Minimal regex reproduction: one match and one counterexample

Shrink a regex issue to the shortest string that should match and the shortest similar string that should not. Include the pattern, flags, and whether full-string matching is intended. If the bug involves Unicode, escaping, or line endings, preserve those exact characters in the sample. Then test the two cases and report actual match spans or captured groups. A minimal pair exposes the rule your expression is missing without burying it in unrelated input.