chore: import upstream snapshot with attribution

tests/unit/check-complexity.test.ts

@@ -0,0 +1,46 @@
+import { test } from "node:test";
+import assert from "node:assert";
+import { evaluateComplexity } from "../../scripts/check/check-complexity.mjs";
+
+// The .mjs module has no .d.ts; type the pure comparator locally so the test file
+// stays free of explicit `any` (ratchet 3482 — zero new warnings allowed).
+type ComplexityVerdict = { regressed: boolean; improved: boolean };
+const evaluate = evaluateComplexity as (current: number, baseline: number) => ComplexityVerdict;
+
+const BASELINE = 1739;
+
+test("equal to baseline passes", () => {
+  const r = evaluate(BASELINE, BASELINE);
+  assert.equal(r.regressed, false);
+  assert.equal(r.improved, false);
+});
+
+test("one more violation is a regression", () => {
+  const r = evaluate(BASELINE + 1, BASELINE);
+  assert.equal(r.regressed, true);
+  assert.equal(r.improved, false);
+});
+
+test("a large increase is a regression", () => {
+  const r = evaluate(BASELINE + 200, BASELINE);
+  assert.equal(r.regressed, true);
+});
+
+test("one fewer violation is an improvement (ratchet down)", () => {
+  const r = evaluate(BASELINE - 1, BASELINE);
+  assert.equal(r.regressed, false);
+  assert.equal(r.improved, true);
+});
+
+test("zero violations is an improvement and never regresses", () => {
+  const r = evaluate(0, BASELINE);
+  assert.equal(r.regressed, false);
+  assert.equal(r.improved, true);
+});
+
+test("exact-integer comparison — no epsilon tolerance", () => {
+  // Unlike the duplication gate (float %), complexity is an integer count: any increase
+  // at all must fail, with no slack.
+  assert.equal(evaluate(11, 10).regressed, true);
+  assert.equal(evaluate(10, 10).regressed, false);
+});