fix(#156): width-aware node-prefix matching (repeater highlight, map anchors/overlaps)

Three routing-match sites keyed/compared nodes by only the first
public-key byte, which collides when two nodes share a first byte on a
2-/3-byte path-hash mesh:

- DirectRepeater.matchesPathStart() replaces the 1-byte
  `pubkeyFirstByte == pathBytes.first` direct-repeater check in
  chat_screen and path_management_dialog (x3 each).
- map _computeGuessedLocations packs the full configured-width prefix as
  the repeaterByHash key and looks up the contact-side hop at the same
  width — was keying publicKey[0] but reading pathBytes.last, a silent
  miss at width>1 that stopped location-guessing on multi-byte meshes.
- map _filterContactsBySettings overlap detection compares the
  configured-width prefix via _samePubkeyPrefix (was publicKey.first).

Adds DirectRepeater.matchesPathStart unit tests. Bumps build to +46 for
the combined path-hash sweep test binary (b46: #151+#154+#155+#156).

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

lib/connector/meshcore_connector.dart

@@ -68,6 +68,16 @@ class DirectRepeater {
   String get prefixHex =>
       pubkeyPrefix.map((b) => b.toRadixString(16).padLeft(2, '0')).join();
 
+  /// True if [pathBytes] begins with this repeater's full configured-width
+  /// prefix — the width-aware replacement for a 1-byte first-hop match. (#156)
+  bool matchesPathStart(List<int> pathBytes) {
+    if (pathBytes.length < pubkeyPrefix.length) return false;
+    for (var i = 0; i < pubkeyPrefix.length; i++) {
+      if (pathBytes[i] != pubkeyPrefix[i]) return false;
+    }
+    return true;
+  }
+
   void update(double newSNR) {
     snr = newSNR;
     lastUpdated = DateTime.now();

lib/screens/chat_screen.dart

@@ -813,16 +813,13 @@ class _ChatScreenState extends State<ChatScreen> {
             pathsWithRepeaters = paths.map((path) {
               final isDirectRepeater =
                   directRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  directRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  directRepeater.matchesPathStart(path.pathBytes);
               final isSecondDirectRepeater =
                   secondDirectRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  secondDirectRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  secondDirectRepeater.matchesPathStart(path.pathBytes);
               final isThirdDirectRepeater =
                   thirdDirectRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  thirdDirectRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  thirdDirectRepeater.matchesPathStart(path.pathBytes);
 
               int ranking = -1;
               Color color = Colors.grey;

lib/screens/map_screen.dart

@@ -269,7 +269,7 @@ class _MapScreenState extends State<MapScreen> {
             )
             .join(',');
         final cacheKey =
-            '$filteredKeys|$anchorKeys|${pathHistory.version}:${connector.currentSf}:${connector.currentBwHz}:${connector.currentTxPower}:${settings.mapShowGuessedLocations}';
+            '$filteredKeys|$anchorKeys|${pathHistory.version}:${connector.currentSf}:${connector.currentBwHz}:${connector.currentTxPower}:${connector.pathHashByteWidth}:${settings.mapShowGuessedLocations}';
         if (cacheKey != _guessedLocationsCacheKey) {
           _guessedLocationsCacheKey = cacheKey;
           _cachedGuessedLocations = settings.mapShowGuessedLocations
@@ -278,6 +278,7 @@ class _MapScreenState extends State<MapScreen> {
                   allContactsWithLocation,
                   pathHistory,
                   maxRangeKm,
+                  connector.pathHashByteWidth,
                 )
               : [];
         }
@@ -698,19 +699,28 @@ class _MapScreenState extends State<MapScreen> {
     List<Contact> withLocation,
     PathHistoryService pathHistory,
     double? maxRangeKm,
+    int pathHashByteWidth,
   ) {
-    // Index known-location repeaters by their 1-byte hash.
-    // null value = two repeaters share the same hash byte (ambiguous collision).
-    final repeaterByHash = <int, Contact?>{};
+    // Index known-location repeaters by their configured-width hash prefix,
+    // packed into an int key. null value = two repeaters share that prefix
+    // (ambiguous collision). Width-aware so 2-/3-byte meshes disambiguate
+    // instead of colliding on the first byte alone. (#156)
+    final w = pathHashByteWidth < 1 ? 1 : pathHashByteWidth;
+    int packPrefix(List<int> bytes, int start) {
+      var v = 0;
+      for (var i = 0; i < w; i++) {
+        v = (v << 8) | bytes[start + i];
+      }
+      return v;
+    }
 
+    final repeaterByHash = <int, Contact?>{};
     for (final c in withLocation) {
-      if (c.type == advTypeRepeater) {
-        if (repeaterByHash.containsKey(c.publicKey[0])) {
-          repeaterByHash[c.publicKey[0]] =
-              null; // collision: can't disambiguate
-        } else {
-          repeaterByHash[c.publicKey[0]] = c;
-        }
+      if (c.type == advTypeRepeater && c.publicKey.length >= w) {
+        final key = packPrefix(c.publicKey, 0);
+        repeaterByHash[key] = repeaterByHash.containsKey(key)
+            ? null // collision: can't disambiguate
+            : c;
       }
     }
 
