fix(channels): avoid blank boundary chunks

Signed-off-by: chengyongru <2755839590@qq.com>

nanobot/utils/helpers.py

@@ -636,7 +636,8 @@ def split_message(content: str, max_len: int = 2000) -> list[str]:
     chunks: list[str] = []
     while content:
         if len(content) <= max_len:
-            chunks.append(content)
+            if content.strip():
+                chunks.append(content)
             break
         cut = content[:max_len]
         # Consume only the newline itself so indentation starts the next chunk.
@@ -656,6 +657,14 @@ def split_message(content: str, max_len: int = 2000) -> list[str]:
 
         chunks.append(content[:max_len])
         content = content[max_len:]
+        # A delimiter can sit immediately after the hard-break boundary. Keep
+        # ordinary space trimming, but consume only the newline so indentation
+        # on the following line is preserved.
+        content = content.lstrip(" \t")
+        if content.startswith("\r\n"):
+            content = content[2:]
+        elif content.startswith("\n"):
+            content = content[1:]
     return chunks
 
 

tests/utils/test_helpers.py

@@ -29,6 +29,23 @@ def test_split_message_preserves_indentation_across_hard_break():
     assert split_message(content, max_len=8) == ["head", "    abcd", "efghij"]
 
 
+def test_split_message_preserves_indentation_when_newline_is_at_hard_break():
+    content = "abcdefgh\n    code"
+
+    assert split_message(content, max_len=8) == ["abcdefgh", "    code"]
+    assert split_message(content.replace("\n", "\r\n"), max_len=8) == [
+        "abcdefgh",
+        "    code",
+    ]
+
+
+def test_split_message_drops_whitespace_only_tail_after_hard_break():
+    prefix = "abcdefgh"
+
+    assert split_message(prefix + "\n", max_len=8) == [prefix]
+    assert split_message(prefix + " ", max_len=8) == [prefix]
+
+
 def test_split_message_nonpositive_maxlen_returns_unsplit():
     content = "alpha beta gamma delta"