feat: Cache Unhandled session instead of sending it immediately

src/Sentry/GlobalSessionManager.cs

@@ -41,7 +41,7 @@ public GlobalSessionManager(
 
     // Take pause timestamp directly instead of referencing _lastPauseTimestamp to avoid
     // potential race conditions.
-    private void PersistSession(SessionUpdate update, DateTimeOffset? pauseTimestamp = null)
+    private void PersistSession(SessionUpdate update, DateTimeOffset? pauseTimestamp = null, bool pendingUnhandled = false)
     {
         _options.LogDebug("Persisting session (SID: '{0}') to a file.", update.Id);
 
@@ -69,7 +69,7 @@ private void PersistSession(SessionUpdate update, DateTimeOffset? pauseTimestamp
 
             var filePath = Path.Combine(_persistenceDirectoryPath, PersistedSessionFileName);
 
-            var persistedSessionUpdate = new PersistedSessionUpdate(update, pauseTimestamp);
+            var persistedSessionUpdate = new PersistedSessionUpdate(update, pauseTimestamp, pendingUnhandled);
             if (!_options.FileSystem.CreateFileForWriting(filePath, out var file))
             {
                 _options.LogError("Failed to persist session file.");
@@ -161,7 +161,10 @@ private void DeletePersistedSession()
                 status = _options.CrashedLastRun?.Invoke() switch
                 {
                     // Native crash (if native SDK enabled):
+                    // This takes priority - escalate to Crashed even if session had pending unhandled
                     true => SessionEndStatus.Crashed,
+                    // Had unhandled exception but didn't crash:
+                    _ when recoveredUpdate.PendingUnhandled => SessionEndStatus.Unhandled,
                     // Ended while on the background, healthy session:
                     _ when recoveredUpdate.PauseTimestamp is not null => SessionEndStatus.Exited,
                     // Possibly out of battery, killed by OS or user, solar flare:
@@ -185,9 +188,10 @@ private void DeletePersistedSession()
                 // If there's a callback for native crashes, check that first.
                 status);
 
-            _options.LogInfo("Recovered session: EndStatus: {0}. PauseTimestamp: {1}",
+            _options.LogInfo("Recovered session: EndStatus: {0}. PauseTimestamp: {1}. PendingUnhandled: {2}",
                 sessionUpdate.EndStatus,
-                recoveredUpdate.PauseTimestamp);
+                recoveredUpdate.PauseTimestamp,
+                recoveredUpdate.PendingUnhandled);
 
             return sessionUpdate;
         }
@@ -245,6 +249,13 @@ private void DeletePersistedSession()
 
     private SessionUpdate EndSession(SentrySession session, DateTimeOffset timestamp, SessionEndStatus status)
     {
+        // If we're ending as 'Exited' but he session has a pending 'Unhandled', end as 'Unhandled'
+        if (status == SessionEndStatus.Exited && session.HasPendingUnhandledException)
+        {
+            status = SessionEndStatus.Unhandled;
+            _options.LogDebug("Session ended as 'Unhandled' due to pending status.");
+        }
+
         if (status == SessionEndStatus.Crashed)
         {
             // increments the errors count, as crashed sessions should report a count of 1 per:
@@ -364,4 +375,18 @@ public IReadOnlyList<SessionUpdate> ResumeSession()
 
         return session.CreateUpdate(false, _clock.GetUtcNow());
     }
+
+    public void MarkSessionAsUnhandled()
+    {
+        if (_currentSession is not { } session)
+        {
+            _options.LogDebug("There is no session active. Skipping marking session as unhandled.");
+            return;
+        }
+
+        session.MarkUnhandledException();
+
+        var sessionUpdate = session.CreateUpdate(false, _clock.GetUtcNow());
+        PersistSession(sessionUpdate, pendingUnhandled: true);
+    }
 }

