Firmware chunk-size cap for BLE tracked with TopazHill.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/connector/caplog_reassembler.dart

@@ -77,10 +77,17 @@ class CaplogTruncatedException implements Exception {
   const CaplogTruncatedException({
     required this.received,
     required this.expected,
+    this.chunks,
   });
   final int received;
   final int expected;
+
+  /// Number of CHUNK frames the client accumulated before END — a diagnostic to
+  /// tell client/transport frame loss apart from the firmware streaming short.
+  final int? chunks;
+
   @override
   String toString() =>
-      'CaplogTruncatedException: received $received of $expected bytes';
+      'CaplogTruncatedException: received $received of $expected bytes'
+      '${chunks != null ? ' in $chunks chunks' : ''}';
 }

lib/connector/meshcore_connector.dart

@@ -290,6 +290,7 @@ class MeshCoreConnector extends ChangeNotifier {
   bool _caplogAwaitingStart = false;
   Completer<CaplogAck>? _caplogAckCompleter;
   Completer<CaplogDeviceStatus>? _caplogStatusCompleter;
+  int _caplogChunks = 0; // CHUNK frames in the active download (diagnostic)
   String? _firmwareVersion;
   String? _deviceModel;
   int? _offbandCaps;
@@ -4354,10 +4355,15 @@ class MeshCoreConnector extends ChangeNotifier {
     switch (event.status) {
       case CaplogStatus.started:
         _caplogAwaitingStart = false;
+        _caplogChunks = 0;
+        break;
+      case CaplogStatus.chunk:
+        _caplogChunks++;
         break;
       case CaplogStatus.completed:
         _appDebugLogService?.info(
-          'Caplog download complete: ${event.bytes!.length} bytes',
+          'Caplog download complete: ${event.bytes!.length} bytes in '
+          '$_caplogChunks chunks',
           tag: 'Caplog',
         );
         completer.complete(event.bytes);
@@ -4365,17 +4371,17 @@ class MeshCoreConnector extends ChangeNotifier {
       case CaplogStatus.truncated:
         _appDebugLogService?.warn(
           'Caplog download truncated: ${event.bytes!.length} of '
-          '${event.expected} bytes',
+          '${event.expected} bytes in $_caplogChunks chunks',
           tag: 'Caplog',
         );
         completer.completeError(
           CaplogTruncatedException(
             received: event.bytes!.length,
             expected: event.expected!,
+            chunks: _caplogChunks,
           ),
         );
         break;
-      case CaplogStatus.chunk:
       case CaplogStatus.ignored:
         break;
     }