feat(scoring): surface tied-leverage disclosure in score breakdown

src/services/score-breakdown.ts

@@ -20,6 +20,11 @@ export type ScoreBreakdownExplanation = {
   highestLeverageLever: {
     component: string;
     lever: string;
+    /** Other components that tie with the selected top component at the same leverageScore
+     *  (excludes the selected top component itself). Ordered alphabetically (same tie-breaker
+     *  used to pick the top component). Surfaced so a contributor can see the alphabetical
+     *  tie-breaker isn't a strictly-dominant choice. Empty when no tie exists. */
+    tiedLeverageComponents: string[];
     reason: string;
   };
 };
@@ -361,15 +366,23 @@ function gateHighlightsFor(preview: ScorePreviewResult): ScoreBreakdownExplanati
 function pickHighestLeverage(components: ScoreMultiplierBreakdown[]): ScoreBreakdownExplanation["highestLeverageLever"] {
   const ranked = [...components].sort((left, right) => right.leverageScore - left.leverageScore || left.component.localeCompare(right.component));
   const top = ranked[0]!;
+  // Surface any components tied at the top leverageScore so the alphabetical tie-breaker
+  // (localeCompare above) is not silently dominant — a contributor fixing only the named top
+  // component would miss equally-impactful tied components. Empty when no tie exists.
+  const tied = ranked.filter((entry, idx) => idx > 0 && entry.leverageScore === top.leverageScore).map((entry) => entry.component);
+  const tiedClause = tied.length > 0
+    ? ` (${top.component} ties with ${tied.join(", ")} at the same leverage score; any of these is the highest-leverage lever.)`
+    : "";
   const reason =
     top.band === "blocked"
-      ? `${top.component} is fully blocking or zeroing part of the preview right now.`
+      ? `${top.component} is fully blocking or zeroing part of the preview right now.${tiedClause}`
       : top.band === "reduced"
-        ? `${top.component} is the largest remaining reducer in the multiplier stack.`
-        : `${top.component} is the best next optimization lever among non-blocking multipliers.`;
+        ? `${top.component} is the largest remaining reducer in the multiplier stack.${tiedClause}`
+        : `${top.component} is the best next optimization lever among non-blocking multipliers.${tiedClause}`;
   return {
     component: top.component,
     lever: top.lever,
+    tiedLeverageComponents: tied,
     reason: sanitizePublicComment(reason),
   };
 }

test/unit/score-breakdown.test.ts

@@ -677,4 +677,55 @@ describe("explainScoreBreakdown", () => {
     expect(isSaturated.summary).toMatch(/saturated near the score cap/);
     expect(JSON.stringify(explainScoreBreakdown(saturated))).not.toMatch(FORBIDDEN);
   });
+
+  it("surfaces tied-leverage components when multiple levers share the top leverageScore", () => {
+    // Both openPrMultiplier and openIssueMultiplier blocked at leverageScore 100.
+    // With existingContributorTokenScore = 0, openPrThreshold = 2 and openIssueThreshold = 2.
+    // openPrCount = 3 > 2 → blocked (leverageScore 100).
+    // openIssueCount = 3 > 2 → blocked (leverageScore 100).
+    // Alphabetical winner: "openIssueMultiplier" (I < P), tied component: "openPrMultiplier".
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        sourceTokenScore: 100,
+        totalTokenScore: 200,
+        sourceLines: 100,
+        openPrCount: 3,
+        openIssueCount: 3,
+        existingContributorTokenScore: 0,
+        credibility: 1,
+      },
+    });
+    const breakdown = explainScoreBreakdown(preview);
+    const top = breakdown.highestLeverageLever;
+    expect(top.component).toBe("openIssueMultiplier");
+    expect(top.tiedLeverageComponents).toEqual(["openPrMultiplier"]);
+    expect(top.reason).toMatch(/openIssueMultiplier ties with openPrMultiplier at the same leverage score/);
+    expect(breakdown.components.find((c) => c.component === "openIssueMultiplier")?.leverageScore).toBe(100);
+    expect(breakdown.components.find((c) => c.component === "openPrMultiplier")?.leverageScore).toBe(100);
+  });
+
+  it("returns empty tiedLeverageComponents when no tie exists at the top leverageScore", () => {
+    // Single top lever (credibilityMultiplier at 85) — no tie.
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        sourceTokenScore: 100,
+        totalTokenScore: 200,
+        sourceLines: 100,
+        openPrCount: 0,
+        openIssueCount: 0,
+        existingContributorTokenScore: 0,
+        credibility: 0.01,
+      },
+    });
+    const breakdown = explainScoreBreakdown(preview);
+    const top = breakdown.highestLeverageLever;
+    expect(top.tiedLeverageComponents).toEqual([]);
+    expect(top.reason).not.toMatch(/ties with/);
+  });
 });