fix(telegram): keep chunk markers outside code fences

When truncate_message appends a (N/M) chunk indicator to a chunk that
had to close an in-progress fenced code block, the marker lands on the
closing fence line (``` \(1/2\) after MarkdownV2 escaping). Telegram
does not treat that as a clean closing fence and rejects the MarkdownV2,
falling back to plain text. Move the indicator onto its own line right
after the closing fence at all three legacy-send call sites.

Fixes #48517

plugins/platforms/telegram/adapter.py

@@ -196,6 +196,24 @@ def _strip_mdv2(text: str) -> str:
     return cleaned
 
 
+_CHUNK_INDICATOR_ON_FENCE_RE = re.compile(
+    r'(?m)^``` (?P<indicator>(?:\\)?\(\d+/\d+(?:\\)?\))$'
+)
+
+
+def _separate_chunk_indicator_from_fence(text: str) -> str:
+    """Move ``(N/M)`` chunk markers off Telegram code-fence lines.
+
+    ``truncate_message()`` appends chunk indicators to the end of a chunk. When
+    the chunk had to close an in-progress fenced code block, that creates a
+    line like ````` \\(1/2\\)`` after MarkdownV2 escaping. Telegram does not
+    treat that as a clean closing fence, so it can reject MarkdownV2 and fall
+    back to plain text. Put the indicator on its own line immediately after the
+    closing fence.
+    """
+    return _CHUNK_INDICATOR_ON_FENCE_RE.sub(r'```\n\g<indicator>', text)
+
+
 # ---------------------------------------------------------------------------
 # Markdown table → Telegram-friendly row groups
 # ---------------------------------------------------------------------------
@@ -2436,7 +2454,9 @@ class TelegramAdapter(BasePlatformAdapter):
                 # MarkdownV2-special parentheses so Telegram doesn't reject the
                 # chunk and fall back to plain text.
                 chunks = [
-                    re.sub(r" \((\d+)/(\d+)\)$", r" \\(\1/\2\\)", chunk)
+                    _separate_chunk_indicator_from_fence(
+                        re.sub(r" \((\d+)/(\d+)\)$", r" \\(\1/\2\\)", chunk)
+                    )
                     for chunk in chunks
                 ]
             
@@ -2910,7 +2930,9 @@ class TelegramAdapter(BasePlatformAdapter):
             if finalize:
                 # Use format_message + parse_mode for the final chunk;
                 # mirror edit_message's main happy-path.
-                formatted = self.format_message(first_chunk)
+                formatted = _separate_chunk_indicator_from_fence(
+                    self.format_message(first_chunk)
+                )
                 try:
                     await self._bot.edit_message_text(
                         chat_id=int(chat_id),
@@ -2971,7 +2993,9 @@ class TelegramAdapter(BasePlatformAdapter):
             for use_markdown in (True, False) if finalize else (False,):
                 try:
                     if use_markdown:
-                        text = self.format_message(chunk)
+                        text = _separate_chunk_indicator_from_fence(
+                            self.format_message(chunk)
+                        )
                     else:
                         # Plain attempt: on finalize the MarkdownV2 attempt
                         # failed, so degrade to clean stripped text, never

tests/gateway/test_telegram_format.py

@@ -178,6 +178,41 @@ class TestFormatMessageCodeBlocks:
         assert r"`\\\\server\\share`" in result
 
 
+@pytest.mark.asyncio
+async def test_legacy_send_keeps_chunk_indicators_outside_fenced_code_lines(adapter):
+    """Chunk markers must not corrupt Telegram MarkdownV2 code fences.
+
+    Telegram treats a closing fenced-code line with trailing text, e.g.
+    ````` (1/2)``, as malformed MarkdownV2. The bot then falls back to plain
+    text, which is the user-visible duplicate/malformed preview symptom.
+    """
+    adapter._bot = MagicMock()
+    adapter._bot.send_message = AsyncMock(
+        side_effect=[SimpleNamespace(message_id=i) for i in range(1, 20)]
+    )
+    adapter._bot.send_chat_action = AsyncMock()
+    object.__setattr__(adapter, "MAX_MESSAGE_LENGTH", 120)
+    adapter._rich_messages_enabled = False
+
+    content = (
+        "Intro before code block\n"
+        "```text\n"
+        + ("~/.hermes/skills/github/hermes-contribution-workflow/SKILL.md\n" * 8)
+        + "```\n"
+        "After."
+    )
+
+    result = await adapter.send("12345", content, metadata={"expect_edits": True})
+
+    assert result.success is True
+    sent_texts = [call.kwargs["text"] for call in adapter._bot.send_message.await_args_list]
+    assert len(sent_texts) > 1
+    for text in sent_texts:
+        for line in text.splitlines():
+            assert not re.match(r"^```\s+\\?\(\d+/\d+\\?\)$", line), text
+            assert not re.match(r"^```\s+\(\d+/\d+\)$", line), text
+
+
 # =========================================================================
 # format_message - bold and italic
 # =========================================================================