fix(telegram): bound streamed HTML overflow chunks

nanobot/channels/telegram.py

@@ -286,15 +286,17 @@ def _markdown_to_telegram_html(text: str) -> str:
     return text
 
 
-def _split_telegram_markdown_html(content: str, max_html_len: int) -> list[str]:
-    """Split raw Telegram Markdown and return HTML chunks within Telegram's limit."""
-    chunks: list[str] = []
+def _split_telegram_markdown_html_chunks(
+    content: str, max_html_len: int,
+) -> list[tuple[str, str]]:
+    """Return raw Markdown and rendered HTML chunk pairs within Telegram's limit."""
+    chunks: list[tuple[str, str]] = []
     pending = _split_telegram_markdown(content, TELEGRAM_MAX_MESSAGE_LEN)
     while pending:
         chunk = pending.pop(0)
         html = _markdown_to_telegram_html(chunk)
         if len(html) <= max_html_len:
-            chunks.append(html)
+            chunks.append((chunk, html))
             continue
 
         # Markdown can expand when rendered as HTML (tags/entities). Re-split
@@ -302,16 +304,19 @@ def _split_telegram_markdown_html(content: str, max_html_len: int) -> list[str]:
         next_limit = max(1, int(len(chunk) * max_html_len / len(html)) - 8)
         next_limit = min(next_limit, len(chunk) - 1)
         if next_limit <= 0:
-            chunks.extend(split_message(html, max_html_len))
-            continue
+            raise ValueError("A rendered Telegram HTML token exceeds the message limit")
         parts = _split_telegram_markdown(chunk, next_limit)
         if len(parts) == 1 and parts[0] == chunk:
-            chunks.extend(split_message(html, max_html_len))
-            continue
+            raise ValueError("Unable to split Telegram Markdown within the HTML limit")
         pending = parts + pending
     return chunks
 
 
+def _split_telegram_markdown_html(content: str, max_html_len: int) -> list[str]:
+    """Split raw Telegram Markdown and return HTML chunks within Telegram's limit."""
+    return [html for _, html in _split_telegram_markdown_html_chunks(content, max_html_len)]
+
+
 _SEND_MAX_RETRIES = 3
 _SEND_RETRY_BASE_DELAY = 0.5  # seconds, doubled each retry
 _STREAM_EDIT_INTERVAL_DEFAULT = 0.6  # min seconds between edit_message_text calls
@@ -1057,28 +1062,27 @@ class TelegramChannel(BaseChannel):
         intermediate chunks as standalone messages, then opens a new message
         for the tail so subsequent deltas continue streaming into it.
         """
-        chunks = _split_telegram_markdown(buf.text, TELEGRAM_MAX_MESSAGE_LEN)
+        chunks = _split_telegram_markdown_html_chunks(buf.text, TELEGRAM_HTML_MAX_LEN)
         if len(chunks) <= 1:
             return
-        html_chunks = [_markdown_to_telegram_html(chunk) for chunk in chunks]
+        _, first_html = chunks[0]
         try:
             await self._call_with_retry(
                 self._app.bot.edit_message_text,
                 chat_id=chat_id, message_id=buf.message_id,
-                text=html_chunks[0],
+                text=first_html,
                 parse_mode="HTML",
             )
         except Exception as e:
             if not self._is_not_modified_error(e):
                 self.logger.warning("Stream overflow edit failed: {}", e)
                 raise
-        for chunk in html_chunks[1:-1]:
+        for _, html in chunks[1:-1]:
             await self._call_with_retry(
                 self._app.bot.send_message,
-                chat_id=chat_id, text=chunk, parse_mode="HTML", **thread_kwargs,
+                chat_id=chat_id, text=html, parse_mode="HTML", **thread_kwargs,
             )
-        markdown_tail = chunks[-1]
-        tail_html = html_chunks[-1]
+        markdown_tail, tail_html = chunks[-1]
         sent = await self._call_with_retry(
             self._app.bot.send_message,
             chat_id=chat_id, text=tail_html, parse_mode="HTML", **thread_kwargs,

