[Android] Fix Switch Shadow Does Not Follow Thumb when Toggle On or Off

[Dhivya-SF4094]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details:

When a shadow property is applied to a Switch control, the shadow does not move with the thumb when toggling the switch on or off. The shadow remains in its initial position and does not update to follow the thumb’s movement, causing a visual inconsistency.

Root Cause:

• In Android hardware-accelerated rendering, each view maintains its own RenderNode, which stores a cached display list of drawing operations. When a view calls invalidate(), Android re-records only that view’s display list, while parent views continue replaying their cached display lists unless they are explicitly invalidated.

• PlatformWrapperView wraps controls such as Switch and Slider and renders shadows as part of its own display list, separate from the child control. During animations like a Switch toggle, the child control (SwitchCompat) invalidates itself every frame to redraw the moving thumb. Android therefore updates only the child’s display list, while PlatformWrapperViewcontinues replaying its cached display list. As a result, the shadow remains visually stuck at its previous position instead of following the animated thumb.

• This issue occurred because Android uses different parent invalidation callbacks depending on API level:
  API 26+ → onDescendantInvalidated()
  API 21–25 → invalidateChildInParent()

• PlatformWrapperView did not override either callback, so it never received descendant invalidation notifications and never refreshed its cached shadow rendering during child animations.

Description of change:

The fix adds overrides for both descendant invalidation paths in PlatformWrapperView:

• onDescendantInvalidated() for API 26+
• invalidateChildInParent() for API 21–25

When a descendant view invalidates, the wrapper now invalidates itself as well, forcing its display list to be re-recorded so the shadow is redrawn at the correct position during each animation frame.

To avoid unnecessary work, a cached hasShadow flag is maintained and checked before triggering wrapper invalidation. This ensures that wrappers used only for clipping or borders do not incur additional redraw overhead. Only wrappers with active shadows participate in the extra invalidation logic.
This fix resolves stale shadow rendering consistently across all supported Android API levels in MAUI.

Validated the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Fixes

Fixes #30046

Screenshots

Before	After
30046_BeforeFix.mov	30046_AfterFix.mov

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 35623

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 35623"

[kubaflo]

/review -b feature/refactor-copilot-yml

[MauiBot]

🤖 Automated review — alternative fix proposed

The expert-reviewer evaluation compared the PR fix against #2 automatically generated candidates and selected try-fix-2 as the strongest fix.

Why: try-fix-2 won because it passed the Android STEP 6a regression run and is the most general passing alternative, keeping hardware acceleration enabled while refreshing the shadow wrapper when the child is dirty. The PR-derived fixes remain production-attractive but are ranked lower because the supplied gate failed.

Please consider applying the candidate diff below (or use it as guidance). Once you push an update, this workflow will re-trigger and re-evaluate.

Candidate diff (`try-fix-2`)

diff --git a/src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java b/src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java
index 17f24676ba..20c5a620b5 100644
--- a/src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java
+++ b/src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java
@@ -17,6 +17,7 @@ import android.graphics.Shader;
 
 
 import android.view.View;
+import android.view.ViewTreeObserver;
 
 import androidx.annotation.NonNull;
 
@@ -48,6 +49,8 @@ public abstract class PlatformWrapperView extends PlatformContentViewGroup {
     private Shader shadowShader;
     private boolean shadowInvalidated = true;
     private boolean hasClip = false;
+    private boolean hasShadow = false;
+    private ViewTreeObserver.OnPreDrawListener shadowPreDrawListener;
 
     private float offsetX = 0;
     private float offsetY = 0;
@@ -97,13 +100,15 @@ public abstract class PlatformWrapperView extends PlatformContentViewGroup {
     }
 
     private void onShadowStyleChanged() {
-        if (this.shadowStyle.getPaintType() == PlatformPaintType.NONE) {
+        this.hasShadow = (this.shadowStyle.getPaintType() != PlatformPaintType.NONE);
+        if (!this.hasShadow) {
             this.shadowPaint = null;
             this.shadowCanvas = null;
             if (this.shadowBitmap != null) {
                 this.bitmapPool.put(this.shadowBitmap);
                 this.shadowBitmap = null;
             }
+            uninstallShadowPreDrawListener();
         } else {
             this.shadowCanvas = new Canvas();
             this.shadowPaint = new Paint();
@@ -115,15 +120,70 @@ public abstract class PlatformWrapperView extends PlatformContentViewGroup {
             if (this.radius > 0) {
                 this.shadowPaint.setMaskFilter(new BlurMaskFilter(this.radius, BlurMaskFilter.Blur.NORMAL));
             }
+            installShadowPreDrawListener();
         }
 
