fix: Zeilen aus nur - oder = als Text maskieren (QA2-08)

Ein Absatz "---" wurde zur Trennlinie, "===" bzw. "---" nach einem
Zeilenumbruch machte die vorige Zeile zur Setext-Überschrift. Solche
Zeilen erhalten jetzt einen Backslash.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

epub2md/html_converter.py

@@ -116,6 +116,9 @@ def escape_line_starts(text: str) -> str:
             token = m.group(2)
             pos = m.start(2) + (len(token) - 1 if token[0].isdigit() else 0)
             line = line[:pos] + "\\" + line[pos:]
+        elif re.fullmatch(r"\s*(-+|=+)\s*", line):  # thematic break / setext underline
+            pos = len(line) - len(line.lstrip())
+            line = line[:pos] + "\\" + line[pos:]
         out.append(line)
     return "\n".join(out)
 

tests/test_qa_regressions.py

@@ -109,6 +109,15 @@ def test_multiple_blank_lines_inside_code_are_kept(convert):
     assert "\n\n\n" not in text.replace(code, "")  # outside code blank lines are still normalized
 
 
+def test_dash_and_equals_lines_stay_text(convert):
+    """QA2-08: a paragraph '---' became a thematic break, '===' after a line break a setext heading."""
+    body = "<h1>K</h1><p>---</p><p>Zeile<br/>===</p><p>Text<br/>-----</p>"
+    text = convert(Book(docs=[Doc("c.xhtml", body)])).chapter("001")
+    assert "\n\\---\n" in text, text
+    assert "Zeile\\\n\\===" in text, text
+    assert "Text\\\n\\-----" in text, text
+
+
 def _simple() -> Book:
     return Book(docs=[Doc("c.xhtml", "<h1>K</h1><p>Text.</p>")])