fix(telegram): fall back on overflow HTML rejection

nanobot/channels/telegram.py

@@ -1065,7 +1065,7 @@ class TelegramChannel(BaseChannel):
         chunks = _split_telegram_markdown_html_chunks(buf.text, TELEGRAM_HTML_MAX_LEN)
         if len(chunks) <= 1:
             return
-        _, first_html = chunks[0]
+        first_markdown, first_html = chunks[0]
         try:
             await self._call_with_retry(
                 self._app.bot.edit_message_text,
@@ -1073,20 +1073,44 @@ class TelegramChannel(BaseChannel):
                 text=first_html,
                 parse_mode="HTML",
             )
-        except Exception as e:
+        except BadRequest as e:
             if not self._is_not_modified_error(e):
-                self.logger.warning("Stream overflow edit failed: {}", e)
-                raise
-        for _, html in chunks[1:-1]:
-            await self._call_with_retry(
-                self._app.bot.send_message,
-                chat_id=chat_id, text=html, parse_mode="HTML", **thread_kwargs,
-            )
+                self.logger.warning(
+                    "Stream overflow HTML edit failed, falling back to plain text: {}", e
+                )
+                try:
+                    await self._call_with_retry(
+                        self._app.bot.edit_message_text,
+                        chat_id=chat_id, message_id=buf.message_id,
+                        text=first_markdown,
+                    )
+                except Exception as plain_error:
+                    if not self._is_not_modified_error(plain_error):
+                        self.logger.warning("Stream overflow plain edit failed: {}", plain_error)
+                        raise
+        except Exception as e:
+            self.logger.warning("Stream overflow edit failed: {}", e)
+            raise
+
+        async def send_chunk(markdown: str, html: str) -> Any:
+            try:
+                return await self._call_with_retry(
+                    self._app.bot.send_message,
+                    chat_id=chat_id, text=html, parse_mode="HTML", **thread_kwargs,
+                )
+            except BadRequest as e:
+                self.logger.warning(
+                    "Stream overflow HTML send failed, falling back to plain text: {}", e
+                )
+                return await self._call_with_retry(
+                    self._app.bot.send_message,
+                    chat_id=chat_id, text=markdown, **thread_kwargs,
+                )
+
+        for markdown, html in chunks[1:-1]:
+            await send_chunk(markdown, html)
         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,
-        )
+        sent = await send_chunk(markdown_tail, tail_html)
         buf.message_id = sent.message_id
         buf.text = markdown_tail
 

tests/channels/test_telegram_channel.py

@@ -917,6 +917,43 @@ async def test_send_delta_incremental_html_expansion_does_not_overflow() -> None
     assert "<b>" not in buf.text
 
 
+@pytest.mark.asyncio
+async def test_send_delta_incremental_html_parse_failure_falls_back_to_plain() -> None:
+    """Telegram HTML rejections retry overflow chunks as plain text."""
+    from telegram.error import BadRequest
+
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"]),
+        MessageBus(),
+    )
+    channel._app = _FakeApp(lambda: None)
+    channel._app.bot.edit_message_text = AsyncMock(
+        side_effect=[BadRequest("Can't parse entities"), None]
+    )
+    channel._app.bot.send_message = AsyncMock(
+        side_effect=[BadRequest("Can't parse entities"), SimpleNamespace(message_id=99)]
+    )
+
+    first_chunk = f"**{'x' * 3900}**\n"
+    tail = "**tail** " * 50
+    channel._stream_bufs["123"] = _StreamBuf(
+        text=first_chunk + tail, message_id=7, last_edit=0.0, stream_id="s:0"
+    )
+
+    await channel.send_delta("123", "y", stream_id="s:0")
+
+    edit_calls = channel._app.bot.edit_message_text.call_args_list
+    assert edit_calls[0].kwargs["parse_mode"] == "HTML"
+    assert edit_calls[1].kwargs["text"] == first_chunk.rstrip()
+    assert "parse_mode" not in edit_calls[1].kwargs
+
+    send_calls = channel._app.bot.send_message.call_args_list
+    assert send_calls[0].kwargs["parse_mode"] == "HTML"
+    assert send_calls[1].kwargs["text"] == tail + "y"
+    assert "parse_mode" not in send_calls[1].kwargs
+    assert channel._stream_bufs["123"].text == tail + "y"
+
+
 @pytest.mark.asyncio
 async def test_send_delta_initial_send_keeps_message_in_thread() -> None:
     channel = TelegramChannel(