Split diff horizontal scroll into platform-specific components

Use Metro .web.tsx resolution to separate native gesture arbitration
(RNGH ScrollView, waitFor, closeGestureRef) from web (plain RN ScrollView),
fixing text selection drag on desktop web.

packages/app/src/components/diff-scroll.tsx

@@ -0,0 +1,85 @@
+import { useState, useCallback, useEffect, useId, useRef } from "react";
+import {
+  type LayoutChangeEvent,
+  type NativeSyntheticEvent,
+  type NativeScrollEvent,
+  type StyleProp,
+  type ViewStyle,
+} from "react-native";
+import { ScrollView, type ScrollView as ScrollViewType } from "react-native-gesture-handler";
+import { useHorizontalScrollOptional } from "@/contexts/horizontal-scroll-context";
+import { useExplorerSidebarAnimation } from "@/contexts/explorer-sidebar-animation-context";
+
+interface DiffScrollProps {
+  children: React.ReactNode;
+  scrollViewWidth: number;
+  onScrollViewWidthChange: (width: number) => void;
+  style?: StyleProp<ViewStyle>;
+  contentContainerStyle?: StyleProp<ViewStyle>;
+}
+
+export function DiffScroll({
+  children,
+  scrollViewWidth,
+  onScrollViewWidthChange,
+  style,
+  contentContainerStyle,
+}: DiffScrollProps) {
+  const [isAtLeftEdge, setIsAtLeftEdge] = useState(true);
+  const horizontalScroll = useHorizontalScrollOptional();
+  const scrollId = useId();
+  const scrollViewRef = useRef<ScrollViewType>(null);
+
+  // Get the close gesture ref from animation context (may not be available outside sidebar)
+  let closeGestureRef: React.MutableRefObject<any> | undefined;
+  try {
+    const animation = useExplorerSidebarAnimation();
+    closeGestureRef = animation.closeGestureRef;
+  } catch {
+    // Not inside ExplorerSidebarAnimationProvider, which is fine
+  }
+
+  // Register/unregister scroll offset tracking
+  useEffect(() => {
+    if (!horizontalScroll) return;
+    // Start at 0 (not scrolled)
+    horizontalScroll.registerScrollOffset(scrollId, 0);
+    return () => {
+      horizontalScroll.unregisterScrollOffset(scrollId);
+    };
+  }, [horizontalScroll, scrollId]);
+
+  const handleScroll = useCallback(
+    (event: NativeSyntheticEvent<NativeScrollEvent>) => {
+      const offsetX = event.nativeEvent.contentOffset.x;
+      // Track if we're at the left edge (with small threshold for float precision)
+      setIsAtLeftEdge(offsetX <= 1);
+      if (horizontalScroll) {
+        horizontalScroll.registerScrollOffset(scrollId, offsetX);
+      }
+    },
+    [horizontalScroll, scrollId],
+  );
+
+  return (
+    <ScrollView
+      ref={scrollViewRef}
+      horizontal
+      nestedScrollEnabled
+      showsHorizontalScrollIndicator
+      bounces={false}
+      style={style}
+      contentContainerStyle={contentContainerStyle}
+      onScroll={handleScroll}
+      scrollEventThrottle={16}
+      onLayout={(e: LayoutChangeEvent) => onScrollViewWidthChange(e.nativeEvent.layout.width)}
+      // When at left edge, wait for close gesture to fail before scrolling.
+      // The close gesture fails quickly on leftward swipes (failOffsetX=-10),
+      // so scrolling left works normally. On rightward swipes, close gesture
+      // activates and closes the sidebar.
+      waitFor={isAtLeftEdge && closeGestureRef?.current ? closeGestureRef : undefined}
+    >
+      {children}
+    </ScrollView>
+  );
+}

packages/app/src/components/diff-scroll.web.tsx

@@ -0,0 +1,29 @@
+import { ScrollView, type LayoutChangeEvent, type StyleProp, type ViewStyle } from "react-native";
+
+interface DiffScrollProps {
+  children: React.ReactNode;
+  scrollViewWidth: number;
+  onScrollViewWidthChange: (width: number) => void;
+  style?: StyleProp<ViewStyle>;
+  contentContainerStyle?: StyleProp<ViewStyle>;
+}
+
+export function DiffScroll({
+  children,
+  onScrollViewWidthChange,
+  style,
+  contentContainerStyle,
+}: DiffScrollProps) {
+  return (
+    <ScrollView
+      horizontal
+      nestedScrollEnabled
+      showsHorizontalScrollIndicator
+      style={style}
+      contentContainerStyle={contentContainerStyle}
+      onLayout={(e: LayoutChangeEvent) => onScrollViewWidthChange(e.nativeEvent.layout.width)}
+    >
+      {children}
+    </ScrollView>
+  );
+}