         this.shadowInvalidated = true;
         invalidate();
     }
 
+    // Watches the global draw pipeline. When the child has a pending invalidation
+    // (e.g., SwitchCompat animating its thumb), the wrapper's own RenderNode is NOT
+    // automatically re-recorded — only the child's RenderNode is. This means our cached
+    // shadow bitmap (and the wrapper's display-list shadow draw call) become stale relative
+    // to the child's new content.
+    //
+    // Rather than intercepting descendant invalidation callbacks (which fires for every
+    // child invalidation, shadow or not), we observe the draw pipeline and only invalidate
+    // when (a) shadow is active AND (b) the child is actually dirty. shadowInvalidated is
+    // also marked so drawShadowViaDispatchDraw regenerates the bitmap from the new child
+    // content on the next dispatchDraw pass.
+    private void installShadowPreDrawListener() {
+        if (this.shadowPreDrawListener != null) {
+            return;
+        }
+        this.shadowPreDrawListener = new ViewTreeObserver.OnPreDrawListener() {
+            @Override
+            public boolean onPreDraw() {
+                if (hasShadow && getChildCount() > 0) {
+                    View child = getChildAt(0);
+                    if (child.isDirty()) {
+                        shadowInvalidated = true;
+                        invalidate();
+                    }
+                }
+                return true;
+            }
+        };
+        ViewTreeObserver vto = getViewTreeObserver();
+        if (vto.isAlive()) {
+            vto.addOnPreDrawListener(this.shadowPreDrawListener);
+        }
+    }
+
+    private void uninstallShadowPreDrawListener() {
+        if (this.shadowPreDrawListener == null) {
+            return;
+        }
+        ViewTreeObserver vto = getViewTreeObserver();
+        if (vto.isAlive()) {
+            vto.removeOnPreDrawListener(this.shadowPreDrawListener);
+        }
+        this.shadowPreDrawListener = null;
+    }
+
+    @Override
+    protected void onAttachedToWindow() {
+        super.onAttachedToWindow();
+        if (this.hasShadow) {
+            installShadowPreDrawListener();
+        }
+    }
+
     @Override
     protected void onDetachedFromWindow() {
         super.onDetachedFromWindow();
+        uninstallShadowPreDrawListener();
         this.shadowInvalidated = true;
         if (this.shadowBitmap != null) {
             this.bitmapPool.put(this.shadowBitmap);

[MauiBot]

🤖 AI Summary

👋 @Dhivya-SF4094 — new AI review results are available. Please review the latest session below.

📊 Review Session — b59502c · Updated fix for api25 and below · 2026-05-27 15:15 UTC

🚦 Gate — Test Before & After Fix

Gate Result: ❌ FAILED

Platform: ANDROID · Base: main · Merge base: b0ea772f

🩺 Test does not reproduce the bug — ran the same in both states (PASS without fix, PASS with fix). The repro test is not exercising the issue. Strengthen the test before reviewing the fix.

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
🖥️ Issue30046 Issue30046	❌ PASS — 501s	✅ PASS — 490s

🔴 Without fix — 🖥️ Issue30046: PASS ❌ · 501s

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Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:06:40.03
Broadcasting: Intent { act=android.intent.action.CLOSE_SYSTEM_DIALOGS flg=0x400000 }
Broadcast completed: result=0
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Test run for /home/vsts/work/1/s/artifacts/bin/Controls.TestCases.Android.Tests/Debug/net10.0/Controls.TestCases.Android.Tests.dll (.NETCoreApp,Version=v10.0)
VSTest version 18.0.1 (x64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.18]   Discovering: Controls.TestCases.Android.Tests
[xUnit.net 00:00:00.54]   Discovered:  Controls.TestCases.Android.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /home/vsts/work/1/s/artifacts/bin/Controls.TestCases.Android.Tests/Debug/net10.0/Controls.TestCases.Android.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 05/27/2026 12:31:48 FixtureSetup for Issue30046(Android)
>>>>> 05/27/2026 12:31:49 SwitchShadowFollowsThumbOnToggle Start
>>>>> 05/27/2026 12:31:55 SwitchShadowFollowsThumbOnToggle Stop
  Passed SwitchShadowFollowsThumbOnToggle [6 s]
NUnit Adapter 4.5.0.0: Test execution complete
Results File: /home/vsts/work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue30046.trx

