Resolve migration routine loggers from the application container

tests/Jellyfin.Server.Tests/Migrations/CodeMigrationTests.cs

@@ -20,7 +20,6 @@ public class CodeMigrationTests
             .RegisterStartupLogger()
             .AddSingleton<ApplicationSingleton>()
             .AddTransient<MigrationTransient>();
-        services.AddSingleton(services);
 
         await using var serviceProvider = services.BuildServiceProvider();
         var applicationSingleton = serviceProvider.GetRequiredService<ApplicationSingleton>();
@@ -44,6 +43,29 @@ public class CodeMigrationTests
         Assert.Same(logger.Topic, performed.Logger.Topic);
     }
 
+    [Fact]
+    public async Task Perform_DoesNotLeakTheMigrationTopic()
+    {
+        var services = new ServiceCollection()
+            .AddLogging()
+            .RegisterStartupLogger()
+            .AddSingleton<ApplicationSingleton>()
+            .AddTransient<MigrationTransient>();
+
+        await using var serviceProvider = services.BuildServiceProvider();
+        var logger = new StartupLogger(NullLogger.Instance).BeginGroup($"Test migration");
+
+        var migration = new CodeMigration(
+            typeof(TestMigration),
+            new JellyfinMigrationAttribute("2026-09-05T10:00:00", nameof(TestMigration)),
+            null);
+        await migration.Perform(serviceProvider, logger, CancellationToken.None);
+
+        // The topic belongs to the migration that ran, so loggers resolved afterwards must not still write into it.
+        Assert.Null(serviceProvider.GetRequiredService<IStartupLogger<CodeMigrationTests>>().Topic);
+        Assert.Null(new StartupLogger(NullLogger.Instance).Topic);
+    }
+
     private sealed class ApplicationSingleton : IDisposable
     {
         public bool IsDisposed { get; private set; }

tests/Jellyfin.Server.Tests/ServerSetupApp/StartupLoggerTests.cs

@@ -0,0 +1,54 @@
+using Jellyfin.Server.ServerSetupApp;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace Jellyfin.Server.Tests.ServerSetupApp;
+
+public class StartupLoggerTests
+{
+    [Fact]
+    public void BeginAmbientTopic_AttachesNewLoggersToTheTopic()
+    {
+        var migration = new StartupLogger(NullLogger.Instance).BeginGroup($"Migration");
+
+        using (StartupLogger.BeginAmbientTopic(migration.Topic))
+        {
+            Assert.Same(migration.Topic, new StartupLogger(NullLogger.Instance).Topic);
+        }
+    }
+
+    [Fact]
+    public void BeginAmbientTopic_RestoresThePreviousTopic()
+    {
+        var root = new StartupLogger(NullLogger.Instance);
+        var outer = root.BeginGroup($"Outer");
+        var inner = outer.BeginGroup($"Inner");
+
+        Assert.Null(new StartupLogger(NullLogger.Instance).Topic);
+
+        using (StartupLogger.BeginAmbientTopic(outer.Topic))
+        {
+            using (StartupLogger.BeginAmbientTopic(inner.Topic))
+            {
+                Assert.Same(inner.Topic, new StartupLogger(NullLogger.Instance).Topic);
+            }
+
+            // Leaving a nested topic has to fall back to the enclosing one, not to the setup UI root.
+            Assert.Same(outer.Topic, new StartupLogger(NullLogger.Instance).Topic);
+        }
+
+        Assert.Null(new StartupLogger(NullLogger.Instance).Topic);
+    }
+
+    [Fact]
+    public void BeginGroup_KeepsAnExplicitTopicOverTheAmbientOne()
+    {
+        var migration = new StartupLogger(NullLogger.Instance).BeginGroup($"Migration");
+        var unrelated = new StartupLogger(NullLogger.Instance).BeginGroup($"Unrelated");
+
+        using (StartupLogger.BeginAmbientTopic(migration.Topic))
+        {
+            Assert.Same(unrelated.Topic, unrelated.With(NullLogger.Instance).Topic);
+        }
+    }
+}