fix: Leerzeilenfolgen innerhalb von Codeblöcken erhalten (QA2-06)

render_chapter reduzierte mehrfache Leerzeilen im gesamten Kapiteltext,
auch innerhalb von Codeblöcken (z. B. zwei Leerzeilen zwischen
Python-Funktionen nach PEP 8). Im Python-Beispielbuch waren 54 von 746
Listings nicht mehr zeichengetreu. Die Normalisierung gilt jetzt nur
außerhalb von Fences.

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

epub2md/html_converter.py

@@ -152,6 +152,26 @@ def indent_block(text: str, first: str, rest: str) -> str:
     return "\n".join(out)
 
 
+def _collapse_blank_lines(text: str) -> str:
+    """Reduce runs of blank lines to one, except inside fenced code blocks (also indented/quoted ones)."""
+    out: list[str] = []
+    fence = ""
+    for line in text.split("\n"):
+        bare = re.sub(r"^[ \t]*(?:>[ \t]?)*[ \t]*", "", line)
+        if fence:
+            if bare.rstrip() and set(bare.rstrip()) == {fence[0]} and len(bare.rstrip()) >= len(fence):
+                fence = ""
+            out.append(line)
+            continue
+        m = re.match(r"(`{3,}|~{3,})", bare)
+        if m:
+            fence = m.group(1)
+        elif not line.strip() and out and not out[-1].strip():
+            continue
+        out.append(line)
+    return "\n".join(out)
+
+
 _BLOCK_SYNTAX = ("```", "~~~", "|", "<table", "- ", "> ", "#", "$$", "\\[", "* * *")
 
 
@@ -251,7 +271,7 @@ class Renderer:
         blocks.extend(self.render_items(ch.items))
         blocks.extend(self._chapter_note_definitions())
         text = "\n\n".join(b for b in blocks if b.strip())
-        return re.sub(r"\n{3,}", "\n\n", text).strip() + "\n"
+        return _collapse_blank_lines(text).strip() + "\n"
 
     def render_items(self, items: Sequence[tuple[str | None, Any]]) -> list[str]:
         blocks: list[str] = []

tests/test_qa_regressions.py

@@ -98,3 +98,12 @@ def test_inline_svg_inside_html_table_is_html_img(convert):
     assert "![" not in table, table
     assert re.search(r'<img src="\.\./media/images/\d{4}-c-svg\.svg" alt="Kreis"/>', table), table
     assert run.report["output_link_check"]["broken_count"] == 0
+
+
+def test_multiple_blank_lines_inside_code_are_kept(convert):
+    """QA2-06: runs of blank lines inside code blocks were collapsed to one (PEP 8: two between functions)."""
+    code = "def f():\n    pass\n\n\nclass K:\n    pass\n\n\n\nx = 1"
+    body = f"<h1>K</h1><p>Vorher</p><pre>{code}</pre><p>Nachher</p>"
+    text = convert(Book(docs=[Doc("c.xhtml", body)])).chapter("001")
+    assert f"```python\n{code}\n```" in text, text
+    assert "\n\n\n" not in text.replace(code, "")  # outside code blank lines are still normalized