feat(scoring): surface branch eligibility in the score breakdown

src/services/score-breakdown.ts

@@ -197,6 +197,62 @@ function issueMultiplierBreakdown(preview: ScorePreviewResult): ScoreMultiplierB
   return { component: "issueMultiplier", band, summary, lever, leverageScore };
 }
 
+// Sibling of issueMultiplierBreakdown: branch/base eligibility gates the standard linked-issue multiplier
+// even when issue metadata looks plausible (#90 / #178). Surfaced here so miners see the same actionable
+// breakdown other eligibility gates already provide.
+function branchEligibilityBreakdown(preview: ScorePreviewResult): ScoreMultiplierBreakdown {
+  const branch = preview.branchEligibility;
+  if (!branch.required || branch.status === "not_required") {
+    return {
+      component: "branchEligibility",
+      band: "neutral",
+      summary: "Branch eligibility is not required for this preview (no standard linked-issue lane).",
+      lever: "Use standard linked-issue mode when branch/base proof is required for issue-solving PRs.",
+      leverageScore: 0,
+    };
+  }
+  if (
+    branch.status === "eligible" &&
+    branch.evidence === "provided" &&
+    !branch.stale &&
+    branch.source !== "user_supplied"
+  ) {
+    return {
+      component: "branchEligibility",
+      band: "full",
+      summary: "Branch/base eligibility is confirmed for standard linked-issue scoring.",
+      lever: "Keep branch and base metadata aligned with the repo's registered eligibility rules.",
+      leverageScore: 5,
+    };
+  }
+  if (branch.status === "ineligible") {
+    return {
+      component: "branchEligibility",
+      band: "blocked",
+      summary: branch.reason
+        ? `Branch/base eligibility is confirmed ineligible (${branch.reason}).`
+        : "Branch/base eligibility is confirmed ineligible; standard linked-issue scoring is blocked.",
+      lever: "Use an eligible branch or remove linked-issue assumptions before relying on this preview.",
+      leverageScore: 90,
+    };
+  }
+  const summary =
+    branch.evidence === "missing"
+      ? "Branch eligibility evidence is missing; standard linked-issue multiplier assumptions are not confirmed."
+      : branch.stale
+        ? "Branch eligibility evidence is stale; standard linked-issue multiplier assumptions need refresh."
+        : branch.status === "unknown" && branch.source === "user_supplied"
+          ? "Branch eligibility evidence is user-supplied; verified metadata is required for standard linked-issue scoring."
+          : branch.status === "unknown"
+            ? "Branch eligibility is unknown; standard linked-issue multiplier assumptions are not confirmed."
+            : branch.source === "user_supplied"
+              ? "Branch eligibility evidence is user-supplied; verified metadata is required for standard linked-issue scoring."
+              : "Branch eligibility is not confirmed; standard linked-issue multiplier assumptions are not applied.";
+  const lever = "Refresh branch/base eligibility metadata before relying on linked-issue assumptions.";
+  const leverageScore = branch.evidence === "missing" || branch.status === "unknown" ? 75 : 65;
+  return { component: "branchEligibility", band: "reduced", summary, lever, leverageScore };
+}
+
 function reviewPenaltyBreakdown(preview: ScorePreviewResult): ScoreMultiplierBreakdown {
   const { reviewPenaltyMultiplier } = preview.scoreEstimate;
   const band = bandForMultiplier(reviewPenaltyMultiplier, false);
@@ -312,6 +368,7 @@ export function explainScoreBreakdown(preview: ScorePreviewResult): ScoreBreakdo
     contributionBonusBreakdown(preview),
     labelMultiplierBreakdown(preview),
     issueMultiplierBreakdown(preview),
+    branchEligibilityBreakdown(preview),
     credibilityBreakdown(preview),
     reviewPenaltyBreakdown(preview),
     reviewCollateralBreakdown(preview),

test/unit/score-breakdown.test.ts

@@ -79,6 +79,7 @@ describe("explainScoreBreakdown", () => {
         "contributionBonus",
         "labelMultiplier",
         "issueMultiplier",
+        "branchEligibility",
         "credibilityMultiplier",
         "reviewPenaltyMultiplier",
         "reviewCollateralMultiplier",
@@ -94,7 +95,7 @@ describe("explainScoreBreakdown", () => {
       expect(["full", "reduced", "neutral", "blocked"]).toContain(component.band);
     }
     expect(breakdown.highestLeverageLever.component).toBeTruthy();
-    expect(breakdown.highestLeverageLever.lever).toMatch(/merge|close|credibility|open PR|linked issue|density|review/i);
+    expect(breakdown.highestLeverageLever.lever).toMatch(/merge|close|credibility|open PR|linked issue|density|review|branch/i);
     expect(JSON.stringify(breakdown)).not.toMatch(FORBIDDEN);
     // No open issues → within the allowance → full band on the open-issue gate.
     expect(breakdown.components.find((entry) => entry.component === "openIssueMultiplier")).toMatchObject({ band: "full" });
@@ -122,6 +123,186 @@ describe("explainScoreBreakdown", () => {
     expect(JSON.stringify(blocked)).not.toMatch(FORBIDDEN);
   });
 