Test Run Successful.
Total tests: 1
     Passed: 1
 Total time: 19.9217 Seconds
>>> TRX_RESULT_FILE: /home/vsts/work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue30046.trx

🟢 With fix — 🖥️ Issue30046: PASS ✅ · 490s

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Build succeeded.
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Time Elapsed 00:06:31.73
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VSTest version 18.0.1 (x64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.11]   Discovering: Controls.TestCases.Android.Tests
[xUnit.net 00:00:00.31]   Discovered:  Controls.TestCases.Android.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /home/vsts/work/1/s/artifacts/bin/Controls.TestCases.Android.Tests/Debug/net10.0/Controls.TestCases.Android.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 05/27/2026 12:39:59 FixtureSetup for Issue30046(Android)
>>>>> 05/27/2026 12:40:00 SwitchShadowFollowsThumbOnToggle Start
>>>>> 05/27/2026 12:40:06 SwitchShadowFollowsThumbOnToggle Stop
  Passed SwitchShadowFollowsThumbOnToggle [6 s]
NUnit Adapter 4.5.0.0: Test execution complete
Results File: /home/vsts/work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue30046.trx

Test Run Successful.
Total tests: 1
     Passed: 1
 Total time: 17.9395 Seconds
>>> TRX_RESULT_FILE: /home/vsts/work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue30046.trx

⚠️ Failure Details

• ❌ Issue30046 PASSED without fix (should fail) — tests don't catch the bug

📁 Fix files reverted (2 files)

• eng/pipelines/ci-copilot.yml
• src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java

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🧪 UI Tests — Shadow,Switch

Detected UI test categories: Shadow,Switch

❌ Deep UI tests — 41 passed, 1 failed across 2 categories on platform-pool agent (replaces in-process counts above).

🧪 UI Test Execution Results (deep, platform pool)

Category	Tests	Snapshot diffs
Shadow	17/19 (1 ❌)	1 diff PNG
Switch	24/24 ✓	—

❌ Shadow — 1 failed test

Shadow_SetEnabledStateToFalse_VerifyScreenshot

VisualTestUtils.VisualTestFailedException : 
Snapshot different than baseline: Shadow_SetEnabledStateToFalse_VerifyScreenshot.png (0.52% difference)
If the correct baseline has changed (this isn't a a bug), then update the baseline image.
See test attachment or download the build artifacts to get the new snapshot file.

More info: https://aka.ms/visual-test-workflow
at Microsoft.Maui.TestCases.Tests.UITest.VerifyScreenshot(String name, Nullable`1 retryDelay, Nullable`1 retryTimeout, Int32 cropLeft, Int32 cropRight, Int32 cropTop, Int32 cropBottom, Double tolerance) in /_/src/Controls/tests/TestCases.Shared.Tests/UITest.cs:line 296
   at Microsoft.Maui.TestCases.Tests.ShadowFeatureTests.Shadow_SetEnabledStateToFalse_VerifyScreenshot() in /_/src/Controls/tests/TestCases.Shared.Tests/Tests/FeatureMatrix/ShadowFeatureTests.cs:line 163
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Objec
...

📎 Download drop-deep-uitests artifact (TRX + snapshot diffs)

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🔍 Regression Cross-Reference

🟢 No implementation files modified — skipping regression cross-reference.

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🔍 Pre-Flight — Context & Validation

Issue: #30046 - [Android] Switch Shadow Does Not Follow Thumb when Toggle On or Off
PR: #35623 - [Android] Fix Switch Shadow Does Not Follow Thumb when Toggle On or Off
Platforms Affected: Android
Files Changed: 1 implementation, 4 test

Key Findings

• Issue [Android] Switch Shadow Does Not Follow Thumb when Toggle On or Off #30046 reports that an Android Switch with a Shadow leaves the shadow in the original thumb position when toggled on/off.
• PR [Android] Fix Switch Shadow Does Not Follow Thumb when Toggle On or Off  #35623 changes PlatformWrapperView.java so descendant invalidation forces the wrapper shadow display list to be invalidated when an active shadow exists.
• Regression coverage adds an Android issue page, Android screenshot baselines, and a shared UI test in category Switch.
• Gate result supplied by caller: Gate ❌ FAILED — tests did NOT behave as expected. Gate was not re-run in this phase.

