feat: import Chinese-localized Buzz source snapshot

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

mobile/lib/shared/emoji/emoji_only.dart

@@ -0,0 +1,87 @@
+/// Detection and sizing for messages whose entire body is emoji, ported from
+/// desktop's `isEmojiOnlyMessage` (`desktop/src/shared/lib/emojiOnly.ts`) and
+/// the `emojiOnly` branch of `MessageRow.tsx`.
+library;
+
+import 'package:characters/characters.dart';
+
+import '../custom_emoji/custom_emoji.dart';
+
+/// Body size for an emoji-only message. Desktop steps `text-sm` (14px) up to
+/// `text-4xl`; mobile body text is the same 14px, so the same 36px lands the
+/// same jump.
+const double kEmojiOnlyFontSize = 36.0;
+
+/// Line height for an emoji-only body — desktop's `leading-tight`. Emoji have
+/// generous internal leading already, so normal line spacing leaves a gap that
+/// reads as a blank row.
+const double kEmojiOnlyHeight = 1.25;
+
+/// Inline custom-emoji size inside an emoji-only message. Desktop sizes these
+/// at `1.45em` of the surrounding text.
+const double kEmojiOnlyCustomEmojiSize = kEmojiOnlyFontSize * 1.45;
+
+/// Anything with `Extended_Pictographic` in it is emoji enough. Keycaps and
+/// digit-based sequences don't match — those are covered by the dataset's own
+/// native set instead, exactly as desktop does it.
+final RegExp _pictographic = RegExp(
+  r'\p{Extended_Pictographic}',
+  unicode: true,
+);
+
+/// Whether [content] is nothing but emoji — native glyphs, known custom
+/// `:shortcode:`s, and whitespace, with at least one emoji present.
+///
+/// [nativeEmoji] is the dataset's glyph set — read `nativeEmojiGlyphsProvider`.
+/// Passing an empty set still gives correct results for ordinary emoji, since
+/// the pictographic check stands on its own; only glyphs with no pictographic
+/// code point of their own (keycaps like 1️⃣) need the set.
+bool isEmojiOnlyMessage(
+  String content, {
+  required Set<String> nativeEmoji,
+  List<CustomEmoji> customEmoji = const [],
+}) {
+  final trimmed = content.trim();
+  if (trimmed.isEmpty) return false;
+
+  final shortcodes = {
+    for (final emoji in customEmoji) emoji.shortcode.toLowerCase(),
+  };
+  var sawEmoji = false;
+
+  // Grapheme clusters, so a ZWJ family or a flag pair is one unit. Desktop
+  // hand-rolls this scan; Dart's `characters` already segments correctly.
+  final iterator = trimmed.characters.iterator;
+  final clusters = <String>[];
+  while (iterator.moveNext()) {
+    clusters.add(iterator.current);
+  }
+
+  var index = 0;
+  while (index < clusters.length) {
+    final cluster = clusters[index];
+
+    if (cluster.trim().isEmpty) {
+      index += 1;
+      continue;
+    }
+
+    if (cluster == ':') {
+      final end = clusters.indexOf(':', index + 1);
+      if (end <= index + 1) return false;
+      final shortcode = clusters.sublist(index + 1, end).join().toLowerCase();
+      if (!shortcodes.contains(shortcode)) return false;
+      sawEmoji = true;
+      index = end + 1;
+      continue;
+    }
+
+    if (!nativeEmoji.contains(cluster) && !_pictographic.hasMatch(cluster)) {
+      return false;
+    }
+    sawEmoji = true;
+    index += 1;
+  }
+
+  return sawEmoji;
+}