fix(dns): inherit proxy dial strategy in speedtest config (#10558)

GenMinimizedDns rebuilt route.default_domain_resolver with only a server, so speedtest configs dropped the user's Strategy4ProxyDial preference while normal configs applied it. Reuse the same resolver strategy selection for both normal and minimized configs, and add a regression test comparing both configs for UseIPv6v4.

v2rayN/ServiceLib.Tests/CoreConfig/Singbox/CoreConfigSingboxServiceTests.cs

@@ -842,4 +842,38 @@ public class CoreConfigSingboxServiceTests
         await transport.early_data_header_name.Should().BeEqualTo("Sec-WebSocket-Protocol");
         await transport.path.Should().BeEqualTo(expectedPath);
     }
+
+    [Test]
+    public async Task GenerateClientSpeedtestConfig_ShouldInheritProxyDialStrategy()
+    {
+        var config = CoreConfigTestFactory.CreateConfig(ECoreType.sing_box);
+        config.SimpleDNSItem.Strategy4ProxyDial = "UseIPv6v4";
+        CoreConfigTestFactory.BindAppManagerConfig(config);
+
+        var node = CoreConfigTestFactory.CreateSocksNode(ECoreType.sing_box);
+        var context = CoreConfigTestFactory.CreateContext(config, node, ECoreType.sing_box);
+
+        var normal = new CoreConfigSingboxService(context).GenerateClientConfigContent();
+        await normal.Success.Should().BeTrue().Because($"ret msg: {normal.Msg}");
+        var normalCfg = JsonUtils.Deserialize<SingboxConfig>(normal.Data!.ToString())!;
+        await normalCfg.route.default_domain_resolver!.strategy.Should().BeEqualTo("prefer_ipv6");
+
+        var speedtest = new CoreConfigSingboxService(context).GenerateClientSpeedtestConfig(
+        [
+            new()
+            {
+                IndexId = node.IndexId,
+                Address = node.Address,
+                Port = node.Port,
+                ConfigType = node.ConfigType,
+                Profile = node,
+                CoreType = ECoreType.sing_box,
+            }
+        ]);
+
+        await speedtest.Success.Should().BeTrue().Because($"ret msg: {speedtest.Msg}");
+        var speedtestCfg = JsonUtils.Deserialize<SingboxConfig>(speedtest.Data!.ToString())!;
+        await speedtestCfg.route.default_domain_resolver.Should().NotBeNull();
+        await speedtestCfg.route.default_domain_resolver!.strategy.Should().BeEqualTo("prefer_ipv6");
+    }
 }

v2rayN/ServiceLib/Services/CoreConfig/Singbox/SingboxDnsService.cs

@@ -542,6 +542,7 @@ public partial class CoreConfigSingboxService
         _coreConfig.route.default_domain_resolver = new()
         {
             server = Global.SingboxDirectDNSTag,
+            strategy = GetDefaultDomainResolverStrategy(),
         };
     }
 

v2rayN/ServiceLib/Services/CoreConfig/Singbox/SingboxRoutingService.cs

@@ -10,13 +10,12 @@ public partial class CoreConfigSingboxService
             var simpleDnsItem = context.SimpleDnsItem;
 
             var defaultDomainResolverTag = Global.SingboxDirectDNSTag;
-            var dialDnsStrategy = Utils.DomainStrategy4Sbox(simpleDnsItem.Strategy4ProxyDial);
+            var dialDnsStrategy = GetDefaultDomainResolverStrategy();
 
             var rawDNSItem = context.RawDnsItem;
             if (rawDNSItem is { Enabled: true })
             {
                 defaultDomainResolverTag = Global.SingboxLocalDNSTag;
-                dialDnsStrategy = rawDNSItem.DomainStrategy4Freedom.IsNullOrEmpty() ? null : rawDNSItem.DomainStrategy4Freedom;
             }
             else if (!simpleDnsItem.Strategy4Freedom.IsNullOrEmpty())
             {
@@ -613,4 +612,15 @@ public partial class CoreConfigSingboxService
 
         return tag;
     }
+
+    private string? GetDefaultDomainResolverStrategy()
+    {
+        var rawDNSItem = context.RawDnsItem;
+        if (rawDNSItem is { Enabled: true })
+        {
+            return rawDNSItem.DomainStrategy4Freedom.IsNullOrEmpty() ? null : rawDNSItem.DomainStrategy4Freedom;
+        }
+
+        return Utils.DomainStrategy4Sbox(context.SimpleDnsItem.Strategy4ProxyDial);
+    }
 }