fix: preserve CHANGE_ME qBit placeholder sections on config save

src/Torrentarr.Core/Configuration/ConfigurationLoader.cs

@@ -1755,9 +1755,10 @@ private string GenerateTomlContent(TorrentarrConfig config)
         }
         sb.AppendLine();
 
-        // All qBit instances — "qBit" written first (primary), then additional [qBit-XXX]
+        // All qBit instances — "qBit" written first (primary), then additional [qBit-XXX].
+        // Include CHANGE_ME placeholders so multi-instance stubs survive WebUI round-trips.
         var orderedQbit = config.QBitInstances
-            .Where(kv => !string.IsNullOrEmpty(kv.Value.Host) && kv.Value.Host != "CHANGE_ME")
+            .Where(kv => !string.IsNullOrEmpty(kv.Value.Host))
             .OrderBy(kv => kv.Key == "qBit" ? 0 : 1).ThenBy(kv => kv.Key);
 
         foreach (var (name, qbit) in orderedQbit)

src/Torrentarr.Host/Program.cs

@@ -2626,7 +2626,7 @@ static async Task<IResult> HandleTestConnection(TestConnectionRequest req, Torre
     var currentObj = new Newtonsoft.Json.Linq.JObject();
     currentObj["Settings"] = Newtonsoft.Json.Linq.JObject.FromObject(cfg.Settings, serializer);
     currentObj["WebUI"] = Newtonsoft.Json.Linq.JObject.FromObject(cfg.WebUI, serializer);
-    foreach (var (key, qbit) in cfg.QBitInstances.Where(kv => kv.Value.Host != "CHANGE_ME"))
+    foreach (var (key, qbit) in cfg.QBitInstances)
         currentObj[key] = Newtonsoft.Json.Linq.JObject.FromObject(qbit, serializer);
     foreach (var (key, arr) in cfg.ArrInstances)
         currentObj[key] = Newtonsoft.Json.Linq.JObject.FromObject(arr, serializer);

tests/Torrentarr.Core.Tests/Configuration/ConfigurationLoaderTests.cs

@@ -671,6 +671,33 @@ public void SaveConfig_PreservesQBitTrackers()
         reloaded.Settings.LoopSleepTimer.Should().Be(10);
     }
 
+    [Fact]
+    public void SaveConfig_PreservesChangeMeQBitPlaceholderSection()
+    {
+        WriteToml("""
+            [Settings]
+            LoopSleepTimer = 5
+
+            [qBit]
+            Host = "localhost"
+            Port = 8080
+
+            [qBit-seedbox]
+            Host = "CHANGE_ME"
+            Port = 8080
+            """);
+
+        var loader = new ConfigurationLoader(_tempFilePath);
+        var config = loader.Load();
+        config.Settings.LoopSleepTimer = 10;
+        loader.SaveConfig(config);
+
+        var reloaded = new ConfigurationLoader(_tempFilePath).Load();
+        reloaded.QBitInstances.Should().ContainKey("qBit-seedbox");
+        reloaded.QBitInstances["qBit-seedbox"].Host.Should().Be("CHANGE_ME");
+        reloaded.Settings.LoopSleepTimer.Should().Be(10);
+    }
+
     [Fact]
     public void Save_WebUI_WritesAuthBooleans()
     {

tests/Torrentarr.Host.Tests/Api/ConfigPlaceholderPreservationTests.cs

@@ -0,0 +1,44 @@
+using FluentAssertions;
+using System.Net;
+using System.Text;
+using System.Text.Json;
+using Xunit;
+
+namespace Torrentarr.Host.Tests.Api;
+
+/// <summary>
+/// Regression: CHANGE_ME qBit placeholder sections must survive unrelated POST /web/config saves.
+/// </summary>
+[Collection("HostWeb")]
+public class ConfigPlaceholderPreservationTests : IClassFixture<MultiQBitPlaceholderWebApplicationFactory>
+{
+    private readonly MultiQBitPlaceholderWebApplicationFactory _factory;
+
+    public ConfigPlaceholderPreservationTests(MultiQBitPlaceholderWebApplicationFactory factory)
+    {
+        _factory = factory;
+    }
+
+    [Fact]
+    public async Task PostConfig_UnrelatedChange_PreservesChangeMeQBitSeedboxStubOnDisk()
+    {
+        _factory.SetConfigEnv();
+        var client = _factory.CreateClientWithApiToken();
+
+        var payload = new
+        {
+            changes = new Dictionary<string, object>
+            {
+                ["settings.loopSleepTimer"] = 12
+            }
+        };
+        var content = new StringContent(JsonSerializer.Serialize(payload), Encoding.UTF8, "application/json");
+
+        var response = await client.PostAsync("/web/config", content);
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var savedToml = await File.ReadAllTextAsync(_factory.TempConfigPath);
+        savedToml.Should().Contain("[qBit-seedbox]");
+        savedToml.Should().Contain("Host = \"CHANGE_ME\"");
+    }
+}

tests/Torrentarr.Host.Tests/Api/TorrentarrWebApplicationFactory.cs

@@ -365,6 +365,44 @@ protected override void Dispose(bool disposing)
     }
 }
 
+/// <summary>Factory with configured qBit plus a CHANGE_ME placeholder qBit-seedbox stub.</summary>
+public class MultiQBitPlaceholderWebApplicationFactory : TorrentarrWebApplicationFactory
+{
+    public MultiQBitPlaceholderWebApplicationFactory() => RewriteConfigFile();
+
+    protected override string GetTestConfigToml() => """
+        [Settings]
+        ConfigVersion = "6.12.2"
+        LoopSleepTimer = 5
+        FailedCategory = "failed"
+        RecheckCategory = "recheck"
+        PingURLS = ["one.one.one.one"]
+
+        [WebUI]
+        Host = "0.0.0.0"
+        Port = 6969
+        Token = "test-api-token"
+        AuthDisabled = true
+        LocalAuthEnabled = false
+        OIDCEnabled = false
+        LiveArr = false
+
+        [qBit]
+        Host = "localhost"
+        Port = 8080
+        UserName = "admin"
+        Password = "adminpass"
+        ManagedCategories = ["radarr"]
+
+        [qBit-seedbox]
+        Host = "CHANGE_ME"
+        Port = 8080
+        UserName = "CHANGE_ME"
+        Password = "CHANGE_ME"
+        ManagedCategories = []
+        """;
+}
+
 /// <summary>Factory with Radarr, Sonarr, Lidarr, and qBit sections for catalog/validation endpoint tests.</summary>
 public class ArrCatalogWebApplicationFactory : TorrentarrWebApplicationFactory
 {