fix: Screenshot capture in non-main thread setting

src/Sentry.Unity/ScreenshotEventProcessor.cs

@@ -26,7 +26,8 @@ public SentryEvent Process(SentryEvent @event)
         // Only ever capture one screenshot per frame
         if (Interlocked.CompareExchange(ref _isCapturingScreenshot, 1, 0) == 0)
         {
-            _sentryMonoBehaviour.StartCoroutine(CaptureScreenshotCoroutine(@event.EventId));
+            _options.LogDebug("Starting coroutine to capture a screenshot.");
+            _sentryMonoBehaviour.QueueCoroutine(CaptureScreenshotCoroutine(@event.EventId));
         }
 
         return @event;

src/Sentry.Unity/SentryMonoBehaviour.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections;
+using System.Threading;
 using Sentry.Unity.Integrations;
 using UnityEngine;
 
@@ -9,6 +10,7 @@ internal interface ISentryMonoBehaviour
 {
     event Action? ApplicationResuming;
     public Coroutine StartCoroutine(IEnumerator routine);
+    public void QueueCoroutine(IEnumerator routine);
 }
 
 /// <summary>
@@ -51,6 +53,34 @@ public void StartAwakeSpan(MonoBehaviour monoBehaviour) =>
 /// </summary>
 public partial class SentryMonoBehaviour
 {
+    private volatile IEnumerator? _queuedCoroutine;
+
+    public void QueueCoroutine(IEnumerator routine)
+    {
+        if (MainThreadData.IsMainThread())
+        {
+            StartCoroutine(routine);
+        }
+        else
+        {
+            // Fallback for issues coming from a background thread (e.g., Burst job)
+            // Screenshot will be captured in the next frame
+            _queuedCoroutine = routine;
+        }
+    }
+
+    private void Update()
+    {
+        var coroutine = _queuedCoroutine;
+        if (coroutine == null)
+        {
+            return;
+        }
+
+        _queuedCoroutine = null;
+        StartCoroutine(coroutine);
+    }
+
     /// <summary>
     /// Hook to receive an event when the application gains focus.
     /// </summary>

test/Sentry.Unity.Tests/SentryMonoBehaviourTests.cs

@@ -1,4 +1,6 @@
 using System.Collections;
+using System.Threading;
+using System.Threading.Tasks;
 using NUnit.Framework;
 using Sentry.Unity.Tests.Stubs;
 using UnityEngine;
@@ -81,4 +83,49 @@ public void UpdatePauseStatus_ResumedTwice_ApplicationResumingInvokedOnlyOnce()
         Assert.AreEqual(1, counter);
     }
 
+    [Test]
+    public void QueueCoroutine_CalledOnMainThread_StartsCoroutineImmediately()
+    {
+        var sut = _fixture.GetSut();
+        var coroutineExecuted = false;
+
+        IEnumerator TestCoroutine()
+        {
+            coroutineExecuted = true;
+            yield return null;
+        }
+
+        sut.QueueCoroutine(TestCoroutine());
+
+        Assert.IsTrue(coroutineExecuted);
+    }
+
+    [UnityTest]
+    public IEnumerator QueueCoroutine_QueuedOnBackgroundThread_StartsInUpdate()
+    {
+        var sut = _fixture.GetSut();
+        var coroutineExecuted = false;
+
+        IEnumerator TestCoroutine()
+        {
+            coroutineExecuted = true;
+            yield return null;
+        }
+
+        var thread = new Thread(() =>
+        {
+            sut.QueueCoroutine(TestCoroutine());
+        });
+
+        thread.Start();
+        thread.Join();
+
+        // Coroutine should not have started yet
+        Assert.IsFalse(coroutineExecuted);
+
+        // Wait for the coroutine to execute - trigger `Update`
+        yield return null;
+
+        Assert.IsTrue(coroutineExecuted);
+    }
 }

test/Sentry.Unity.Tests/Stubs/SentryTestMonoBehaviour.cs

@@ -16,4 +16,10 @@ internal class TestSentryMonoBehaviour : MonoBehaviour, ISentryMonoBehaviour
         StartCoroutineCalled = true;
         return base.StartCoroutine(routine);
     }
+
+    public void QueueCoroutine(IEnumerator routine)
+    {
+        // For tests, assume we're on the main thread and start immediately
+        StartCoroutine(routine);
+    }
 }