feat(FN-4168): complete Step 2 — add stalled review detector

Fusion-Task-Id: FN-4168
Fusion-Task-Lineage: 781ffc66-cb1c-42b9-85e1-e5cbe0655863

packages/core/src/__tests__/stalled-review-detector.test.ts

@@ -0,0 +1,114 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  STALLED_REVIEW_INVALID_TRANSITION_PATTERN,
+  STALLED_REVIEW_INVALID_TRANSITION_THRESHOLD,
+  STALLED_REVIEW_REENQUEUE_PATTERN,
+  STALLED_REVIEW_REENQUEUE_THRESHOLD,
+  STALLED_REVIEW_WINDOW_MS,
+  detectStalledReview,
+} from "../stalled-review-detector.js";
+import type { TaskLogEntry } from "../types.js";
+
+function entry(timestamp: string, action: string, outcome?: string): TaskLogEntry {
+  return { timestamp, action, outcome };
+}
+
+describe("detectStalledReview", () => {
+  const now = Date.parse("2026-05-12T12:00:00.000Z");
+
+  it("fires reenqueue-churn at threshold", () => {
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [
+        entry("2026-05-12T11:30:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+        entry("2026-05-12T11:40:00.000Z", `noise ${STALLED_REVIEW_REENQUEUE_PATTERN}`),
+        entry("2026-05-12T11:50:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+      ],
+    }, { now });
+
+    expect(signal?.heuristic).toBe("reenqueue-churn");
+    expect(signal?.matchCount).toBe(STALLED_REVIEW_REENQUEUE_THRESHOLD);
+  });
+
+  it("does not fire reenqueue-churn below threshold", () => {
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [
+        entry("2026-05-12T11:30:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+        entry("2026-05-12T11:40:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+      ],
+    }, { now });
+
+    expect(signal).toBeUndefined();
+  });
+
+  it("fires invalid-transition-loop at threshold", () => {
+    const invalid = "Invalid transition: 'todo' → 'done'";
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [
+        entry("2026-05-12T11:30:00.000Z", "merge recovery", invalid),
+        entry("2026-05-12T11:40:00.000Z", invalid),
+      ],
+    }, { now });
+
+    expect(invalid).toMatch(STALLED_REVIEW_INVALID_TRANSITION_PATTERN);
+    expect(signal?.heuristic).toBe("invalid-transition-loop");
+    expect(signal?.matchCount).toBe(STALLED_REVIEW_INVALID_TRANSITION_THRESHOLD);
+  });
+
+  it("does not fire invalid-transition-loop below threshold", () => {
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [entry("2026-05-12T11:30:00.000Z", "Invalid transition: 'todo' → 'done'")],
+    }, { now });
+
+    expect(signal).toBeUndefined();
+  });
+
+  it("excludes older entries outside window", () => {
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [
+        entry("2026-05-12T09:00:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+        entry("2026-05-12T11:40:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+        entry("2026-05-12T11:50:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+      ],
+    }, { now, windowMs: STALLED_REVIEW_WINDOW_MS });
+
+    expect(signal).toBeUndefined();
+  });
+
+  it("returns undefined when not in-review", () => {
+    expect(detectStalledReview({ column: "todo", paused: false, log: [entry("2026-05-12T11:50:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN)] }, { now })).toBeUndefined();
+  });
+
+  it("returns undefined when paused", () => {
+    expect(detectStalledReview({ column: "in-review", paused: true, log: [entry("2026-05-12T11:50:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN)] }, { now })).toBeUndefined();
+  });
+
+  it("returns undefined when log is empty", () => {
+    expect(detectStalledReview({ column: "in-review", paused: false, log: [] }, { now })).toBeUndefined();
+  });
+
+  it("prioritizes reenqueue-churn when both heuristics match", () => {
+    const invalid = "Invalid transition: 'todo' → 'done'";
+    const signal = detectStalledReview({
+      column: "in-review",
+      paused: false,
+      log: [
+        entry("2026-05-12T11:30:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN, invalid),
+        entry("2026-05-12T11:40:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN, invalid),
+        entry("2026-05-12T11:50:00.000Z", STALLED_REVIEW_REENQUEUE_PATTERN),
+      ],
+    }, { now });
+
+    expect(signal?.heuristic).toBe("reenqueue-churn");
+  });
+});