src/Sentry/ISessionManager.cs

@@ -17,4 +17,6 @@ internal interface ISessionManager
     public IReadOnlyList<SessionUpdate> ResumeSession();
 
     public SessionUpdate? ReportError();
+
+    public void MarkSessionAsUnhandled();
 }

src/Sentry/PersistedSessionUpdate.cs

@@ -9,10 +9,13 @@ internal class PersistedSessionUpdate : ISentryJsonSerializable
 
     public DateTimeOffset? PauseTimestamp { get; }
 
-    public PersistedSessionUpdate(SessionUpdate update, DateTimeOffset? pauseTimestamp)
+    public bool PendingUnhandled { get; }
+
+    public PersistedSessionUpdate(SessionUpdate update, DateTimeOffset? pauseTimestamp, bool pendingUnhandled = false)
     {
         Update = update;
         PauseTimestamp = pauseTimestamp;
+        PendingUnhandled = pendingUnhandled;
     }
 
     public void WriteTo(Utf8JsonWriter writer, IDiagnosticLogger? logger)
@@ -26,14 +29,20 @@ public void WriteTo(Utf8JsonWriter writer, IDiagnosticLogger? logger)
             writer.WriteString("paused", pauseTimestamp);
         }
 
+        if (PendingUnhandled)
+        {
+            writer.WriteBoolean("pendingUnhandled", PendingUnhandled);
+        }
+
         writer.WriteEndObject();
     }
 
     public static PersistedSessionUpdate FromJson(JsonElement json)
     {
         var update = SessionUpdate.FromJson(json.GetProperty("update"));
         var pauseTimestamp = json.GetPropertyOrNull("paused")?.GetDateTimeOffset();
+        var pendingUnhandled = json.GetPropertyOrNull("pendingUnhandled")?.GetBoolean() ?? false;
 
-        return new PersistedSessionUpdate(update, pauseTimestamp);
+        return new PersistedSessionUpdate(update, pauseTimestamp, pendingUnhandled);
     }
 }

src/Sentry/SentryClient.cs

@@ -352,7 +352,7 @@ private SentryId DoSendEvent(SentryEvent @event, SentryHint? hint, Scope? scope)
         {
             case SentryEvent.ExceptionType.UnhandledNonTerminal:
                 _options.LogDebug("Ending session as 'Unhandled', due to non-terminal unhandled exception.");
-                scope.SessionUpdate = _sessionManager.EndSession(SessionEndStatus.Unhandled);
+                _sessionManager.MarkSessionAsUnhandled();
                 break;
 
             case SentryEvent.ExceptionType.Unhandled:

src/Sentry/SentrySession.cs

@@ -36,6 +36,13 @@ public class SentrySession : ISentrySession
     // Start at -1 so that the first increment puts it at 0
     private int _sequenceNumber = -1;
 
+    private bool _hasPendingUnhandledException;
+
+    /// <summary>
+    /// Gets whether this session has an unhandled exception that hasn't been finalized yet.
+    /// </summary>
+    internal bool HasPendingUnhandledException => _hasPendingUnhandledException;
+
     internal SentrySession(
         SentryId id,
         string? distinctId,
@@ -74,6 +81,16 @@ public SentrySession(string? distinctId, string release, string? environment)
     /// </summary>
     public void ReportError() => Interlocked.Increment(ref _errorCount);
 
+    /// <summary>
+    /// Marks the session as having an unhandled exception without ending it.
+    /// This allows the session to continue and potentially escalate to Crashed if the app crashes.
+    /// </summary>
+    internal void MarkUnhandledException()
+    {
+        _hasPendingUnhandledException = true;
+        ReportError();
+    }
+
     internal SessionUpdate CreateUpdate(
         bool isInitial,
         DateTimeOffset timestamp,

test/Sentry.Tests/GlobalSessionManagerTests.cs

@@ -523,6 +523,184 @@
         TryRecoverPersistedSessionWithExceptionOnLastRun();
     }
 