+  it("explains branch eligibility as neutral (not required), full (eligible), blocked (ineligible), and reduced (unknown/missing/stale)", () => {
+    const notRequired = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: { repoFullName: repo.fullName, sourceTokenScore: 40, totalTokenScore: 60, sourceLines: 80, linkedIssueMode: "none" },
+      }),
+    );
+    expect(notRequired.components.find((entry) => entry.component === "branchEligibility")).toMatchObject({ band: "neutral" });
+
+    const eligible = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "validated", source: "official_mirror", issueNumbers: [3], solvedByPullRequests: [44] },
+          branchEligibility: { status: "eligible", source: "github_metadata", checkedAt: "2026-05-30T00:00:00.000Z" },
+        },
+      }),
+    );
+    expect(eligible.components.find((entry) => entry.component === "branchEligibility")).toMatchObject({ band: "full" });
+
+    const userSuppliedEligible = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "validated", source: "official_mirror", issueNumbers: [3], solvedByPullRequests: [44] },
+          branchEligibility: { status: "eligible", source: "user_supplied" },
+        },
+      }),
+    );
+    expect(userSuppliedEligible.components.find((entry) => entry.component === "branchEligibility")).toMatchObject({
+      band: "reduced",
+      summary: expect.stringMatching(/user-supplied/i),
+    });
+
+    const ineligible = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "validated", source: "official_mirror", issueNumbers: [3], solvedByPullRequests: [44] },
+          branchEligibility: { status: "ineligible", source: "github_metadata", reason: "head branch is not eligible" },
+        },
+      }),
+    );
+    const ineligibleBranch = ineligible.components.find((entry) => entry.component === "branchEligibility");
+    expect(ineligibleBranch).toMatchObject({ band: "blocked", leverageScore: 90 });
+    expect(ineligibleBranch?.summary).toMatch(/head branch is not eligible/i);
+    expect(ineligibleBranch?.lever).toMatch(/eligible branch/i);
+
+    const ineligibleNoReason = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "raw", source: "github_cache", issueNumbers: [12] },
+          branchEligibility: { status: "ineligible", source: "github_metadata" },
+        },
+      }),
+    );
+    expect(ineligibleNoReason.components.find((entry) => entry.component === "branchEligibility")?.summary).toMatch(
+      /confirmed ineligible; standard linked-issue scoring is blocked/i,
+    );
+
+    const unknownMetadata = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "plausible", source: "github_cache", issueNumbers: [4] },
+          branchEligibility: { status: "unknown", source: "github_metadata" },
+        },
+      }),
+    );
+    expect(unknownMetadata.components.find((entry) => entry.component === "branchEligibility")?.summary).toMatch(/unknown/i);
+
+    const missing = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "raw", source: "github_cache", issueNumbers: [12] },
+        },
+      }),
+    );
+    expect(missing.components.find((entry) => entry.component === "branchEligibility")).toMatchObject({
+      band: "reduced",
+      summary: expect.stringMatching(/evidence is missing/i),
+    });
+
+    const stale = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "plausible", source: "github_cache", issueNumbers: [4] },
+          branchEligibility: { status: "eligible", source: "local_metadata", stale: true, checkedAt: "2026-05-01T00:00:00.000Z" },
+        },
+      }),
+    );
+    expect(stale.components.find((entry) => entry.component === "branchEligibility")?.summary).toMatch(/stale/i);
+
+    const userSupplied = explainScoreBreakdown(
+      buildScorePreview({
+        repo,
+        snapshot,
+        input: {
+          repoFullName: repo.fullName,
+          sourceTokenScore: 40,
+          totalTokenScore: 60,
+          sourceLines: 80,
+          linkedIssueMode: "standard",
+          linkedIssueContext: { status: "plausible", source: "github_cache", issueNumbers: [4] },
+          branchEligibility: { status: "unknown" },
+        },
+      }),
+    );
+    expect(userSupplied.components.find((entry) => entry.component === "branchEligibility")?.summary).toMatch(/user-supplied/i);
+    expect(JSON.stringify(ineligible)).not.toMatch(FORBIDDEN);
+  });
+
+  it("prioritizes ineligible branch metadata above invalid linked-issue context", () => {
+    const preview = buildScorePreview({
+      repo,
+      snapshot,
+      input: {
+        repoFullName: repo.fullName,
+        sourceTokenScore: 80,
+        totalTokenScore: 120,
+        sourceLines: 60,
+        openPrCount: 0,
+        credibility: 1,
+        linkedIssueMode: "standard",
+        linkedIssueContext: { status: "invalid", source: "github_cache", issueNumbers: [9], reason: "Issue #9 is closed." },
+        branchEligibility: { status: "ineligible", source: "github_metadata", reason: "head branch is not eligible" },
+      },
+    });
+
+    const breakdown = explainScoreBreakdown(preview);
+    expect(breakdown.components.find((entry) => entry.component === "branchEligibility")).toMatchObject({ band: "blocked" });
+    expect(breakdown.highestLeverageLever.component).toBe("branchEligibility");
+  });
+
   it("explains an over-threshold open-issue count as a blocked open-issue spam gate", () => {
     const preview = buildScorePreview({
       repo,
@@ -374,6 +555,7 @@ describe("explainScoreBreakdown", () => {
         credibility: 1,
         linkedIssueMode: "standard",
         linkedIssueContext: { status: "invalid", source: "github_cache", issueNumbers: [9], reason: "Issue #9 is closed." },
+        branchEligibility: { status: "eligible", source: "github_metadata" },
       },
     });