perf: Skip the pre-draw repair on frames without React mounts

[MatiPl01]

The pre-draw repair re-asserts every running platform transition on every frame, but React can only overwrite an animated value on frames where it wrote props. A UIManagerListener records mounts and the repair returns immediately on all other frames, so the walk over running transitions happens at write rate rather than at the display refresh rate.

That matters most after a transition settles: a persistent hold keeps its entry, so without the gate every later frame the window draws keeps walking the map. Measured on an emulator during a 3s transition, 201 of 240 pre-draw callbacks returned early.

Synchronous updates run their mount item inline (FabricUIManager.synchronouslyUpdateViewOnUIThread), bypassing MountItemDispatcher, so no listener fires for them even though opacity is one of the props they carry. They therefore open the gate explicitly, which makes the invariant true by construction rather than by coincidence. Measured on device, such writes are rare and always landed on a frame where a mount had already opened the gate, so this is insurance rather than an observed fix.

Identical in content to #10168, which this replaces. That one was based on the head branch of #10061, and closing #10061 instead of merging it left the base pointing at a branch with no live PR, so merging would not have reached main. GitHub refuses to change the base of a pull request that belongs to a stack, so recreating it was the only way to target main.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 237cb581-0cdc-42de-86c9-da6a64761b83

📥 Commits

Reviewing files that changed from the base of the PR and between 267eb5f and dd32131.

📒 Files selected for processing (2)

• packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/NativeProxy.kt
• packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSPlatformTransitionsManager.kt

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved synchronization of UI property updates with platform transitions.
  • Prevented unnecessary transition repair work when no React-driven updates occur.
  • Improved handling of transition state during component mounting and lifecycle changes.

Walkthrough

The change adds React mount-write tracking to CSSPlatformTransitionsManager. NativeProxy reports synchronous UI property writes. Transition repair now runs only when React writes occurred since the previous draw.

Changes

CSS transition reconciliation

Layer / File(s)	Summary
React mount write tracking packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSPlatformTransitionsManager.kt	The manager registers a FabricUIManager listener, records React writes on the UI thread, and removes the listener during invalidation.
Synchronous write notification and repair gating packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/NativeProxy.kt, packages/react-native-reanimated/android/src/main/java/com/swmansion/reanimated/css/CSSPlatformTransitionsManager.kt	NativeProxy reports synchronous prop writes. The manager skips repair when no React write occurred since the previous draw while preserving active animator state.

Estimated code review effort: 2 (Simple) | ~10 minutes

Mergeability Score: ⚪ Minimal · up to dd321

The change limits transition repair work to frames where React may have written props, while preserving coverage for synchronous updates. No actionable merge-blocking risk remains beyond normal checks and review.

Possibly related PRs

• software-mansion/react-native-reanimated#10060: Modifies the same transition integration in NativeProxy.kt and CSSPlatformTransitionsManager.kt.
• software-mansion/react-native-reanimated#10090: Extends CSSPlatformTransitionsManager transition repair behavior.
• software-mansion/react-native-reanimated#10242: Updates CSS transition handling for React and UI property writes.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly summarizes the main change: skipping pre-draw repair on frames without React mounts.
Description check	✅ Passed	The description accurately explains mount-gated repair, synchronous updates, performance impact, and the pull request context.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch @matipl01/android-css-mount-gated-repair

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