fix(visual_report): ignore fenced headings in TOC extraction

Strip fenced code blocks before extracting visual-report headings so heading-looking lines inside code fences do not desync TOC anchors. Add regression coverage for backtick and tilde fences while preserving normal heading extraction.

tests/test_visual_report_toc_code_fence.py

@@ -0,0 +1,28 @@
+"""TOC heading extraction must ignore headings inside code fences.
+
+A "## ..." comment inside a ``` or ~~~ block is not rendered as an <h2>, but
+_extract_headings counted it, so _apply_heading_ids (which zips TOC headings
+against rendered <h2>/<h3> by position) gave later sections the wrong anchor
+id and the trailing TOC link went dead.
+"""
+import pytest
+
+pytest.importorskip("bs4")
+
+from src.visual_report import _extract_headings
+
+
+def test_backtick_fenced_heading_is_ignored():
+    md = "## Intro\n\n```bash\n## not a heading\n```\n\n## Conclusion"
+    assert [h["text"] for h in _extract_headings(md)] == ["Intro", "Conclusion"]
+
+
+def test_tilde_fenced_heading_is_ignored():
+    md = "## A\n\n~~~\n## fake\n~~~\n\n## B"
+    assert [h["text"] for h in _extract_headings(md)] == ["A", "B"]
+
+
+def test_normal_headings_unaffected():
+    md = "## One\n\nsome text\n\n### Two"
+    out = [(h["level"], h["text"]) for h in _extract_headings(md)]
+    assert out == [(2, "One"), (3, "Two")]