fix(#154): make PathHelper width-aware (chat + path-management path displays)

PathHelper.formatPathHex / resolvePathNames assumed 1 byte per hop, so the
direct-chat "full path" and path-management dialogs rendered routing paths
per-byte (84,AB instead of 84AB) and resolved hop names by a single byte on
2-/3-byte path-hash meshes. Group bytes into pathHashByteWidth-sized hops and
match hop names by the full-width prefix.

- formatPathHex(bytes, width) / resolvePathNames(bytes, contacts, width) group
  into width-byte hops (trailing partial hop kept); name match uses the full
  hop prefix.
- chat_screen + path_management_dialog pass connector.pathHashByteWidth.

analyze clean; 7 PathHelper tests (incl. width-2 collision-avoidance); Gemini: ship.

Closes #154

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

lib/helpers/path_helper.dart

@@ -2,30 +2,58 @@ import '../models/contact.dart';
 import '../connector/meshcore_protocol.dart';
 
 class PathHelper {
-  static String formatPathHex(List<int> pathBytes) {
-    return pathBytes
-        .map((b) => b.toRadixString(16).padLeft(2, '0').toUpperCase())
-        .join(',');
+  /// Path bytes as comma-separated hops, each hop [hashWidth] bytes of hex. (#154)
+  static String formatPathHex(List<int> pathBytes, int hashWidth) {
+    return _hopGroups(pathBytes, hashWidth).map(_hopHex).join(',');
   }
 
+  /// Resolves each [hashWidth]-byte hop to a repeater/room name, falling back to
+  /// the hop's hex prefix when no contact matches. (#154)
   static String resolvePathNames(
     List<int> pathBytes,
     List<Contact> allContacts,
+    int hashWidth,
   ) {
-    return pathBytes
-        .map((b) {
-          final hex = b.toRadixString(16).padLeft(2, '0').toUpperCase();
+    return _hopGroups(pathBytes, hashWidth)
+        .map((hop) {
           final matches = allContacts
               .where(
                 (c) =>
-                    c.publicKey.first == b &&
+                    c.publicKey.length >= hop.length &&
+                    _startsWith(c.publicKey, hop) &&
                     (c.type == advTypeRepeater || c.type == advTypeRoom),
               )
               .toList();
-          if (matches.isEmpty) return hex;
+          if (matches.isEmpty) return _hopHex(hop);
           if (matches.length == 1) return matches.first.name;
           return matches.map((c) => c.name).join(' | ');
         })
-        .join(' \u2192 ');
+        .join(' → ');
+  }
+
+  /// Splits [pathBytes] into hops of [hashWidth] bytes (a trailing partial hop,
+  /// from a malformed path, is kept rather than dropped).
+  static List<List<int>> _hopGroups(List<int> pathBytes, int hashWidth) {
+    final w = hashWidth < 1 ? 1 : hashWidth;
+    final hops = <List<int>>[];
+    for (var i = 0; i < pathBytes.length; i += w) {
+      hops.add(
+        pathBytes.sublist(
+          i,
+          i + w > pathBytes.length ? pathBytes.length : i + w,
+        ),
+      );
+    }
+    return hops;
+  }
+
+  static String _hopHex(List<int> hop) =>
+      hop.map((b) => b.toRadixString(16).padLeft(2, '0').toUpperCase()).join();
+
+  static bool _startsWith(List<int> pubkey, List<int> prefix) {
+    for (var i = 0; i < prefix.length; i++) {
+      if (pubkey[i] != prefix[i]) return false;
+    }
+    return true;
   }
 }

lib/screens/chat_screen.dart

@@ -1118,8 +1118,13 @@ class _ChatScreenState extends State<ChatScreen> {
     final connector = context.read<MeshCoreConnector>();
     final allContacts = connector.allContacts;
 
-    final formattedPath = PathHelper.formatPathHex(pathBytes);
-    final resolvedNames = PathHelper.resolvePathNames(pathBytes, allContacts);
+    final hashWidth = connector.pathHashByteWidth;
+    final formattedPath = PathHelper.formatPathHex(pathBytes, hashWidth);
+    final resolvedNames = PathHelper.resolvePathNames(
+      pathBytes,
+      allContacts,
+      hashWidth,
+    );
 
     showDialog(
       context: context,

lib/widgets/path_management_dialog.dart

@@ -78,8 +78,13 @@ class _PathManagementDialogState extends State<_PathManagementDialog> {
     final connector = context.read<MeshCoreConnector>();
     final allContacts = connector.allContacts;
 
