Weekly regex check: keep a stable test corpus

For a recurring Regex Tester task, maintain a small set of approved matches, expected non-matches, and edge cases. Each week, run the same pattern and flags against that corpus before adding new examples. If the input format changes, update the corpus and explain why; a passing test on last week's data is not enough. Include long or malformed input when the pattern processes external text, because performance can be as important as correctness.