Incorrect font scaling with adjustsFontSizeToFitWidth

Description

Sometimes <Text> element that has both lineHeight and adjustsFontSizeToFit sometimes shrinks the text even if there is enough place for it to be rendered.

It seems to happen when there is a fractional height separator in the layout.
There seem to be two problems:

1. The font is scaled although there is enough space for the text to be rendered with the original font-size
2. minimumFontScale seems not to be respected

Steps to reproduce

Here is minimal repro code of the app (also available in the expo snack)

When running the app the 2nd and 7th text element seem to be wrongly scaled (changing the number of element, the height of the separator or even fast-refresh seem to alter which elements are scaled incorrectly).

import { SafeAreaView, StyleSheet, Text, View } from "react-native";

const styles = StyleSheet.create({
  container: {
    alignItems: "center",
    justifyContent: "center",
  },
  text: {
    fontSize: 12,
    lineHeight: 20,
    width: 200,
  },
  separator: {
    height: 0.5,
    width: 200,
    backgroundColor: "green",
  },
});

const Test = () => (
  <Text
    style={styles.text}
    numberOfLines={1}
    adjustsFontSizeToFit
    minimumFontScale={0.8}
  >
    XXXXXXXXX
  </Text>
);

export default function App() {
  return (
    <SafeAreaView>
      <View style={styles.container}>
        <View style={styles.separator} />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
        <Test />
      </View>
    </SafeAreaView>
  );
}

React Native Version

0.79.5

Affected Platforms

Runtime - iOS

Output of npx @react-native-community/cli info

System:
  OS: macOS 15.5
  CPU: (14) arm64 Apple M4 Max
  Memory: 115.22 MB / 36.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 20.15.1
    path: ~/.nvm/versions/node/v20.15.1/bin/node
  Yarn:
    version: 1.22.22
    path: ~/.nvm/versions/node/v20.15.1/bin/yarn
  npm:
    version: 10.7.0
    path: ~/.nvm/versions/node/v20.15.1/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/alexander.vakrilov/.rvm/gems/ruby-3.3.6/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.0
      - iOS 18.0
      - macOS 15.0
      - tvOS 18.0
      - visionOS 2.0
      - watchOS 11.0
  Android SDK: Not Found
IDEs:
  Android Studio: 2024.1 AI-241.18034.62.2411.12071903
  Xcode:
    version: 16.0/16A242d
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.11
    path: /usr/bin/javac
  Ruby:
    version: 3.3.6
    path: /Users/alexander.vakrilov/.rvm/rubies/ruby-3.3.6/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 19.0.0
    wanted: 19.0.0
  react-native:
    installed: 0.79.5
    wanted: 0.79.5
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

No crash

MANDATORY Reproducer

https://snack.expo.dev/@vakrilov/0e4781

Screenshots and Videos

まず、iOS で必須の Expo Snack 再現コードを実行し、テキスト要素を小数の高さのセパレーター、および lineHeight、adjustsFontSizeToFit、minimumFontScale の設定と比較します。不正なスケーリングを再現できたら、ネイティブのテキストレイアウト経路を追跡します。スペースが十分にある場合にテキストが縮小されず、minimumFontScale が尊重されれば完了です。