-    final formattedPath = PathHelper.formatPathHex(pathBytes);
-    final resolvedNames = PathHelper.resolvePathNames(pathBytes, allContacts);
+    final hashWidth = connector.pathHashByteWidth;
+    final formattedPath = PathHelper.formatPathHex(pathBytes, hashWidth);
+    final resolvedNames = PathHelper.resolvePathNames(
+      pathBytes,
+      allContacts,
+      hashWidth,
+    );
 
     showDialog(
       context: context,

test/helpers/path_helper_test.dart

@@ -6,11 +6,14 @@ import 'package:meshcore_open/helpers/path_helper.dart';
 import 'package:meshcore_open/models/contact.dart';
 
 Contact _contact({
-  required int firstByte,
+  required List<int> prefix,
   required String name,
   required int type,
 }) {
-  final key = Uint8List(32)..[0] = firstByte;
+  final key = Uint8List(32);
+  for (var i = 0; i < prefix.length; i++) {
+    key[i] = prefix[i];
+  }
   return Contact(
     publicKey: key,
     name: name,
@@ -22,15 +25,58 @@ Contact _contact({
 }
 
 void main() {
-  test('resolvePathNames ignores chat nodes and keeps repeater/room nodes', () {
-    final contacts = [
-      _contact(firstByte: 0xF2, name: 'MunTui', type: advTypeChat),
-      _contact(firstByte: 0x7E, name: 'zrepeater', type: advTypeRepeater),
-      _contact(firstByte: 0xBA, name: 'USS Ronald Reagan', type: advTypeRoom),
-    ];
+  group('PathHelper.formatPathHex (#154)', () {
+    test('width 1 — one hop per byte, comma-separated', () {
+      expect(PathHelper.formatPathHex([0x84, 0xab, 0x12], 1), '84,AB,12');
+    });
 
-    final resolved = PathHelper.resolvePathNames([0xF2, 0x7E, 0xBA], contacts);
+    test('width 2 — groups two bytes per hop', () {
+      expect(PathHelper.formatPathHex([0x84, 0xab, 0x12, 0x34], 2), '84AB,1234');
+    });
 
-    expect(resolved, equals('F2 → zrepeater → USS Ronald Reagan'));
+    test('width 3 — groups three bytes per hop', () {
+      expect(
+        PathHelper.formatPathHex([0x01, 0x02, 0x03, 0x04, 0x05, 0x06], 3),
+        '010203,040506',
+      );
+    });
+
+    test('trailing partial hop is kept, not dropped', () {
+      expect(PathHelper.formatPathHex([0x84, 0xab, 0x12], 2), '84AB,12');
+    });
+
+    test('empty path → empty string', () {
+      expect(PathHelper.formatPathHex([], 2), '');
+    });
+  });
+
+  group('PathHelper.resolvePathNames (#154)', () {
+    test('width 1 — resolves per-byte, ignoring chat nodes', () {
+      final contacts = [
+        _contact(prefix: [0xF2], name: 'MunTui', type: advTypeChat),
+        _contact(prefix: [0x7E], name: 'zrepeater', type: advTypeRepeater),
+        _contact(prefix: [0xBA], name: 'USS Ronald Reagan', type: advTypeRoom),
+      ];
+      final resolved = PathHelper.resolvePathNames(
+        [0xF2, 0x7E, 0xBA],
+        contacts,
+        1,
+      );
+      expect(resolved, equals('F2 → zrepeater → USS Ronald Reagan'));
+    });
+
+    test('width 2 — resolves by the full 2-byte hop prefix', () {
+      final contacts = [
+        _contact(
+          prefix: [0x7E, 0xAB],
+          name: 'zrepeater',
+          type: advTypeRepeater,
+        ),
+        // Shares the first byte but differs in the second — must NOT match.
+        _contact(prefix: [0x7E, 0x01], name: 'decoy', type: advTypeRepeater),
+      ];
+      final resolved = PathHelper.resolvePathNames([0x7E, 0xAB], contacts, 2);
+      expect(resolved, equals('zrepeater'));
+    });
   });
 }