fix(slate-react): prevent premature flush during composition for Android handwriting input

Fixes #5979

On Android devices, handwriting input triggers compositionStart per stroke.
The RestoreDOM component was restoring childList mutations during composition,
which interrupted the IME session and caused the first stroke to be committed
prematurely (e.g., writing '我' would produce '一我').

The fix skips all DOM restoration during composition in RestoreDOM. This
preserves the user's input state while allowing Slate state updates and
onChange to fire normally.

Author: zenggenfa

.changeset/brave-dragons-write.md

@@ -0,0 +1,10 @@
+---
+'slate-react': patch
+---
+
+Fix Android handwriting input where first stroke commits prematurely (e.g., '我' becomes '一我').
+
+**Cause:** Android handwriting triggers compositionStart per stroke. The RestoreDOM component was restoring childList mutations during composition, which interrupted the IME session and caused premature commits.
+
+**Fix:** Skip all DOM restoration during composition in RestoreDOM. This preserves the user's input state while allowing Slate state updates and onChange to fire normally.
+

packages/slate-react/src/components/restore-dom/restore-dom-manager.ts

@@ -1,6 +1,6 @@
 import { RefObject } from 'react'
 import { ReactEditor } from '../../plugin/react-editor'
-import { isTrackedMutation } from 'slate-dom'
+import { isTrackedMutation, IS_COMPOSING } from 'slate-dom'
 
 export type RestoreDOMManager = {
   registerMutations: (mutations: MutationRecord[]) => void
@@ -32,6 +32,15 @@ export const createRestoreDomManager = (
 
   function restoreDOM() {
     if (bufferedMutations.length > 0) {
+      // FIX: Skip all DOM restoration during composition to prevent interrupting
+      // the IME session. This fixes Android handwriting input issue where
+      // restoring childList mutations would cause premature stroke commits.
+      // See: https://github.com/ianstormtaylor/slate/issues/5979
+      if (IS_COMPOSING.get(editor)) {
+        clear()
+        return
+      }
+
       bufferedMutations.reverse().forEach(mutation => {
         if (mutation.type === 'characterData') {
           // We don't want to restore the DOM for characterData mutations