Validate enlarged emoji-only messages on iOS

Signed-off-by: Tom Brow <tomb@block.xyz>

mobile/test/visual/heart_sim_app.dart

@@ -43,7 +43,7 @@ void main() => runApp(
                 _message('Ελληνικά · Кириллица · Tiếng Việt'),
                 const SizedBox(height: 16),
                 const Text('Emoji-only message'),
-                _message('❤️ ⚠️'),
+                _message('❤️ ⚠️', scaleEmojiOnly: true),
               ],
             ),
           ),
@@ -67,7 +67,9 @@ Widget _reactions(bool selected) => ReactionRow(
   onToggle: (_) {},
 );
 
-Widget _message(String content) => MessageContent(
-  content: content,
-  channelNames: const {'general': 'general'},
-);
+Widget _message(String content, {bool scaleEmojiOnly = false}) =>
+    MessageContent(
+      content: content,
+      scaleEmojiOnly: scaleEmojiOnly,
+      channelNames: const {'general': 'general'},
+    );

mobile/test/visual/verify_heart_screenshots.py

@@ -42,7 +42,7 @@ def main():
         "text-presentation message heart": (550, 980, 620, 1035),
         "bold message heart": (170, 1040, 220, 1090),
         "italic message heart": (430, 1040, 490, 1090),
-        "emoji-only message": (65, 1490, 125, 1545),
+        "emoji-only message": (65, 1490, 200, 1650),
     }
     warnings = {
         "selected warning reaction": (260, 522, 325, 606),
@@ -52,13 +52,22 @@ def main():
         "text-presentation message warning": (430, 1090, 490, 1150),
         "bold message warning": (230, 1040, 290, 1090),
         "italic message warning": (490, 1040, 550, 1090),
-        "emoji-only warning": (130, 1490, 190, 1550),
+        "emoji-only warning": (205, 1490, 335, 1650),
     }
     for cases, predicate in ((regions, is_red), (warnings, is_yellow)):
         for name, box in cases.items():
             assert not color_pixels(before, box, predicate), f"{name}: original must reproduce monochrome glyph"
             pixels = color_pixels(after, box, predicate)
             assert len(pixels) > 500, f"{name}: expected native color emoji"
+            if "emoji-only" in name:
+                # Production uses a separate 36sp path. Reject a fixture that
+                # accidentally renders normal-sized inline emoji or clips it.
+                left, right = min(x for x, _ in pixels), max(x for x, _ in pixels)
+                top, bottom = min(y for _, y in pixels), max(y for _, y in pixels)
+                assert len(pixels) > 4500, f"{name}: expected enlarged emoji"
+                assert 90 <= right - left <= 110 and 90 <= bottom - top <= 110
+                assert box[0] < left < right < box[2] - 1
+                assert box[1] < top < bottom < box[3] - 1
             if "reaction" in name:
                 center = (min(y for _, y in pixels) + max(y for _, y in pixels)) / 2
                 pill_center = (box[1] + box[3] - 1) / 2