gauntlet

Gauntlet gates

These gates sit next to the CRAP gate (crap-gate skill). They score only the functions that your change touched, since the merge-base with origin/main. Locally they only report. In CI each gate has a mode, from a repo variable: DRY_MODE and MUTATION_MODE. Unset or any other value is warn mode, where the job only reports. With block:

• Quality / DRY fails, and so does Required, while a new duplicate that no marker accepts remains.
• Quality / Mutation fails while a survivor that no marker accepts remains. Required does not wait for it, in either mode.

A tool error, a timeout, a baseline failure, an error row, a mutant that did not run, or a survivor in a source with more importing tests than the run used never blocks.

Accept markers

A finding can be correct and still on purpose. Accept it with a comment that says why, next to the code, so the reviewer sees both:

// dry-duplicate-ok: v1 and v2 parsers must change apart
export function parseV2(input: string) {

// mutation-equivalent: m[2] is never "", so ?? and || agree
const cents = Number((m[2] ?? "").padEnd(2, "0"));

• dry-duplicate-ok: <reason> goes inside the changed function or in the comment lines right above it. A marker on the other, unchanged function does not count: it would excuse every future copy.
• mutation-equivalent: <reason> goes on the mutant's line or in the comment lines right above it. It covers every surviving mutant on that line. A killed mutant stays killed.
• A marker without a reason accepts nothing, and only a real comment counts: marker text inside a string accepts nothing. The report lists each accepted finding with its reason.
• Use a marker only after the repair below did not apply. A marker that only hides a missing test is gaming the gate.

DRY gate

make dry-check (or bun scripts/dry/check.ts --base <ref>) compares each changed function with every production function in src/. The scorer is dryer: it drops names, literals and locals, then scores the Jaccard similarity of the structure. Exit 0 no findings, 1 findings, 2 tool error. CI shows the same report in the Quality / DRY job summary.

warning  new-duplicate score 1.00 src/x.ts:41-46 feeBucket
         matches src/x.ts:34-39 centsBucket

• A finding needs a score of 0.82 or more (the dryer default), at least 4 lines and 20 syntax nodes.
• Only pairs that the change made are findings: a new function that copies another one, or an edit that makes two functions match. An edit to one side of a pair that already matched on main is quiet. The gate does not track moves across files: a function moved into another file reports its old pairs again. Say so in the PR; it is not a new duplicate.
• Files under test, story and fixture paths do not count (the CRAP gate's production-file rule).

Repair

1. If both functions must change together (one rule, one format, one protocol), extract the shared shape into one function and call it from both places.
2. If they only look alike and must change apart (two different domains that happen to share a shape today), keep both and add a dry-duplicate-ok: marker that says why.

Never merge two functions only to clear a DRY finding. A wrong abstraction costs more than a copy.

Mutation gate

make mutate-check (or bun scripts/mutate/check.ts --base <ref>) makes small changes ("mutants") in the functions you changed, one at a time: === to !==, > to >=, && to ||, ?? to ||, true to false, 0 to 1, and more (mutator's rules). For each mutant it runs the Bun unit tests that import the file. A mutant that no test fails on "survived": no test checks that behaviour. It runs on Linux and macOS only (it kills each test's process group); on Windows it is a tool error.

mutate-check: 2 survived, 7 killed, 0 uncovered, 0 without a test, 0 not run
  src/x.ts  (tests: src/x.test.ts, src/y.test.ts)
    survived :61 === -> !==  parseCap

• Tests: the colocated test first, then the nearest other unit tests that import the file directly, at most 10. Each test file runs in its own bun test process, in a private copy of the tracked files. The first failing file kills the mutant. A timeout (10x the file's own time, at least 2 s) also kills it.
• equivalent: a survivor under a mutation-equivalent: marker.
• Exit 0 no survivors, 1 survivors, 2 tool error, 3 baseline failure: a test file failed without a mutant, so the run dropped it. Fix that test first.
• uncovered: with --coverage <lcov> (CI uses the Test / Unit reports), a site on a line that no test ran does not run. no-test: no passing unit test imports the file. not-run: the run stopped at its limit (CI: 300 mutants or 15 minutes). error: the runner crashed on that one mutant; the report gives the reason, and the other mutants still count.
• Locally it runs on 4 workers at most (--workers N). Start with a small change: every site in a touched function runs.

Repair

1. Write a test that fails for the mutant. Assert the behaviour that the mutant breaks (the boundary, the other branch), not the line.
2. If no input can tell the mutant from the original, it is equivalent. For example, m[2] ?? "" and m[2] || "" are the same when m[2] is never "". Add a mutation-equivalent: marker that says why.

Never change production code only to kill a mutant, and never add a test without a real assertion. The CRAP gate's anti-gaming rules apply here too.