packages/app/src/components/git-diff-pane.tsx

@@ -2,7 +2,6 @@ import {
   useState,
   useCallback,
   useEffect,
-  useId,
   useMemo,
   useRef,
   memo,
@@ -20,7 +19,6 @@ import {
   type NativeSyntheticEvent,
   type NativeScrollEvent,
 } from "react-native";
-import { ScrollView, type ScrollView as ScrollViewType } from "react-native-gesture-handler";
 import { StyleSheet, UnistylesRuntime, useUnistyles } from "react-native-unistyles";
 import AsyncStorage from "@react-native-async-storage/async-storage";
 import {
@@ -44,8 +42,7 @@ import {
 } from "@/hooks/use-checkout-diff-query";
 import { useCheckoutStatusQuery } from "@/hooks/use-checkout-status-query";
 import { useCheckoutPrStatusQuery } from "@/hooks/use-checkout-pr-status-query";
-import { useHorizontalScrollOptional } from "@/contexts/horizontal-scroll-context";
-import { useExplorerSidebarAnimation } from "@/contexts/explorer-sidebar-animation-context";
+import { DiffScroll } from "./diff-scroll";
 import {
   darkHighlightColors,
   lightHighlightColors,
@@ -262,41 +259,6 @@ function DiffFileBody({
   testID?: string;
 }) {
   const [scrollViewWidth, setScrollViewWidth] = useState(0);
-  const [isAtLeftEdge, setIsAtLeftEdge] = useState(true);
-  const horizontalScroll = useHorizontalScrollOptional();
-  const scrollId = useId();
-  const scrollViewRef = useRef<ScrollViewType>(null);
-
-  // Get the close gesture ref from animation context (may not be available outside sidebar)
-  let closeGestureRef: React.MutableRefObject<any> | undefined;
-  try {
-    const animation = useExplorerSidebarAnimation();
-    closeGestureRef = animation.closeGestureRef;
-  } catch {
-    // Not inside ExplorerSidebarAnimationProvider, which is fine
-  }
-
-  // Register/unregister scroll offset tracking
-  useEffect(() => {
-    if (!horizontalScroll) return;
-    // Start at 0 (not scrolled)
-    horizontalScroll.registerScrollOffset(scrollId, 0);
-    return () => {
-      horizontalScroll.unregisterScrollOffset(scrollId);
-    };
-  }, [horizontalScroll, scrollId]);
-
-  const handleScroll = useCallback(
-    (event: NativeSyntheticEvent<NativeScrollEvent>) => {
-      const offsetX = event.nativeEvent.contentOffset.x;
-      // Track if we're at the left edge (with small threshold for float precision)
-      setIsAtLeftEdge(offsetX <= 1);
-      if (horizontalScroll) {
-        horizontalScroll.registerScrollOffset(scrollId, offsetX);
-      }
-    },
-    [horizontalScroll, scrollId],
-  );
 
   return (
     <View
@@ -364,29 +326,18 @@ function DiffFileBody({
         }
 
         return (
-          <ScrollView
-            ref={scrollViewRef}
-            horizontal
-            nestedScrollEnabled
-            showsHorizontalScrollIndicator
-            bounces={false}
+          <DiffScroll
+            scrollViewWidth={scrollViewWidth}
+            onScrollViewWidthChange={setScrollViewWidth}
             style={styles.diffContent}
             contentContainerStyle={styles.diffContentInner}
-            onScroll={handleScroll}
-            scrollEventThrottle={16}
-            onLayout={(e) => setScrollViewWidth(e.nativeEvent.layout.width)}
-            // When at left edge, wait for close gesture to fail before scrolling.
-            // The close gesture fails quickly on leftward swipes (failOffsetX=-10),
-            // so scrolling left works normally. On rightward swipes, close gesture
-            // activates and closes the sidebar.
-            waitFor={isAtLeftEdge && closeGestureRef?.current ? closeGestureRef : undefined}
           >
             <View
               style={[styles.linesContainer, scrollViewWidth > 0 && { minWidth: scrollViewWidth }]}
             >
               {linesContent}
             </View>
-          </ScrollView>
+          </DiffScroll>
         );
       })()}
     </View>