Code Review Summary

Verdict: NEEDS_CHANGES
Confidence: high
Errors: 1 | Warnings: 1 | Suggestions: 0

Key code review findings:

• ❌ src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30046.cs:1 adds an Android-only screenshot test unconditionally in the shared UI test project. The host page is Android-only and only Android baselines were added, so non-Android discovery can fail unless the test is gated with #if ANDROID or cross-platform baselines/support are added.
• ⚠️ src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30046.cs:26 and :33 take screenshots immediately after the Toggled label update, which may race the visual thumb/shadow animation. A screenshot retryTimeout would better match existing UI test patterns for animation-sensitive assertions.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #35623	Override Android descendant invalidation paths in PlatformWrapperView and invalidate the wrapper when hasShadow is true.	❌ FAILED (Gate supplied by caller)	src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformWrapperView.java, UI test files	Original PR

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🔬 Code Review — Deep Analysis

Code Review — PR #35623

Independent Assessment

What this changes: Android PlatformWrapperView now tracks whether it has an active shadow and, when shadowed descendants invalidate, forces the wrapper itself to invalidate so its cached shadow drawing is recomputed. The PR also adds an Android issue page plus an Appium screenshot test that toggles a shadowed Switch on and off.
Inferred motivation: The child Switch thumb animates independently of the wrapper shadow; descendant invalidation needs to dirty the wrapper display list so the shadow follows the moving thumb.

Reconciliation with PR Narrative

Author claims: The PR fixes issue #30046 by handling both Android invalidation paths (onDescendantInvalidated on API 26+ and invalidateChildInParent on API 21–25), guarded by a cached hasShadow flag, and validates on Android.
Agreement/disagreement: The code matches the stated root cause and approach. I did not find a concrete problem in the PlatformWrapperView implementation. The added regression test, however, is Android-specific while living in the shared issue test project without platform gating.

Findings

❌ Error — Android-only screenshot test is discovered on non-Android platforms

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30046.cs:1 adds the test unconditionally in the shared UI test project, while the host page is marked PlatformAffected.Android and the PR only adds Android screenshot baselines. The issue list does not filter by PlatformAffected; _IssuesUITest searches/navigates by issue text, so this test can be discovered in iOS/Windows/MacCatalyst runs and then fail due missing/nonmatching baselines for SwitchShadowInOnState and SwitchShadowBackInOffState. Please gate the test with #if ANDROID (as other Android-only issue tests do) or add full cross-platform support and baselines.

⚠️ Warning — Screenshot assertions may race the Switch animation

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30046.cs:26 and :33 verify screenshots immediately after the status label text changes. That text confirms the Toggled event, not that the thumb/shadow animation has visually settled. The UI test guidance recommends using retryTimeout for animation-sensitive screenshot tests; consider VerifyScreenshotOrSetException(ref exception, "SwitchShadowInOnState", retryTimeout: TimeSpan.FromSeconds(2)) and the same for the off-state screenshot.

Devil's Advocate

The unconditional test might not fail in every CI leg if only Android Switch tests are selected, but the shared test project is intended to be cross-platform unless explicitly gated, and there are no non-Android baselines here. The animation warning is less severe because VerifyScreenshot has a built-in Android delay and one retry, but using retryTimeout is the repository-preferred pattern for visual animation stability.

Verdict: NEEDS_CHANGES

Confidence: high
Summary: The production Android invalidation fix appears sound and scoped, and CI checks currently show no failing GitHub check runs. The PR should still change the new shared UI test before merge so it cannot run on unsupported platforms; adding screenshot retry timeout would also reduce flakiness.

