fix(gateway): support Telegram MarkdownV2 expandable blockquotes

gateway/platforms/telegram.py

@@ -1916,9 +1916,20 @@ class TelegramAdapter(BasePlatformAdapter):
         )
 
         # 9) Convert blockquotes: > at line start → protect > from escaping
+        #    Handle both regular blockquotes (> text) and expandable blockquotes
+        #    (Telegram MarkdownV2: **> for expandable start, || to end the quote)
+        def _convert_blockquote(m):
+            prefix = m.group(1)  # >, >>, >>>, **>, or **>> etc.
+            content = m.group(2)
+            # Check if content ends with || (expandable blockquote end marker)
+            # In this case, preserve the trailing || unescaped for Telegram
+            if prefix.startswith('**') and content.endswith('||'):
+                return _ph(f'{prefix} {_escape_mdv2(content[:-2])}||')
+            return _ph(f'{prefix} {_escape_mdv2(content)}')
+
         text = re.sub(
-            r'^(>{1,3}) (.+)$',
+            r'^((?:\*\*)?>{1,3}) (.+)$',
-            lambda m: _ph(m.group(1) + ' ' + _escape_mdv2(m.group(2))),
+            _convert_blockquote,
             text,
             flags=re.MULTILINE,
         )

tests/gateway/test_telegram_format.py

@@ -408,6 +408,27 @@ class TestFormatMessageBlockquote:
         result = adapter.format_message("5 > 3")
         assert "\\>" in result
 
+    def test_expandable_blockquote(self, adapter):
+        """Expandable blockquote prefix **> and trailing || must NOT be escaped."""
+        result = adapter.format_message("**> Hidden content||")
+        assert "**>" in result
+        assert "||" in result
+        assert "\\*" not in result  # asterisks in prefix must not be escaped
+        assert "\\>" not in result  # > in prefix must not be escaped
+
+    def test_single_asterisk_gt_not_blockquote(self, adapter):
+        """Single asterisk before > should not be treated as blockquote prefix."""
+        result = adapter.format_message("*> not a quote")
+        assert "\\*" in result
+        assert "\\>" in result
+
+    def test_regular_blockquote_with_pipes_escaped(self, adapter):
+        """Regular blockquote ending with || should escape the pipes."""
+        result = adapter.format_message("> not expandable||")
+        assert "> not expandable" in result
+        assert "\\|" in result
+        assert "\\>" not in result
+
 
 # =========================================================================
 # format_message - mixed/complex