chore: import upstream snapshot with attribution

test/reranker.test.ts

@@ -0,0 +1,62 @@
+import { describe, it, expect, vi } from "vitest";
+
+vi.mock("@xenova/transformers", () => {
+  throw new Error("not installed");
+});
+
+import { rerank, isRerankerAvailable } from "../src/state/reranker.js";
+
+describe("reranker", () => {
+  it("returns results unchanged when @xenova/transformers is unavailable", async () => {
+    const results = [
+      {
+        observation: {
+          id: "o1",
+          title: "First",
+          narrative: "First result",
+        },
+        bm25Score: 0.5,
+        vectorScore: 0.6,
+        graphScore: 0,
+        combinedScore: 0.8,
+        sessionId: "s1",
+      },
+      {
+        observation: {
+          id: "o2",
+          title: "Second",
+          narrative: "Second result",
+        },
+        bm25Score: 0.3,
+        vectorScore: 0.4,
+        graphScore: 0,
+        combinedScore: 0.5,
+        sessionId: "s1",
+      },
+    ] as any;
+
+    const reranked = await rerank("test query", results);
+    expect(reranked).toEqual(results);
+  });
+
+  it("isRerankerAvailable returns false when not loaded", () => {
+    expect(isRerankerAvailable()).toBe(false);
+  });
+
+  it("handles single result gracefully", async () => {
+    const results = [
+      {
+        observation: { id: "o1", title: "Only" },
+        combinedScore: 1.0,
+      },
+    ] as any;
+
+    const reranked = await rerank("query", results);
+    expect(reranked).toHaveLength(1);
+  });
+
+  it("handles empty results", async () => {
+    const reranked = await rerank("query", []);
+    expect(reranked).toHaveLength(0);
+  });
+});