feat: User.Id can now be overriden (set to null) in Global mode

src/Sentry/Integrations/GlobalRootScopeIntegration.cs

 } 
 Contexts.CopyTo(other.Contexts); 
 Request.CopyTo(other.Request); 
 User.CopyTo(other.User); 
 other.Release ??= Release; 
 other.Distribution ??= Distribution; 
 other.Environment ??= Environment; 
 other.TransactionName ??= TransactionName; 
 other.Level ??= Level; 
 if (Sdk.Name is not null && Sdk.Version is not null) 
 { 
     other.Sdk.Name = Sdk.Name; 
     other.Sdk.Version = Sdk.Version; 
 } 
 foreach (var package in Sdk.InternalPackages) 
 { 
     other.Sdk.AddPackage(package); 
 } 
@@ -0,0 +1,14 @@
+namespace Sentry.Integrations;
+
+internal class GlobalRootScopeIntegration : ISdkIntegration
+{
+    public void Register(IHub hub, SentryOptions options)
+    {
+        if (!options.IsGlobalModeEnabled)
+        {
+            return;
+        }
+
+        hub.ConfigureScope(scope => scope.User.Id ??= options.InstallationId);
+    }
+}

src/Sentry/Internal/Enricher.cs

@@ -12,7 +12,7 @@ internal class Enricher
 
     private readonly Lazy<Runtime> _runtimeLazy = new(() =>
     {
-        var current = PlatformAbstractions.SentryRuntime.Current;
+        var current = SentryRuntime.Current;
         return new Runtime
         {
             Name = current.Name,
@@ -36,7 +36,7 @@ public void Apply(IEventLike eventLike)
         if (!eventLike.Contexts.ContainsKey(OperatingSystem.Type))
         {
             // RuntimeInformation.OSDescription is throwing on Mono 5.12
-            if (!PlatformAbstractions.SentryRuntime.Current.IsMono())
+            if (!SentryRuntime.Current.IsMono())
             {
 #if NETFRAMEWORK
                 // RuntimeInformation.* throws on .NET Framework on macOS/Linux
@@ -58,9 +58,8 @@ public void Apply(IEventLike eventLike)
             }
         }
 
-        // SDK
         // SDK Name/Version might have be already set by an outer package
-        // e.g: ASP.NET Core can set itself as the SDK
+        // e.g.: ASP.NET Core can set itself as the SDK
         if (eventLike.Sdk.Version is null && eventLike.Sdk.Name is null)
         {
             eventLike.Sdk.Name = Constants.SdkName;
@@ -92,7 +91,12 @@ public void Apply(IEventLike eventLike)
 
             eventLike.User.IpAddress ??= DefaultIpAddress;
         }
-        eventLike.User.Id ??= _options.InstallationId;
+        // Set by the GlobalRootScopeIntegration in global mode so that it can be overridden by the user.
+        // In non-global mode (e.g. ASP.NET Core) the enricher sets it here as a fallback.
+        if (!_options.IsGlobalModeEnabled)
+        {
+            eventLike.User.Id ??= _options.InstallationId;
+        }
 
         //Apply App startup and Boot time
         eventLike.Contexts.App.StartTime ??= ProcessInfo.Instance?.StartupTime;

src/Sentry/PlatformAbstractions/FrameworkInfo.cs

@@ -36,6 +36,7 @@ public static partial class FrameworkInfo
             {528372, "4.8"},
             {528449, "4.8"},
             {533320, "4.8.1"},
-            {533325, "4.8.1"}
+            {533325, "4.8.1"},
+            {533509, "4.8.1"}
         };
 }

src/Sentry/SentryOptions.cs

@@ -220,6 +220,11 @@ internal IEnumerable<ISdkIntegration> Integrations
             }
 #endif
 
+            if ((_defaultIntegrations & DefaultIntegrations.GlobalRootScopeIntegration) != 0)
+            {
+                yield return new GlobalRootScopeIntegration();
+            }
+
             foreach (var integration in _integrations)
             {
                 yield return integration;
@@ -1362,6 +1367,7 @@ public SentryOptions()
 #if NET8_0_OR_GREATER
                                | DefaultIntegrations.SystemDiagnosticsMetricsIntegration
 #endif
+                               | DefaultIntegrations.GlobalRootScopeIntegration
                                ;
 
 #if ANDROID
@@ -1829,6 +1835,7 @@ internal enum DefaultIntegrations
 #if NET8_0_OR_GREATER
         SystemDiagnosticsMetricsIntegration = 1 << 7,
 #endif
+        GlobalRootScopeIntegration = 1 << 8,
     }
 
     internal void SetupLogging()

