test(router-eval): assert regression reasons instead of counting entries

The test named 'captures AIQ and cost regressions' only asserted
regressions.length > 0, which re-implements a condition the production
comparison owns and passes even if either regression stops being
reported. Assert the actual AIQ and cost reasons instead — strictly
stronger and clears the weakened-assert gate.

changelog.d/maintenance/router-eval-test-assert-strengthen.md

@@ -0,0 +1 @@
+- Strengthen the `compareRouterEvalRuns` regression test to assert the actual AIQ and cost regression reasons instead of counting entries, clearing the weakened-assert (test-masking) gate on the release tip.

tests/unit/router-eval.test.ts

@@ -73,7 +73,14 @@ test("compareRouterEvalRuns captures AIQ and cost regressions", () => {
     relativeCostIncrease: 1.2,
   });
 
-  assert.equal(comparison.regressions.length > 0, true);
+  assert.ok(
+    comparison.regressions.some((reason) => reason.startsWith("AIQ dropped by")),
+    "expected an AIQ regression to be reported"
+  );
+  assert.ok(
+    comparison.regressions.some((reason) => reason.startsWith("cost increased by")),
+    "expected a cost regression to be reported"
+  );
   assert.equal(comparison.delta.aiq <= 0, true);
   assert.equal(comparison.delta.costUsd > 0, true);
 });