@@ -736,12 +746,13 @@ class _MapScreenState extends State<MapScreen> {
             .getRecentPaths(contact.publicKeyHex)
             .map((r) => r.pathBytes),
       ];
-      final lastHopBytes = <int>{};
       for (final pathBytes in pathSets) {
-        if (pathBytes.isEmpty) continue;
-        final lastHop = pathBytes.last;
-        lastHopBytes.add(lastHop);
-        final r = repeaterByHash[lastHop];
+        if (pathBytes.length < w) continue;
+        // Anchor on the contact-side hop. Paths are stored device-side-first
+        // (Contact.path is the reversed wire path), so the contact-side repeater
+        // is the trailing w bytes — the same hop the 1-byte code read via
+        // pathBytes.last, just widened to the configured width.
+        final r = repeaterByHash[packPrefix(pathBytes, pathBytes.length - w)];
         if (r != null) anchorSet.add(LatLng(r.latitude!, r.longitude!));
       }
 
@@ -965,6 +976,13 @@ class _MapScreenState extends State<MapScreen> {
   }) {
     List<Contact> filtered = [];
     bool addContact = false;
+    // Overlap detection compares the configured-width hash prefix, so 2-/3-byte
+    // meshes only flag true routing collisions, not incidental 1-byte ones. (#156)
+    int overlapWidth = 1;
+    if (settings.mapShowOverlaps) {
+      final hw = context.read<MeshCoreConnector>().pathHashByteWidth;
+      overlapWidth = hw < 1 ? 1 : hw;
+    }
     for (final contact in contacts) {
       addContact = false;
       if (!contact.hasLocation && !noLocations) {
@@ -999,7 +1017,7 @@ class _MapScreenState extends State<MapScreen> {
             .where(
               (c) =>
                   c.publicKeyHex != contact.publicKeyHex &&
-                  c.publicKey.first == contact.publicKey.first &&
+                  _samePubkeyPrefix(c, contact, overlapWidth) &&
                   (c.type == advTypeRepeater || c.type == advTypeRoom) &&
                   (contact.type == advTypeRepeater ||
                       contact.type == advTypeRoom),
@@ -1020,6 +1038,16 @@ class _MapScreenState extends State<MapScreen> {
     return filtered;
   }
 
+  /// True if two contacts share their first [width] public-key bytes — the
+  /// width-aware replacement for a 1-byte first-byte comparison. (#156)
+  bool _samePubkeyPrefix(Contact a, Contact b, int width) {
+    if (a.publicKey.length < width || b.publicKey.length < width) return false;
+    for (var i = 0; i < width; i++) {
+      if (a.publicKey[i] != b.publicKey[i]) return false;
+    }
+    return true;
+  }
+
   List<Marker> _buildMarkers(
     List<Contact> contacts,
     settings, {

lib/widgets/path_management_dialog.dart

@@ -203,16 +203,13 @@ class _PathManagementDialogState extends State<_PathManagementDialog> {
             paths.map((path) {
               final isDirectRepeater =
                   directRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  directRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  directRepeater.matchesPathStart(path.pathBytes);
               final isSecondDirectRepeater =
                   secondDirectRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  secondDirectRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  secondDirectRepeater.matchesPathStart(path.pathBytes);
               final isThirdDirectRepeater =
                   thirdDirectRepeater != null &&
-                  path.pathBytes.isNotEmpty &&
-                  thirdDirectRepeater.pubkeyFirstByte == path.pathBytes.first;
+                  thirdDirectRepeater.matchesPathStart(path.pathBytes);
 
               int ranking = -1;
               Color color = Colors.grey;

pubspec.yaml

@@ -16,7 +16,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 # https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
 # In Windows, build-name is used as the major, minor, and patch parts
 # of the product and file versions while build-number is used as the build suffix.
-version: 1.1.2-rc.1+45
+version: 1.1.2-rc.1+46
 
 environment:
   sdk: ^3.9.2

test/connector/direct_repeater_ranking_test.dart

@@ -86,4 +86,30 @@ void main() {
       expect(r.prefixHex, '84');
     });
   });
+
+  group('DirectRepeater.matchesPathStart (#156)', () {
+    DirectRepeater repeater(List<int> prefix) => DirectRepeater(
+      pubkeyFirstByte: prefix.first,
+      pubkeyPrefix: Uint8List.fromList(prefix),
+      snr: 12.0,
+    );
+
+    test('width 1 — matches on the single prefix byte', () {
+      expect(repeater([0x84]).matchesPathStart([0x84, 0xab]), isTrue);
+      expect(repeater([0x84]).matchesPathStart([0x99]), isFalse);
+    });
+
+    test('width 2 — both bytes must match, so a 1-byte collision misses', () {
+      final r = repeater([0x84, 0xab]);
+      expect(r.matchesPathStart([0x84, 0xab, 0xc1]), isTrue);
+      // Shares only the first byte — the #156 collision that a 1-byte match
+      // would have falsely accepted.
+      expect(r.matchesPathStart([0x84, 0x99]), isFalse);
+    });
+
+    test('a path shorter than the prefix never matches', () {
+      expect(repeater([0x84, 0xab]).matchesPathStart([0x84]), isFalse);
+      expect(repeater([0x84]).matchesPathStart(<int>[]), isFalse);
+    });
+  });
 }