feat(scoring): explain issue-discovery validity floor in score breakdown

src/services/score-breakdown.ts

@@ -131,6 +131,36 @@ function mergedHistoryBreakdown(preview: ScorePreviewResult): ScoreMultiplierBre
   };
 }
 
+// Sibling of mergedHistoryBreakdown for the issue-discovery validity floor (upstream
+// MIN_VALID_SOLVED_ISSUES and MIN_ISSUE_CREDIBILITY): when linked-issue scoring is active and
+// contributor history is observed, falling below either floor zeroes the preview.
+function issueDiscoveryHistoryBreakdown(preview: ScorePreviewResult): ScoreMultiplierBreakdown {
+  const { issueDiscoveryHistoryMultiplier } = preview.scoreEstimate;
+  const { validSolvedIssues, validSolvedIssuesFloor, issueCredibility, issueCredibilityFloor } = preview.gates;
+  if (validSolvedIssues === undefined || issueCredibility === undefined) {
+    return {
+      component: "issueDiscoveryHistoryMultiplier",
+      band: "neutral",
+      summary: `Issue-discovery validity floor is not enforced for this preview (contributor issue-history is unobserved; upstream floors are ${validSolvedIssuesFloor} valid solved and ${issueCredibilityFloor} credibility).`,
+      lever: "No action needed for this preview; the validity floor applies once issue-discovery history is observed.",
+      leverageScore: 0,
+    };
+  }
+  const band = bandForMultiplier(issueDiscoveryHistoryMultiplier);
+  const meetsFloor = validSolvedIssues >= validSolvedIssuesFloor && issueCredibility >= issueCredibilityFloor;
+  return {
+    component: "issueDiscoveryHistoryMultiplier",
+    band,
+    summary: meetsFloor
+      ? `Issue-discovery history (${validSolvedIssues} valid solved, credibility ${roundBand(issueCredibility)}) meets upstream floors (${validSolvedIssuesFloor} valid solved, ${issueCredibilityFloor} credibility).`
+      : `Issue-discovery history (${validSolvedIssues} valid solved, credibility ${roundBand(issueCredibility)}) is below upstream floors (${validSolvedIssuesFloor} valid solved, ${issueCredibilityFloor} credibility), so this preview is zeroed.`,
+    lever: meetsFloor
+      ? "Keep building valid solved-issue history with strong issue credibility."
+      : "Close more valid solved issues and improve issue credibility before relying on issue-discovery scoring.",
+    leverageScore: meetsFloor ? 8 : 100,
+  };
+}
+
 // Upstream time-decay (#703), env-gated by SCORING_TIME_DECAY_ENABLED (default OFF) and opted into per-preview
 // via input.applyTimeDecay. When the flag is off (the common case) or the PR is fresh, the multiplier is 1 and
 // the breakdown reads as "not enabled" / "fresh" — surfacing the value is a no-op for those previews but
@@ -318,6 +348,7 @@ export function explainScoreBreakdown(preview: ScorePreviewResult): ScoreBreakdo
     openPrBreakdown(preview),
     openIssueBreakdown(preview),
     mergedHistoryBreakdown(preview),
+    issueDiscoveryHistoryBreakdown(preview),
     timeDecayBreakdown(preview),
   ].map((entry) => ({
     ...entry,

test/unit/score-breakdown.test.ts

@@ -85,6 +85,7 @@ describe("explainScoreBreakdown", () => {
         "openPrMultiplier",
         "openIssueMultiplier",
         "mergedHistoryMultiplier",
+        "issueDiscoveryHistoryMultiplier",
         "timeDecayMultiplier",
       ]),
     );
@@ -122,6 +123,57 @@ describe("explainScoreBreakdown", () => {
     expect(JSON.stringify(blocked)).not.toMatch(FORBIDDEN);
   });
 
+  it("explains the issue-discovery validity floor as neutral (unobserved), full (meets floor), and blocked (below floor)", () => {
+    const issueDiscoveryRepo: RepositoryRecord = {
+      ...repo,
+      registryConfig: { ...repo.registryConfig!, issueDiscoveryShare: 0.25 },
+    };
+    const baseInput = {
+      repoFullName: issueDiscoveryRepo.fullName,
+      contributorLogin: "miner",
+      sourceTokenScore: 40,
+      totalTokenScore: 60,
+      sourceLines: 80,
+      openPrCount: 0,
+      credibility: 1,
+      mergedPullRequests: 5,
+      linkedIssueMode: "standard" as const,
+    };
+
+    const unobserved = explainScoreBreakdown(buildScorePreview({ repo: issueDiscoveryRepo, snapshot, input: baseInput }));
+    expect(unobserved.components.find((entry) => entry.component === "issueDiscoveryHistoryMultiplier")).toMatchObject({
+      band: "neutral",
+      leverageScore: 0,
+    });
+
+    const meets = explainScoreBreakdown(
+      buildScorePreview({
+        repo: issueDiscoveryRepo,
+        snapshot,
+        input: { ...baseInput, validSolvedIssues: 4, issueCredibility: 0.9 },
+      }),
+    );
+    expect(meets.components.find((entry) => entry.component === "issueDiscoveryHistoryMultiplier")).toMatchObject({
+      band: "full",
+      summary: expect.stringMatching(/4 valid solved, private context 0.9/i),
+    });
+
+    const blocked = explainScoreBreakdown(
+      buildScorePreview({
+        repo: issueDiscoveryRepo,
+        snapshot,
+        input: { ...baseInput, validSolvedIssues: 1, issueCredibility: 0.5 },
+      }),
+    );
+    expect(blocked.components.find((entry) => entry.component === "issueDiscoveryHistoryMultiplier")).toMatchObject({
+      band: "blocked",
+      summary: expect.stringMatching(/private context.*zeroed/i),
+      leverageScore: 100,
+    });
+    expect(blocked.highestLeverageLever.lever).toMatch(/valid solved issues|issue credibility/i);
+    expect(JSON.stringify(blocked)).not.toMatch(FORBIDDEN);
+  });
+
   it("explains an over-threshold open-issue count as a blocked open-issue spam gate", () => {
     const preview = buildScorePreview({
       repo,