test/Sentry.Tests/Integrations/GlobalRootScopeIntegrationTests.cs

@@ -0,0 +1,145 @@
+using Sentry.Integrations;
+
+namespace Sentry.Tests.Integrations;
+
+public class GlobalRootScopeIntegrationTests
+{
+    [Fact]
+    public void Register_GlobalModeEnabled_SetsInstallationIdOnRootScope()
+    {
+        // Arrange
+        var options = new SentryOptions
+        {
+            Dsn = ValidDsn,
+            IsGlobalModeEnabled = true,
+            AutoSessionTracking = false
+        };
+
+        var hub = Substitute.For<IHub>();
+        var integration = new GlobalRootScopeIntegration();
+
+        // Act
+        integration.Register(hub, options);
+
+        // Assert
+        hub.Received(1).ConfigureScope(Arg.Any<Action<Scope>>());
+    }
+
+    [Fact]
+    public void Register_GlobalModeDisabled_DoesNotConfigureScope()
+    {
+        // Arrange
+        var options = new SentryOptions
+        {
+            Dsn = ValidDsn,
+            IsGlobalModeEnabled = false,
+            AutoSessionTracking = false
+        };
+
+        var hub = Substitute.For<IHub>();
+        var integration = new GlobalRootScopeIntegration();
+
+        // Act
+        integration.Register(hub, options);
+
+        // Assert
+        hub.DidNotReceive().ConfigureScope(Arg.Any<Action<Scope>>());
+    }
+
+    [Fact]
+    public void Register_GlobalModeEnabled_SetsUserIdFromInstallationId()
+    {
+        // Arrange
+        var options = new SentryOptions
+        {
+            Dsn = ValidDsn,
+            IsGlobalModeEnabled = true,
+            AutoSessionTracking = false
+        };
+
+        // Capture the action passed to ConfigureScope
+        Action<Scope> capturedAction = null;
+        var hub = Substitute.For<IHub>();
+        hub.When(h => h.ConfigureScope(Arg.Any<Action<Scope>>()))
+           .Do(call => capturedAction = call.Arg<Action<Scope>>());
+
+        var integration = new GlobalRootScopeIntegration();
+        integration.Register(hub, options);
+
+        // Apply the captured action to a real scope
+        var scope = new Scope(options);
+
+        capturedAction.Should().NotBeNull();
+        capturedAction(scope);
+
+        // The scope's User.Id should be set to the InstallationId
+        scope.User.Id.Should().Be(options.InstallationId);
+    }
+
+    [Fact]
+    public void Register_GlobalModeEnabled_DoesNotOverwriteExistingUserId()
+    {
+        // Arrange
+        var options = new SentryOptions
+        {
+            Dsn = ValidDsn,
+            IsGlobalModeEnabled = true,
+            AutoSessionTracking = false
+        };
+
+        // Capture the action passed to ConfigureScope
+        Action<Scope> capturedAction = null;
+        var hub = Substitute.For<IHub>();
+        hub.When(h => h.ConfigureScope(Arg.Any<Action<Scope>>()))
+           .Do(call => capturedAction = call.Arg<Action<Scope>>());
+
+        var integration = new GlobalRootScopeIntegration();
+        integration.Register(hub, options);
+
+        // Apply the captured action to a scope that already has a User.Id
+        var scope = new Scope(options);
+        const string existingUserId = "my-custom-user-id";
+        scope.User.Id = existingUserId;
+
+        capturedAction.Should().NotBeNull();
+        capturedAction(scope);
+
+        // The existing User.Id should not be overwritten
+        scope.User.Id.Should().Be(existingUserId);
+    }
+
+    [Fact]
+    public void Enricher_GlobalModeEnabled_DoesNotSetInstallationId()
+    {
+        // Verify the enricher no longer sets User.Id when global mode is enabled,
+        // ensuring users can clear the User.Id set by GlobalRootScopeIntegration.
+        var options = new SentryOptions { IsGlobalModeEnabled = true };
+        var enricher = new Sentry.Internal.Enricher(options);
+
+        var eventLike = Substitute.For<IEventLike>();
+        eventLike.Sdk.Returns(new SdkVersion());
+        eventLike.User = new SentryUser();
+        eventLike.Contexts = new SentryContexts();
+
+        enricher.Apply(eventLike);
+
+        eventLike.User.Id.Should().BeNull();
+    }
+
+    [Fact]
+    public void Enricher_GlobalModeDisabled_SetsInstallationIdAsFallback()
+    {
+        // Verify the enricher still sets User.Id when global mode is disabled (e.g. ASP.NET Core).
+        var options = new SentryOptions { IsGlobalModeEnabled = false };
+        var enricher = new Sentry.Internal.Enricher(options);
+
+        var eventLike = Substitute.For<IEventLike>();
+        eventLike.Sdk.Returns(new SdkVersion());
+        eventLike.User = new SentryUser();
+        eventLike.Contexts = new SentryContexts();
+
+        enricher.Apply(eventLike);
+
+        eventLike.User.Id.Should().Be(options.InstallationId);
+    }
+}

test/Sentry.Tests/SentryClientTests.cs

@@ -1,4 +1,3 @@
-using NSubstitute.ReceivedExtensions;
 using Sentry.Internal.Http;
 using BackgroundWorker = Sentry.Internal.BackgroundWorker;
 
@@ -302,10 +301,17 @@ public void CaptureEvent_EventAndScope_CopyScopeIntoEvent()
         Assert.Equal(scope.Breadcrumbs, @event.Breadcrumbs);
     }
 