+    [Fact]
+    public void MarkSessionAsUnhandled_ActiveSessionExists_MarksSessionAndPersists()
+    {
+        // Arrange
+        var sut = _fixture.GetSut();
+        sut.StartSession();
+        var session = sut.CurrentSession;
+
+        // Act
+        sut.MarkSessionAsUnhandled();
+
+        // Assert
+        session.Should().NotBeNull();
+        session!.HasPendingUnhandledException.Should().BeTrue();
+        session.ErrorCount.Should().Be(1);
+
+        // Session should still be active (not ended)
+        sut.CurrentSession.Should().BeSameAs(session);
+    }
+
+    [Fact]
+    public void MarkSessionAsUnhandled_NoActiveSession_LogsDebug()
+    {
+        // Arrange
+        var sut = _fixture.GetSut();
+
+        // Act
+        sut.MarkSessionAsUnhandled();
+
+        // Assert
+        _fixture.Logger.Entries.Should().Contain(e =>
+            e.Message == "No active session to mark as unhandled." &&
+            e.Level == SentryLevel.Debug);
+    }
+
+    [Fact]
+    public void MarkSessionAsUnhandled_MultipleUnhandledExceptions_OnlyCountsFirstError()
+    {
+        // Arrange
+        var sut = _fixture.GetSut();
+        sut.StartSession();
+        var session = sut.CurrentSession;
+
+        // Act
+        sut.MarkSessionAsUnhandled();
+        sut.MarkSessionAsUnhandled();
+        sut.MarkSessionAsUnhandled();
+
+        // Assert
+        session!.ErrorCount.Should().Be(1);
+    }
+
+    [Fact]
+    public void TryRecoverPersistedSession_WithPendingUnhandledAndNoCrash_EndsAsUnhandled()
+    {
+        // Arrange
+        _fixture.Options.CrashedLastRun = () => false;
+        _fixture.PersistedSessionProvider = _ => new PersistedSessionUpdate(
+            AnySessionUpdate(),
+            pauseTimestamp: null,
+            pendingUnhandled: true);
+
+        var sut = _fixture.GetSut();
+
+        // Act
+        var persistedSessionUpdate = sut.TryRecoverPersistedSession();
+
+        // Assert
+        persistedSessionUpdate.Should().NotBeNull();
+        persistedSessionUpdate!.EndStatus.Should().Be(SessionEndStatus.Unhandled);
+    }
+
+    [Fact]
+    public void TryRecoverPersistedSession_WithPendingUnhandledAndCrash_EscalatesToCrashed()
+    {
+        // Arrange
+        _fixture.Options.CrashedLastRun = () => true;
+        _fixture.PersistedSessionProvider = _ => new PersistedSessionUpdate(
+            AnySessionUpdate(),
+            pauseTimestamp: null,
+            pendingUnhandled: true);
+
+        var sut = _fixture.GetSut();
+
+        // Act
+        var persistedSessionUpdate = sut.TryRecoverPersistedSession();
+
+        // Assert
+        persistedSessionUpdate.Should().NotBeNull();
+        persistedSessionUpdate!.EndStatus.Should().Be(SessionEndStatus.Crashed);
+
+        _fixture.Logger.Entries.Should().Contain(e =>
+            e.Message.Contains("PendingUnhandled: True") &&
+            e.Level == SentryLevel.Info);
+    }
+
+    [Fact]
+    public void TryRecoverPersistedSession_WithPendingUnhandledAndPauseTimestamp_EscalatesToCrashedIfCrashed()
+    {
+        // Arrange - Session was paused AND had pending unhandled, then crashed
+        _fixture.Options.CrashedLastRun = () => true;
+        var pausedTimestamp = DateTimeOffset.Now;
+        _fixture.PersistedSessionProvider = _ => new PersistedSessionUpdate(
+            AnySessionUpdate(),
+            pausedTimestamp,
