feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

mobile/lib/shared/widgets/keyboard_dismiss_on_drag.dart

@@ -0,0 +1,107 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_hooks/flutter_hooks.dart';
+
+/// How far a finger must travel downward before the keyboard is dismissed.
+///
+/// Large enough that reading-speed scrolling never trips it, small enough that
+/// a deliberate "push it away" swipe feels immediate.
+const keyboardDismissDragThreshold = 48.0;
+
+/// Dismiss the software keyboard when the user deliberately drags downward.
+///
+/// Flutter only offers `ScrollViewKeyboardDismissBehavior.manual` and `.onDrag`
+/// — and `.onDrag` fires the instant a drag begins, so a one-pixel scroll to
+/// re-read a message would tear the keyboard away. Neither is available on
+/// `ScrollablePositionedList` regardless, which is what both message lists use.
+///
+/// So: accumulate raw finger travel and only unfocus once a downward drag
+/// clears [keyboardDismissDragThreshold]. Any upward movement resets the
+/// accumulator, so a scroll that wanders up and down never adds up to a
+/// dismissal.
+///
+/// This tracks the *finger*, not the scroll direction, so it behaves the same
+/// in the reversed channel timeline and the top-anchored thread list. It is not
+/// interactive dismissal — the keyboard animates away on the OS's own curve
+/// rather than following the finger, which Flutter can't do without a native
+/// plugin (iOS `UIScrollView.keyboardDismissMode`, Android
+/// `WindowInsetsAnimationController`).
+class KeyboardDismissOnDrag extends HookWidget {
+  final Widget child;
+  final VoidCallback? onUserScrollStart;
+
+  const KeyboardDismissOnDrag({
+    super.key,
+    this.onUserScrollStart,
+    required this.child,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    // A ref, not state: accumulating travel must never trigger a rebuild of
+    // the message list this wraps.
+    final downwardTravel = useRef(0.0);
+
+    bool handle(ScrollNotification notification) {
+      if (notification is ScrollStartNotification) {
+        if (notification.dragDetails != null) onUserScrollStart?.call();
+        downwardTravel.value = 0;
+        return false;
+      }
+      if (notification is ScrollEndNotification) {
+        downwardTravel.value = 0;
+        return false;
+      }
+
+      // Overscroll counts as much as ordinary scrolling. You focus the composer
+      // at the resting end of the list far more often than not, and there a
+      // downward drag moves the position nowhere — it is pure overscroll, and
+      // reports `OverscrollNotification` instead. Listening only for
+      // `ScrollUpdateNotification` meant the most common dismissal gesture in
+      // both lists produced no notification this saw at all.
+      final DragUpdateDetails? drag;
+      if (notification is ScrollUpdateNotification) {
+        drag = notification.dragDetails;
+      } else if (notification is OverscrollNotification) {
+        drag = notification.dragDetails;
+      } else {
+        return false;
+      }
+
+      // Null during a momentum fling — only a finger still on the glass should
+      // dismiss, so a fling that coasts downward leaves the keyboard up.
+      if (drag == null) {
+        downwardTravel.value = 0;
+        return false;
+      }
+
+      final dy = drag.delta.dy;
+      if (dy <= 0) {
+        downwardTravel.value = 0;
+        return false;
+      }
+
+      downwardTravel.value += dy;
+      if (downwardTravel.value < keyboardDismissDragThreshold) return false;
+      downwardTravel.value = 0;
+      dismissKeyboard(context);
+      return false;
+    }
+
+    return NotificationListener<ScrollNotification>(
+      onNotification: handle,
+      child: child,
+    );
+  }
+}
+
+/// Drop focus so the OS retracts the keyboard. No-op when nothing is focused
+/// or the keyboard is already down, so callers can fire it freely.
+void dismissKeyboard(BuildContext context) {
+  // Read the view's own insets, not MediaQuery's. `Scaffold` strips the bottom
+  // view inset from its body while `resizeToAvoidBottomInset` is on — it has
+  // already resized to account for it — so a MediaQuery read from anywhere
+  // inside the body reports 0 whether the keyboard is up or not, which made
+  // this gate a permanent no-op for both message lists and the compose bar.
+  if (View.of(context).viewInsets.bottom <= 0) return;
+  FocusManager.instance.primaryFocus?.unfocus();
+}