fix: Windows same-host mDNS discovery + surface received mDNS queries in diagnostics

lib/services/debug_diagnostics.dart

@@ -3,6 +3,7 @@ import 'dart:io' show Platform;
 import 'package:bike_control/main.dart' show recordError;
 import 'package:bike_control/services/mdns_discovery_scan.dart';
 import 'package:flutter/foundation.dart';
+import 'package:prop/mdns/mdns_responder.dart' show MdnsQueryLogEntry;
 import 'package:prop/mdns/service_advertiser.dart';
 import 'package:prop/utils/advertised_service_registry.dart';
 import 'package:prop/utils/network_address.dart';
@@ -53,6 +54,10 @@ class DebugDiagnostics {
   final List<TcpServerInfo> servers;
   final PermissionsSnapshot permissions;
 
+  /// mDNS queries our responder saw. Empty on the nsd backend (iOS), where the
+  /// OS responder handles queries and never tells us about them.
+  final List<MdnsQueryLogEntry> recentQueries;
+
   const DebugDiagnostics({
     required this.advertised,
     required this.backend,
@@ -63,6 +68,7 @@ class DebugDiagnostics {
     required this.addressReport,
     required this.servers,
     required this.permissions,
+    this.recentQueries = const [],
   });
 
   static Future<DebugDiagnostics> gather({
@@ -119,6 +125,7 @@ class DebugDiagnostics {
       addressReport: addressReport,
       servers: servers,
       permissions: permissions,
+      recentQueries: isResponder ? advertiser.recentQueries : const [],
     );
   }
 
@@ -167,6 +174,22 @@ class DebugDiagnostics {
       b.writeln('    ${c.interfaceName}/${c.address} = ${c.score}${tags.isEmpty ? '' : ' (${tags.join(', ')})'}');
     }
 
+    // "Did the trainer app on this machine ask us anything, and did we answer?"
+    // A same-host querier shows up with the advertised address as its source.
+    // No entries at all means the failure is upstream of this responder.
+    b.writeln('  mDNS queries received:');
+    if (recentQueries.isEmpty) {
+      b.writeln('    (none)');
+    } else {
+      for (final q in recentQueries) {
+        final at = q.at.toIso8601String().split('T').last.split('.').first;
+        b.writeln(
+          '    $at ${q.source}:${q.sourcePort} ${q.wantsUnicast ? 'QU' : 'QM'} '
+          '${q.questions.join(', ')} → ${q.reply}',
+        );
+      }
+    }
+
     b.writeln('  TCP servers:');
     if (servers.isEmpty) {
       b.writeln('    (none)');

test/services/debug_diagnostics_test.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 import 'package:bike_control/services/debug_diagnostics.dart';
 import 'package:bike_control/services/mdns_discovery_scan.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:prop/mdns/mdns_responder.dart' show MdnsQueryLogEntry;
 import 'package:prop/utils/advertised_service_registry.dart';
 import 'package:prop/utils/network_address.dart';
 
@@ -78,4 +79,46 @@ void main() {
     expect(diag.toText(), contains('Discovered on network:'));
     expect(diag.toText(), contains('(skipped)'));
   });
+
+  group('mDNS queries received', () {
+    DebugDiagnostics withQueries(List<MdnsQueryLogEntry> queries) => DebugDiagnostics(
+          advertised: const [],
+          backend: 'responder',
+          hostLabel: 'bikecontrol-3f2a',
+          holdsMulticastLock: false,
+          discovered: const [],
+          discoveryRan: false,
+          addressReport: const AddressPickReport(chosen: null, candidates: []),
+          servers: const [],
+          permissions: const PermissionsSnapshot(localNetworkInferred: null),
+          recentQueries: queries,
+        );
+
+    test('renders each query with its source, QU bit and how it was answered', () {
+      final text = withQueries([
+        MdnsQueryLogEntry(
+          at: DateTime(2026, 7, 30, 9, 41, 12),
+          source: '192.168.178.92',
+          sourcePort: 5353,
+          wantsUnicast: true,
+          questions: const ['PTR _wahoo-fitness-tnp._tcp.local'],
+          answeredUnicast: true,
+          answeredMulticast: true,
+        ),
+      ]).toText();
+
+      expect(text, contains('mDNS queries received:'));
+      expect(text, contains('192.168.178.92:5353'));
+      expect(text, contains('QU'));
+      expect(text, contains('PTR _wahoo-fitness-tnp._tcp.local'));
+      expect(text, contains('unicast+multicast'));
+    });
+
+    test('says so when nothing has queried us', () {
+      // The decisive line for "the trainer app on this machine cannot see
+      // BikeControl": if no query ever arrived, the problem is upstream of our
+      // responder, not in how we answer.
+      expect(withQueries(const []).toText(), contains('(none)'));
+    });
+  });
 }