PR #2428's iterative _protectPipes regex introduced two issues we caught during stage assembly:
1. The negated character classes [^)\]}'>] added `'` as a stop character. That breaks cells containing string-literal pipes like `('a'|'b')` (Python type-union examples) — they would still mis-split. Dropped the apostrophe-stop.
2. The literal `}` inside the regex character classes confused the brace-counting extractFunc driver in tests/test_renderer_js_behaviour.py, breaking all 45 existing node-driven renderer tests. Rewrote both brace literals as hex escapes (\\x7b and \\x7d) — semantically identical at the regex-engine level but the JS source carries no bare brace glyph.
Also added tests/test_issue2428_table_pipe_protection.py with 9 regression tests covering single-pipe, multi-pipe-in-brackets, apostrophes-with-pipes, and the KaTeX \$...\$ guard.
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