test(signals): cover buildReviewRiskExplanation's 5-way branch logic (#9287) (#9338)

Existing coverage only checked REST/MCP parity for the shared review-risk
builder, never asserting what each of the five recommendation branches
(likely_duplicate, maintainer_lane, needs_author, review, watch) actually
resolves to. Add direct unit tests with minimal fixtures for each branch.

Author: nghetien

test/unit/review-risk.test.ts

@@ -0,0 +1,102 @@
+import { describe, expect, it } from "vitest";
+import { buildReviewRiskExplanation } from "../../src/signals/review-risk";
+import type { IssueRecord, PullRequestRecord, RegistryRepoConfig, RepositoryRecord } from "../../src/types";
+
+function repo(fullName: string, overrides: Partial<RegistryRepoConfig> = {}): RepositoryRecord {
+  const [owner, name] = fullName.split("/") as [string, string];
+  return {
+    fullName,
+    owner,
+    name,
+    isInstalled: true,
+    isRegistered: true,
+    isPrivate: false,
+    registryConfig: {
+      repo: fullName,
+      emissionShare: 0.02,
+      issueDiscoveryShare: 0,
+      labelMultipliers: {},
+      maintainerCut: 0,
+      raw: {},
+      ...overrides,
+    },
+  };
+}
+
+function issue(repoFullName: string, number: number, title: string, overrides: Partial<IssueRecord> = {}): IssueRecord {
+  return { repoFullName, number, title, state: "open", labels: [], linkedPrs: [], ...overrides };
+}
+
+function pr(repoFullName: string, number: number, title: string, overrides: Partial<PullRequestRecord> = {}): PullRequestRecord {
+  return { repoFullName, number, title, state: "open", labels: [], linkedIssues: [], ...overrides };
+}
+
+// #9287: buildReviewRiskExplanation previously only had parity coverage (does the REST route match the
+// MCP tool?) with no test asserting what each of its five recommendation branches actually resolves to.
+describe("buildReviewRiskExplanation", () => {
+  it("recommends likely_duplicate when a high-risk collision cluster is present", () => {
+    const activeRepo = repo("acme/widgets");
+    const dupIssue = issue(activeRepo.fullName, 100, "Duplicate work");
+    const firstCandidate = pr(activeRepo.fullName, 101, "First candidate fix", { linkedIssues: [100] });
+    const secondCandidate = pr(activeRepo.fullName, 102, "Second candidate fix", { linkedIssues: [100] });
+    const result = buildReviewRiskExplanation({
+      input: { repoFullName: activeRepo.fullName, title: "Third candidate fix", linkedIssues: [100] },
+      repo: activeRepo,
+      issues: [dupIssue],
+      pullRequests: [firstCandidate, secondCandidate],
+    });
+    expect(result.recommendation).toBe("likely_duplicate");
+    expect(result.summary).toBe(`LoopOver review-risk explanation for ${activeRepo.fullName}.`);
+  });
+
+  it("recommends maintainer_lane when the contributor login owns the repo", () => {
+    const result = buildReviewRiskExplanation({
+      input: { repoFullName: "acme/widgets", title: "Repo housekeeping", contributorLogin: "acme" },
+      repo: null,
+      issues: [],
+      pullRequests: [],
+    });
+    expect(result.recommendation).toBe("maintainer_lane");
+    expect(result.roleContext?.maintainerLane).toBe(true);
+    expect(result.summary).toBe("LoopOver review-risk explanation for acme/widgets.");
+  });
+
+  it("recommends needs_author when preflight status is needs_work", () => {
+    const activeRepo = repo("acme/widgets");
+    const result = buildReviewRiskExplanation({
+      input: { repoFullName: activeRepo.fullName, title: "Fix pagination", body: "Just a fix, no context." },
+      repo: activeRepo,
+      issues: [],
+      pullRequests: [],
+    });
+    expect(result.preflight.status).toBe("needs_work");
+    expect(result.recommendation).toBe("needs_author");
+    expect(result.summary).toBe(`LoopOver review-risk explanation for ${activeRepo.fullName}.`);
+  });
+
+  it("recommends review when preflight status is ready", () => {
+    const activeRepo = repo("acme/widgets");
+    const result = buildReviewRiskExplanation({
+      input: { repoFullName: activeRepo.fullName, title: "Fix pagination", body: "Fixes #1", linkedIssues: [1] },
+      repo: activeRepo,
+      issues: [],
+      pullRequests: [],
+    });
+    expect(result.preflight.status).toBe("ready");
+    expect(result.recommendation).toBe("review");
+    expect(result.summary).toBe(`LoopOver review-risk explanation for ${activeRepo.fullName}.`);
+  });
+
+  it("recommends watch when the repo lane is unavailable and the author is not a maintainer", () => {
+    const result = buildReviewRiskExplanation({
+      input: { repoFullName: "missing/repo", title: "Docs note" },
+      repo: null,
+      issues: [],
+      pullRequests: [],
+    });
+    expect(result.preflight.status).toBe("hold");
+    expect(result.recommendation).toBe("watch");
+    expect(result.roleContext).toBeNull();
+    expect(result.summary).toBe("LoopOver review-risk explanation for missing/repo.");
+  });
+});