[xiehuanyi]

Reusing a global or sticky RegExp makes .match() depend on its previous lastIndex. A valid positive assertion can fail, and a negated assertion can silently pass for the same matching input after an earlier match.

Evaluate stateful expressions from index zero and restore the caller's index before reporting the assertion result. Ordinary expressions are evaluated without mutation, including frozen regexps. Add regressions for repeated matches, existing index preservation, negated false positives, and frozen ordinary expressions.

Validation:

• Two added regressions fail on unchanged main; the frozen-regexp control passes before and after.
• npm run build and npm run lint pass.
• Node suite: 515 passing. Chromium suite using the local Chrome executable: 514 passing.
• git diff --check passes.

Discovery and implementation: automated OpenAI gpt-6.1-sol source review, xhigh reasoning.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.