+            pendingUnhandled: true);
+
+        var sut = _fixture.GetSut();
+
+        // Act
+        var persistedSessionUpdate = sut.TryRecoverPersistedSession();
+
+        // Assert
+        // Crash takes priority over all other end statuses
+        persistedSessionUpdate.Should().NotBeNull();
+        persistedSessionUpdate!.EndStatus.Should().Be(SessionEndStatus.Crashed);
+    }
+
+    [Fact]
+    public void EndSession_WithPendingUnhandledException_PreservesUnhandledStatus()
+    {
+        // Arrange
+        var sut = _fixture.GetSut();
+        sut.StartSession();
+        sut.MarkSessionAsUnhandled();
+
+        // Act - Try to end normally with Exited status
+        var sessionUpdate = sut.EndSession(SessionEndStatus.Exited);
+
+        // Assert - Should be overridden to Unhandled
+        sessionUpdate.Should().NotBeNull();
+        sessionUpdate!.EndStatus.Should().Be(SessionEndStatus.Unhandled);
+        sessionUpdate.ErrorCount.Should().Be(1);
+    }
+
+    [Fact]
+    public void EndSession_WithPendingUnhandledAndCrashedStatus_UsesCrashedStatus()
+    {
+        // Arrange
+        var sut = _fixture.GetSut();
+        sut.StartSession();
+        sut.MarkSessionAsUnhandled();
+
+        // Act - Explicitly end with Crashed status
+        var sessionUpdate = sut.EndSession(SessionEndStatus.Crashed);
+
+        // Assert - Crashed status takes priority
+        sessionUpdate.Should().NotBeNull();
+        sessionUpdate!.EndStatus.Should().Be(SessionEndStatus.Crashed);
+        sessionUpdate.ErrorCount.Should().Be(1);
+    }
+
+    [Fact]
+    public void SessionEscalation_CompleteFlow_UnhandledThenCrash()
+    {
+        // Arrange - Simulate complete flow
+        var sut = _fixture.GetSut();
+        sut.StartSession();
+        var originalSessionId = sut.CurrentSession!.Id;
+
+        // Act 1: Mark as unhandled (game encounters exception but continues)
+        sut.MarkSessionAsUnhandled();
+
+        // Assert: Session still active with pending flag
+        sut.CurrentSession.Should().NotBeNull();
+        sut.CurrentSession!.Id.Should().Be(originalSessionId);
+        sut.CurrentSession.HasPendingUnhandledException.Should().BeTrue();
+
+        // Act 2: Recover on next launch with crash detected
+        _fixture.Options.CrashedLastRun = () => true;
+        var recovered = sut.TryRecoverPersistedSession();
+
+        // Assert: Session escalated from Unhandled to Crashed
+        recovered.Should().NotBeNull();
+        recovered!.EndStatus.Should().Be(SessionEndStatus.Crashed);
+        recovered.Id.Should().Be(originalSessionId);
+    }
+
     // A session update (of which the state doesn't matter for the test):
     private static SessionUpdate AnySessionUpdate()
         => new(

test/Sentry.Tests/Sentry.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(CurrentTfms)</TargetFrameworks>
+    <TargetFrameworks>$(CurrentTfms);net48</TargetFrameworks>
     <TargetFrameworks Condition="'$(NO_ANDROID)' == ''">$(TargetFrameworks);$(LatestAndroidTfm);$(PreviousAndroidTfm)</TargetFrameworks>
     <TargetFrameworks Condition="'$(NO_IOS)' == '' And $([MSBuild]::IsOSPlatform('OSX'))">$(TargetFrameworks);$(LatestIosTfm);$(PreviousIosTfm)</TargetFrameworks>
     <TargetFrameworks Condition="'$(NO_MACCATALYST)' == '' And $([MSBuild]::IsOSPlatform('OSX'))">$(TargetFrameworks);$(LatestMacCatalystTfm);$(PreviousMacCatalystTfm)</TargetFrameworks>