[4.3.0 regression] `FORCE_REACT_RENDER_FOR_SETTLED_ANIMATIONS` drops the remeasure of a React commit clearing a multiline TextInput (RN 0.83, Fabric)

Description

Since upgrading reanimated 4.2.1 → 4.3.4, our chat composer's controlled multiline TextInput fails to shrink after its text is cleared, whenever the cleared text contained typed newlines. The input keeps its expanded measured height while showing the placeholder. Any later layout-dirtying commit on the input (we used a 0.01pt padding toggle) instantly restores the correct height — the shadow node is never wedged; one remeasure is dropped.

We bisected this to a single static feature flag default flipped in 4.3.0 (#8716):

Build (reanimated 4.3.4, RN 0.83.6)	Result
default flags	reproduces
USE_COMMIT_HOOK_ONLY_FOR_REACT_COMMITS: false only	still reproduces
all three 4.3.0-flipped flags at 4.2.1 values	fixed
FORCE_REACT_RENDER_FOR_SETTLED_ANIMATIONS: false only	fixed

Also verified:

• Reproduces identically on reanimated 4.5.5 + worklets 0.11.4 with default flags; fixed by the same single flag override.

Failure signature (instrumented):

• Growth works: onContentSizeChange fires per typed \n (native state-update path).
• On the clearing React commit (value → ""): no onContentSizeChange, no onLayout, and measure() reports the stale height ≥2.5s later.
• Wrap-only text (no typed newlines) clears/shrinks correctly — only the typed-newline growth path's shrink direction is affected.

What we ruled out (all tested in the reproducing app):

• Not a specific animated component. We removed, one class at a time, every useAnimatedStyle mount in the composer subtree (send button, attachment buttons/selector), the keyboard-controller animated wrappers (ancestors of the input), the mentions library (plain nested <Text> child still reproduces), and screen chrome — the bug survived every subtraction. It also reproduces on our simplest screen (a DM chat).
• Not the settled-sync render. We instrumented PropsRegistryGarbageCollector.syncPropsBackToReact: no sync fires temporally near failing clears.
• Not retained settled entries (as visible to JS): calling getSettledUpdates() immediately before the send returns an empty set — the clear commit still loses its remeasure.

Given the flag is compile-time (constexpr), the evidence points at the commit-path/registry code it gates rather than any specific registered node.

Steps to reproduce

In our production chat app (we could not distill this into a minimal project — see below):

1. Focus the chat composer (controlled multiline TextInput, text rendered as nested Text children).
2. Type a multi-line message using the return key at least twice (typed newlines matter — they grow the input through native state updates, and it is that path's shrink direction that breaks).
3. Send: the message list gains a row and the input's value is cleared in the same React commit batch.
4. The input keeps its expanded height while showing the placeholder. Any later layout-dirtying commit on the input (e.g. a 0.01pt padding change) instantly restores the correct 1-line height.

With FORCE_REACT_RENDER_FOR_SETTLED_ANIMATIONS: false (its pre-4.3.0 default) the input collapses correctly every time; no other change.

Snack or a link to a repository

We were unable to create a minimal reproduction.

Reanimated version

4.3.4 and 4.5.5 (both reproduce)

Worklets version

0.8.3 (with reanimated 4.3.4) and 0.11.4 (with 4.5.5)

React Native version

0.83.6

Platforms

iOS

JavaScript runtime

Hermes (classic 0.14.1, not Hermes V1)

Workflow

Expo Dev Client (Expo SDK 55)

Architecture

New Architecture (Fabric renderer)

Reanimated feature flags

None (defaults) — setting FORCE_REACT_RENDER_FOR_SETTLED_ANIMATIONS: false fixes the issue

React Native release level

None

Build type

Debug and Release (both reproduce)

Device

Real device and simulator

Device model

No response

Host machine

macOS

Acknowledgements

Yes