fix(telegram): advance markdown split on long single-line fences

When a fenced code body has no interior newlines, the splitter cut at the
opening fence line and re-emitted the same content forever. Prefer breaks
inside the body after the fence so long JSON/minified blocks still split.

nanobot/channels/telegram/runtime.py

@@ -90,18 +90,27 @@ def _split_telegram_markdown(content: str, max_len: int) -> list[str]:
                 min_code_pos = len(fence)
                 if content.startswith(fence + "\n"):
                     min_code_pos += 1
-                if pos < min_code_pos and min_code_pos + len(closing) > max_len:
-                    chunks.append(content[:max_len])
-                    content = content[max_len:].lstrip()
-                    continue
-                if pos + len(closing) > max_len:
+                # When the only break in range is the opening fence newline,
+                # cutting there re-emits the same fence and never advances.
+                if pos < min_code_pos:
+                    if min_code_pos + len(closing) > max_len:
+                        chunks.append(content[:max_len])
+                        content = content[max_len:].lstrip()
+                        continue
+                    budget = max_len - len(closing)
+                    recut = content[:budget]
+                    adjusted = recut.rfind("\n", min_code_pos)
+                    if adjusted < min_code_pos:
+                        adjusted = recut.rfind(" ", min_code_pos)
+                    pos = adjusted if adjusted >= min_code_pos else budget
+                elif pos + len(closing) > max_len:
                     budget = max_len - len(closing)
                     if budget > 0:
                         recut = content[:budget]
-                        adjusted = recut.rfind("\n")
-                        if adjusted <= 0:
-                            adjusted = recut.rfind(" ")
-                        pos = adjusted if adjusted > 0 else budget
+                        adjusted = recut.rfind("\n", min_code_pos)
+                        if adjusted < min_code_pos:
+                            adjusted = recut.rfind(" ", min_code_pos)
+                        pos = adjusted if adjusted >= min_code_pos else budget
                     else:
                         closing = "```"
                         pos = max_len - len(closing)

nanobot/channels/telegram/tests/test_telegram_channel.py

@@ -15,6 +15,7 @@ from nanobot.bus.events import OutboundMessage
 from nanobot.bus.outbound_events import ProgressEvent
 from nanobot.bus.queue import MessageBus
 from nanobot.channels.telegram.runtime import (
+    TELEGRAM_MAX_MESSAGE_LEN,
     TELEGRAM_REPLY_CONTEXT_MAX_LEN,
     TelegramChannel,
     TelegramConfig,
@@ -243,6 +244,30 @@ def test_split_telegram_markdown_leading_whitespace_before_fence() -> None:
     _assert_code_blocks_render_balanced(chunks)
 
 
+def test_split_telegram_markdown_long_single_line_code_body() -> None:
+    """Long fence bodies with no interior newlines must still advance."""
+    body = "a" * 4500
+    content = f"```\n{body}\n```"
+
+    chunks = _split_telegram_markdown(content, TELEGRAM_MAX_MESSAGE_LEN)
+
+    assert len(chunks) > 1
+    assert all(len(chunk) <= TELEGRAM_MAX_MESSAGE_LEN for chunk in chunks)
+    assert chunks[0].startswith("```\n")
+    assert chunks[0].endswith("\n```")
+    assert chunks[1].startswith("```\n")
+    reassembled = []
+    for chunk in chunks:
+        part = chunk.split("\n", 1)[1]
+        if part.endswith("\n```"):
+            part = part[:-4]
+        elif part.endswith("```"):
+            part = part[:-3]
+        reassembled.append(part)
+    assert "".join(reassembled) == body
+    _assert_code_blocks_render_balanced(chunks)
+
+
 @pytest.mark.asyncio
 async def test_start_creates_separate_pools_with_proxy(monkeypatch) -> None:
     _FakeHTTPXRequest.clear()