-    [Fact]
+    [SkippableFact]
     public void CaptureEvent_UserIsNull_SetsFallbackUserId()
     {
+#if NET5_0_OR_GREATER
+        // In global mode the userid gets set at app startup via the GlobalRootScopeIntegration, rather than by an
+        // enricher during capture... so this functionality in SentryClient only works when IsGlobalModeEnabled is false
+        Skip.If(System.OperatingSystem.IsAndroid() || System.OperatingSystem.IsIOS(),
+            "On mobile, User.Id is set by GlobalRootScopeIntegration at startup, not the enricher.");
+#endif
         // Arrange
+        _fixture.SentryOptions.IsGlobalModeEnabled = false;
         var scope = new Scope(_fixture.SentryOptions);
         var @event = new SentryEvent();
 
@@ -1293,10 +1299,17 @@ public void CaptureTransaction_ScopeContainsAttachments_GetAppliedToHint()
         hint.Attachments.Should().Contain(attachments);
     }
 
-    [Fact]
+    [SkippableFact]
     public void CaptureTransaction_UserIsNull_SetsFallbackUserId()
     {
+#if NET5_0_OR_GREATER
+        Skip.If(System.OperatingSystem.IsAndroid() || System.OperatingSystem.IsIOS(),
+            "On mobile, User.Id is set by GlobalRootScopeIntegration at startup, not the enricher.");
+#endif
         // Arrange
+        // In global mode the userid gets set at app startup via the GlobalRootScopeIntegration, rather than by an
+        // enricher during capture... so this functionality in SentryClient only works when IsGlobalModeEnabled is false
+        _fixture.SentryOptions.IsGlobalModeEnabled = false;
         var transaction = new SentryTransaction("name", "operation")
         {
             IsSampled = true,

test/Sentry.Tests/SentryOptionsTests.Integrations_default_ones_are_properly_registered.DotNet10_0.DotNet.verified.txt

@@ -1,13 +1,4 @@
 [
-  {
-    Message: Initializing Hub for Dsn: '{0}'.,
-    Args: [
-      https://d4d82fc1c2c4032a83f3a29aa3a3aff@fake-sentry.io:65535/2147483647
-    ]
-  },
-  {
-    Message: Starting BackpressureMonitor.
-  },
   {
     Message: Registering integration: '{0}'.,
     Args: [
@@ -37,5 +28,11 @@
     Args: [
       SentryDiagnosticListenerIntegration
     ]
+  },
+  {
+    Message: Registering integration: '{0}'.,
+    Args: [
+      GlobalRootScopeIntegration
+    ]
   }
 ]

test/Sentry.Tests/SentryOptionsTests.Integrations_default_ones_are_properly_registered.DotNet10_0.Windows.DotNet.verified.txt

@@ -1,13 +1,4 @@
 [
-  {
-    Message: Initializing Hub for Dsn: '{0}'.,
-    Args: [
-      https://d4d82fc1c2c4032a83f3a29aa3a3aff@fake-sentry.io:65535/2147483647
-    ]
-  },
-  {
-    Message: Starting BackpressureMonitor.
-  },
   {
     Message: Registering integration: '{0}'.,
     Args: [
@@ -43,5 +34,11 @@
     Args: [
       WinUIUnhandledExceptionIntegration
     ]
+  },
+  {
+    Message: Registering integration: '{0}'.,
+    Args: [
+      GlobalRootScopeIntegration
+    ]
   }
 ]

test/Sentry.Tests/SentryOptionsTests.Integrations_default_ones_are_properly_registered.DotNet8_0.DotNet.verified.txt

@@ -1,13 +1,4 @@
 [
-  {
-    Message: Initializing Hub for Dsn: '{0}'.,
-    Args: [
-      https://d4d82fc1c2c4032a83f3a29aa3a3aff@fake-sentry.io:65535/2147483647
-    ]
-  },
-  {
-    Message: Starting BackpressureMonitor.
-  },
   {
     Message: Registering integration: '{0}'.,
     Args: [
@@ -37,5 +28,11 @@
     Args: [
       SentryDiagnosticListenerIntegration
     ]
+  },
+  {
+    Message: Registering integration: '{0}'.,
+    Args: [
+      GlobalRootScopeIntegration
+    ]
   }
 ]

test/Sentry.Tests/SentryOptionsTests.Integrations_default_ones_are_properly_registered.DotNet8_0.Windows.DotNet.verified.txt

@@ -1,13 +1,4 @@
 [
-  {
-    Message: Initializing Hub for Dsn: '{0}'.,
-    Args: [
-      https://d4d82fc1c2c4032a83f3a29aa3a3aff@fake-sentry.io:65535/2147483647
-    ]
-  },
-  {
-    Message: Starting BackpressureMonitor.
-  },
   {
     Message: Registering integration: '{0}'.,
     Args: [
@@ -43,5 +34,11 @@
     Args: [
       WinUIUnhandledExceptionIntegration
     ]
+  },
+  {
+    Message: Registering integration: '{0}'.,
+    Args: [
+      GlobalRootScopeIntegration
+    ]
   }
 ]