tests/channels/test_telegram_channel.py

@@ -851,7 +851,42 @@ async def test_send_delta_incremental_edit_splits_oversized_buffer() -> None:
     """Mid-stream overflow: once buf.text exceeds Telegram's limit, split into
     chunks, edit the current message with the first chunk, and re-anchor the
     buffer to a new message for the tail so further deltas keep streaming."""
-    from nanobot.channels.telegram import TELEGRAM_MAX_MESSAGE_LEN
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"]),
+        MessageBus(),
+    )
+    channel._app = _FakeApp(lambda: None)
+    channel._app.bot.edit_message_text = AsyncMock()
+    channel._app.bot.send_message = AsyncMock(return_value=SimpleNamespace(message_id=99))
+
+    first_chunk = f"**{'x' * 3900}**\n"
+    tail = "**tail** " * 50
+    oversized = first_chunk + tail
+    channel._stream_bufs["123"] = _StreamBuf(
+        text=oversized, message_id=7, last_edit=0.0, stream_id="s:0"
+    )
+
+    await channel.send_delta("123", "y", stream_id="s:0")
+
+    channel._app.bot.edit_message_text.assert_called_once()
+    edit_kwargs = channel._app.bot.edit_message_text.call_args.kwargs
+    assert edit_kwargs["text"] == _markdown_to_telegram_html(first_chunk.rstrip())
+    assert edit_kwargs["parse_mode"] == "HTML"
+
+    channel._app.bot.send_message.assert_called_once()
+    send_kwargs = channel._app.bot.send_message.call_args.kwargs
+    assert send_kwargs["parse_mode"] == "HTML"
+    buf = channel._stream_bufs["123"]
+    assert buf.message_id == 99
+    assert buf.text == tail + "y"
+    assert send_kwargs["text"] == _markdown_to_telegram_html(buf.text)
+    assert buf.last_edit > 0.0
+
+
+@pytest.mark.asyncio
+async def test_send_delta_incremental_html_expansion_does_not_overflow() -> None:
+    """Mid-stream HTML chunks stay within Telegram's rendered payload limit."""
+    from nanobot.channels.telegram import TELEGRAM_HTML_MAX_LEN
 
     channel = TelegramChannel(
         TelegramConfig(enabled=True, token="123:abc", allow_from=["*"]),
@@ -861,22 +896,25 @@ async def test_send_delta_incremental_edit_splits_oversized_buffer() -> None:
     channel._app.bot.edit_message_text = AsyncMock()
     channel._app.bot.send_message = AsyncMock(return_value=SimpleNamespace(message_id=99))
 
-    oversized = "x" * (TELEGRAM_MAX_MESSAGE_LEN + 500)
+    oversized = "**bold** " * 501
+    assert len(_markdown_to_telegram_html(oversized)) > TELEGRAM_HTML_MAX_LEN
     channel._stream_bufs["123"] = _StreamBuf(
         text=oversized, message_id=7, last_edit=0.0, stream_id="s:0"
     )
 
     await channel.send_delta("123", "y", stream_id="s:0")
 
-    channel._app.bot.edit_message_text.assert_called_once()
-    edit_text = channel._app.bot.edit_message_text.call_args.kwargs.get("text", "")
-    assert len(edit_text) <= TELEGRAM_MAX_MESSAGE_LEN
+    payloads = [
+        channel._app.bot.edit_message_text.call_args.kwargs,
+        *[call.kwargs for call in channel._app.bot.send_message.call_args_list],
+    ]
+    assert len(payloads) > 1
+    assert all(payload["parse_mode"] == "HTML" for payload in payloads)
+    assert all(len(payload["text"]) <= TELEGRAM_HTML_MAX_LEN for payload in payloads)
 
-    channel._app.bot.send_message.assert_called_once()
     buf = channel._stream_bufs["123"]
-    assert buf.message_id == 99
-    assert len(buf.text) <= TELEGRAM_MAX_MESSAGE_LEN
-    assert buf.last_edit > 0.0
+    assert payloads[-1]["text"] == _markdown_to_telegram_html(buf.text)
+    assert "<b>" not in buf.text
 
 
 @pytest.mark.asyncio