feat(CSS): route shadowColor transitions to the Android platform path

[MatiPl01]

Note

This pull request was authored by AI on behalf of @MatiPl01.

Summary

Add shadowColor to the properties the Android platform animation path drives. React Native applies it as a plain view property (setOutlineAmbientShadowColor and setOutlineSpotShadowColor, Android 9+), so it goes through the same ColorBlendWriter as backgroundColor; both shadow channels are written because RN's setter writes both. Below API 28 the writer declines and the property stays on the C++ loop.

The path is chosen at build time. ANDROID_CSS_PLATFORM_TRANSITIONS is a static feature flag compiled into the native code (off by default, on in fabric-example); with it on, a shadowColor transition runs on the platform path as long as the view has no onCSSTransition* callbacks, which keep every property on the loop. Nothing switches at runtime and no re-render is involved.

Recording

All three boxes together, then each one alone:

shadow_demo_v3_small.mp4

Solo modes

Only the selected row animates, the others stay red:

Changelog

Entry added under New features in packages/react-native-reanimated/CHANGELOG.md.

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• packages/react-native-reanimated/CHANGELOG.md
• packages/react-native-reanimated/Common/cpp/reanimated/CSS/utils/platform.h

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• packages/react-native-reanimated/CHANGELOG.md

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📝 Walkthrough

Walkthrough

Adds shadowColor to Android platform-property routing. On Android API 28 and newer, CSSPropertyWriter creates a color blend writer that reads the ambient shadow color and writes both ambient and spot shadow colors. Older Android versions keep the property on the C++ path. The changelog records the new behavior.

Priority: ⬇️ Low

Change: Feature

Merge Risk: ⚪ Minimal · up to 52e5d

The Android shadowColor platform path preserves older-version fallback and matches existing cross-platform routing behavior, so the change is mergeable.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: routing shadowColor CSS transitions through the Android platform path.
Description check	✅ Passed	The description directly explains the shadowColor platform-path changes, API 28 behavior, feature flag, callback condition, testing evidence, and changelog update.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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