test(audience-sample): hide log pane on Linux PlayMode to skip llvmpipe rasterisation

PR 765 captured a player profile that showed the Unity 6 Linux cells
spending roughly 4.5 seconds per frame in Gfx.PresentFrame self time on
the render thread. Camera.Render was 2 ms and UI.RenderOverlays 1.45 ms
per frame; the 4.5 sec is llvmpipe walking the deferred command buffer
and rasterising approximately 2920 batches and 7520 triangles per
frame, almost all of which are UI Toolkit log rows generated by the
SampleApp's accumulating log pane.

LinuxLogPaneSuppression registers a SceneManager.sceneLoaded handler
that sets the log ScrollView to display:none after each scene load.
display:none skips layout and render but keeps elements in the visual
tree, so HasLogEntry (which walks contentContainer.Children() and
inspects userData by reference) still observes log rows correctly.

Engages only on StandaloneLinux64 builds via #if UNITY_STANDALONE_LINUX.
Mac and Windows PlayMode runs are unaffected.

Author: ImmutableJeffrey

examples/audience/Assets/SampleApp/Tests/Runtime/LinuxLogPaneSuppression.cs

@@ -0,0 +1,68 @@
+#nullable enable
+
+#if UNITY_STANDALONE_LINUX
+using NUnit.Framework;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+using UnityEngine.UIElements;
+
+namespace Immutable.Audience.Samples.SampleApp.Tests
+{
+    // Linux PlayMode test optimisation: hide the SampleApp log pane so UI
+    // Toolkit does not generate triangles for its rows during test runs.
+    //
+    // The player profile captured on PR 765 showed Render Thread spending
+    // roughly 4.5 seconds per frame in Gfx.PresentFrame self time on Unity
+    // 6 Linux cells, with ~2920 batches and ~7520 triangles per frame.
+    // Camera.Render is 2 ms, UI.RenderOverlays 1.45 ms; the rest is
+    // llvmpipe rasterising the deferred command buffer at present time.
+    // The bulk of those triangles come from the log pane, which
+    // accumulates one row per logged event over the course of a session.
+    //
+    // display:none keeps elements in the visual tree (so VisualElement.Q
+    // and contentContainer.Children() still find them) but skips layout
+    // and render entirely. Tests assert on log entries via userData on
+    // each row, which is reference-based, not layout-based, so the
+    // assertions stay correct.
+    //
+    // Engages only on StandaloneLinux64 builds (gated by the #if). Mac
+    // and Windows PlayMode runs are unaffected.
+    [SetUpFixture]
+    public sealed class LinuxLogPaneSuppression
+    {
+        [OneTimeSetUp]
+        public void RegisterSceneHook()
+        {
+            SceneManager.sceneLoaded += HideLogPane;
+        }
+
+        [OneTimeTearDown]
+        public void DeregisterSceneHook()
+        {
+            SceneManager.sceneLoaded -= HideLogPane;
+        }
+
+        // Re-fires for every scene load. The SampleApp's UIDocument runs
+        // its UI initialisation in Awake, so by the time sceneLoaded
+        // fires the log ScrollView is in the tree and ready to be
+        // styled. The hook is idempotent across loads.
+        private static void HideLogPane(Scene scene, LoadSceneMode mode)
+        {
+            var sample = Object.FindFirstObjectByType<AudienceSample>(FindObjectsInactive.Include);
+            if (sample == null) return;
+
+            var doc = sample.GetComponent<UIDocument>();
+            if (doc == null) return;
+
+            var root = doc.rootVisualElement;
+            if (root == null) return;
+
+            var log = root.Q<ScrollView>(SampleAppUi.LogScrollView);
+            if (log == null) return;
+
+            log.style.display = new StyleEnum<DisplayStyle>(DisplayStyle.None);
+            Debug.Log("[LinuxLogPaneSuppression] log pane hidden for Linux PlayMode test run.");
+        }
+    }
+}
+#endif