feat(signals): validate label-multiplier ranges in config quality

src/signals/engine.ts

@@ -1048,6 +1048,25 @@ export function buildConfigQuality(
       action: "Verify those labels exist and are actually used by maintainers or trusted automation.",
     });
   }
+  // A label multiplier must be a positive, finite number — a penalty multiplier is below 1 but still
+  // positive, so it is valid; 0, negative, NaN, or Infinity are config errors that would silently
+  // misweight scoring. Distinct from notObservedConfiguredLabels (which checks whether a label is *used*,
+  // not whether its multiplier is *valid*).
+  // Surface each bad multiplier as `label=value` so a maintainer sees the offending value inline.
+  const invalidLabelMultipliers = Object.entries(repo?.registryConfig?.labelMultipliers ?? {})
+    .filter(([, multiplier]) => !(typeof multiplier === "number" && Number.isFinite(multiplier) && multiplier > 0))
+    .map(([label, multiplier]) => `${label}=${String(multiplier)}`)
+    .sort();
+  if (invalidLabelMultipliers.length > 0) {
+    score -= Math.min(30, invalidLabelMultipliers.length * 10);
+    findings.push({
+      code: "invalid_label_multipliers",
+      severity: "warning",
+      title: "Configured label multipliers are out of range",
+      detail: `Label multipliers must be positive, finite numbers; these are not: ${invalidLabelMultipliers.join(", ")}.`,
+      action: "Set each flagged label multiplier to a positive, finite number (a penalty multiplier below 1 is allowed) in the registry config.",
+    });
+  }
 
   const finalScore = clamp(score, 0, 100);
   return {

test/unit/signals.test.ts

@@ -597,6 +597,39 @@ describe("world-class backend signals", () => {
     expect(noMultiplierQuality.findings.map((finding) => finding.code)).toContain("trusted_labels_without_multipliers");
   });
 
+  it("flags non-positive, non-finite, or non-numeric label multipliers as a config error", () => {
+    const badRepo = {
+      ...repo,
+      registryConfig: {
+        ...repo.registryConfig!,
+        labelMultipliers: { bug: -1, stale: 0, broken: Number.NaN, weird: "x" as unknown as number, good: 1.2, penalty: 0.5 },
+      },
+    };
+    // Observe every configured label so the unrelated "not observed" penalty does not also fire.
+    const observed = [{ ...issues[0]!, labels: ["bug", "stale", "broken", "weird", "good", "penalty"] }];
+    const quality = buildConfigQuality(badRepo, observed, [], repo.fullName);
+    const invalid = quality.findings.find((finding) => finding.code === "invalid_label_multipliers");
+    expect(invalid).toBeDefined();
+    // Each bad multiplier is named with its value (sorted); valid ones are not listed.
+    expect(invalid?.detail).toMatch(/broken=NaN, bug=-1, stale=0, weird=x/);
+    expect(invalid?.detail).not.toMatch(/good|penalty/);
+    // Four invalid entries deduct the capped 30 points; valid ones do not contribute.
+    const baseline = buildConfigQuality({ ...badRepo, registryConfig: { ...badRepo.registryConfig!, labelMultipliers: { good: 1.2, penalty: 0.5 } } }, observed, [], repo.fullName).score;
+    expect(quality.score).toBe(baseline - 30);
+  });
+
+  it("does not flag valid positive label multipliers, including penalty (<1) multipliers", () => {
+    const okRepo = { ...repo, registryConfig: { ...repo.registryConfig!, labelMultipliers: { feature: 1.25, refactor: 0.5 } } };
+    const quality = buildConfigQuality(okRepo, [{ ...issues[0]!, labels: ["feature", "refactor"] }], [], repo.fullName);
+    expect(quality.findings.map((finding) => finding.code)).not.toContain("invalid_label_multipliers");
+  });
+
+  it("treats a repo with no labelMultipliers key as having no invalid multipliers", () => {
+    const noLabelsRepo = { ...repo, registryConfig: { ...repo.registryConfig!, labelMultipliers: undefined as unknown as Record<string, number> } };
+    const quality = buildConfigQuality(noLabelsRepo, [], [], repo.fullName);
+    expect(quality.findings.map((finding) => finding.code)).not.toContain("invalid_label_multipliers");
+  });
+
   it("keeps contributor detection and comment modes conservative", () => {
     const currentPr = pullRequests[0]!;
     const settings: RepositorySettings = {