update fence closure to match common mark spec

Signed-off-by: Jordan Dubrick <jdubrick@redhat.com>

Author: Jdubrick

src/utils/markdown_repair.py

@@ -86,7 +86,11 @@ def close_open_markdown(text: str) -> str:
             in_code_fence = True
             fence_char = char
             fence_len = len(matched_group)
-        elif char == fence_char and len(matched_group) >= fence_len:
+        elif (
+            char == fence_char
+            and len(matched_group) >= fence_len
+            and line[fence_match.end() :].strip(" \t") == ""
+        ):
             in_code_fence = False
             fence_char = ""
             fence_len = 0

tests/unit/utils/test_markdown_repair.py

@@ -60,6 +60,18 @@ def test_shorter_fence_inside_longer_fence_not_closer(self) -> None:
         result = close_open_markdown(text)
         assert result == "\n````"
 
+    def test_fence_with_trailing_text_not_closer(self) -> None:
+        """A fence marker with trailing non-whitespace inside a fence is content."""
+        text = "```python\nprint('x')\n```not a closer"
+        result = close_open_markdown(text)
+        assert result == "\n```"
+
+    def test_fence_with_trailing_whitespace_is_closer(self) -> None:
+        """A fence marker with only trailing whitespace is a valid closer."""
+        text = "```python\nprint('x')\n```   "
+        result = close_open_markdown(text)
+        assert result == ""
+
 
 class TestCloseOpenMarkdownHtmlTags:
     """Tests for closing unclosed HTML block tags."""