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🔧 Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix	Use LAYER_TYPE_SOFTWARE for shadow-active wrappers to bypass hardware display-list caching.	✅ PASS	1 file	Works, but self-review found a major performance tradeoff because all shadowed wrapper subtrees lose hardware acceleration. Not better than PR.
2	try-fix	Add a shadow-scoped OnPreDrawListener that invalidates the wrapper when the immediate child is dirty.	✅ PASS	1 file	Works, but adds listener lifecycle/per-frame complexity and may miss deeper dynamic descendants. Not better than PR.
3	try-fix	Add a Switch-specific timed parent-chain invalidation loop during toggle animation, plus Android-only test gating/retry timeout.	✅ PASS	2 files	Works for the test, but expert review found it is a narrower timed polling workaround with broader redraw cost and lifecycle risks. Not better than PR.
4	try-fix	Regenerate dispatch-draw shadow cache when the child has transient state.	✅ PASS	1 file	Works for the test, but expert review found it depends on parent redraw/transient-state semantics and is less complete than descendant invalidation. Not better than PR.
5	try-fix	Hook Switch thumb/track drawable invalidation and invalidate the immediate shadow wrapper.	✅ PASS	3 files	Works for the test, but expert review found it is narrower and not demonstrably correct for all Switch/shared-wrapper invalidation paths. Not better than PR.
PR	PR #35623	Override Android descendant invalidation paths and invalidate the wrapper when hasShadow is true.	❌ FAILED (Gate supplied by caller)	5 files	Original PR; production fix appears sound but test has platform-gating/flakiness concerns.

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	1	No	All plausible approaches had been explored; remaining variations were trivial.
claude-opus-4.7	1	No	PR uses canonical descendant-invalidation hook; alternatives add polling/listeners, Switch-specific hacks, software-layer cost, or parent redraw assumptions.
gpt-5.3-codex	1	No	PR approach is the canonical Android mechanism for parent reaction to subtree visual changes.
gpt-5.5	1	Yes	Suggested hooking Switch drawable invalidation at the source; explored as candidate 5.
claude-opus-4.6	2	No	Remaining options are trivial variants or equivalent/worse tradeoffs.
claude-opus-4.7	2	No	Remaining alternatives are broader redraw costs or narrower Switch hooks.
gpt-5.3-codex	2	No	No unexplored general-purpose invalidation propagation path better than the PR callback override.
gpt-5.5	2	No	PR already targets the shared invalidation/display-list root cause with the narrowest generic hook.

Exhausted: Yes
Selected Fix: PR's production fix — it is the most robust general fix for the shared Android wrapper invalidation root cause. The PR should still address the pre-flight test concerns: gate the shared UI test to Android and add screenshot retry timeout.

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📋 Report — Final Recommendation

Comparative Report — PR #35623

Gate evidence

The supplied gate result for the raw PR fix failed: Issue30046 passed both without and with the PR production fix, so the PR regression test did not prove the bug. Per instruction, candidates with failed regression tests are ranked lower than candidates that passed them.

Candidate ranking

Rank	Candidate	Regression result	Assessment
1	try-fix-2	PASS	Best passing alternative. It keeps hardware acceleration enabled and fixes the shared wrapper shadow invalidation problem generically by observing child dirtiness before draw. Reviewer findings are moderate and acceptable compared with the stronger risks in other passing alternatives.
2	try-fix-5	PASS	Passing and targeted at Switch drawable invalidation, but narrower than the shared wrapper root cause and not proven for every Switch/shared-wrapper invalidation path.
3	try-fix-4	PASS	Passing, but depends on dispatchDraw() already being re-entered and child.hasTransientState() being a complete proxy for visual changes; less complete than invalidation propagation.
4	try-fix-3	PASS	Passing, and it includes Android test gating/retry timeout, but the production fix is a Switch-specific timed parent-chain invalidation loop with broader redraw and lifecycle risk.
5	try-fix-1	PASS	Passing, but disables hardware acceleration for all shadowed wrapper subtrees and carries a major performance risk.
6	pr-plus-reviewer	NOT VERIFIED / inherits failed PR gate	Production fix remains the most direct root-cause fix, and the sandbox patch addresses concrete test feedback. However, no passing gate evidence exists and the expert reviewer’s critical finding remains that the test did not prove the bug.
7	pr	FAILED	Production fix appears sound, but the supplied gate failed and the test has Android gating/flakiness/proof concerns.

Winner

try-fix-2 is the single winning candidate because it passed the STEP 6a Android regression run and is the most general passing alternative. It avoids the major performance cost of try-fix-1, the Switch-specific/polling limitations of try-fix-3 and try-fix-5, and the parent-redraw/transient-state assumption in try-fix-4.

The PR-derived candidates remain attractive from a production-design perspective, but the explicit ranking rule requires failed-gate PR fixes to rank below candidates with passing regression evidence.

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