The suite was the only file in tests/docker using node:test. The repository's
dominant convention, in 229 of 327 test files including the sibling
gateguard-effectiveness suite, is a local test() helper that counts passes and
sets process.exitCode, which is what tests/run-all.js reads.
Adopt that helper verbatim, along with the sibling's tempDir wrapper so the
scenario fixtures resolve symlinked temp paths. Assertions are unchanged.