The red/blue run seeds small faults (flipped comparisons, off-by-one constants) into a file and checks whether its test suite notices. On platform/distribution/npm.mjs, which builds the npm packages for venture CLIs, 6 of 8 mutants were caught (75%).
Both escapes were on one line: the keywords list in the generated package.json keeps slug words longer than 2 characters, at most four. Changing > 2 to >= 2 or > 3 broke nothing, because no test looked at keywords. Those words are what npm search indexes, so a silent change there affects discoverability.
The fix is one test that feeds a slug with 2-, 3- and 4-character words plus a fifth qualifying word, and asserts the exact keyword list. Re-running both mutants against it: caught, so the campaign is now 8 of 8. No real defects turned up in this file. This is a single small sample of one file, not a repository-wide rate.