feat: add sender profile cache with LRU eviction

- SenderNameCache: TTL 10min, LRU max 2048 entries, getOrFetch pattern
- resolveSenderName: API call with cache integration
- Trigger uses cache for approval card resolutions and audit metadata
- Add unit tests (9) for cache lifecycle, LRU, expiry, and null handling

hub/test/unit/sender-cache.test.ts

@@ -0,0 +1,107 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { SenderNameCache } from "../../src/feishu/senderCache.js";
+
+describe("SenderNameCache", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("get returns null for missing key", () => {
+    const cache = new SenderNameCache();
+
+    expect(cache.get("ou_user")).toBeNull();
+  });
+
+  it("set then get returns the name", () => {
+    const cache = new SenderNameCache();
+
+    cache.set("ou_user", "Alice");
+
+    expect(cache.get("ou_user")).toBe("Alice");
+  });
+
+  it("expired entry returns null", () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-01-01T00:00:00Z"));
+    const cache = new SenderNameCache({ ttlMs: 100 });
+
+    cache.set("ou_user", "Alice");
+    vi.advanceTimersByTime(101);
+
+    expect(cache.get("ou_user")).toBeNull();
+    expect(cache.size()).toBe(0);
+  });
+
+  it("getOrFetch uses cache on hit", async () => {
+    const cache = new SenderNameCache();
+    const fetchFn = vi.fn(async () => "Fetched Alice");
+    cache.set("ou_user", "Alice");
+
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBe("Alice");
+
+    expect(fetchFn).not.toHaveBeenCalled();
+  });
+
+  it("getOrFetch calls fetchFn on miss", async () => {
+    const cache = new SenderNameCache();
+    const fetchFn = vi.fn(async () => "Alice");
+
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBe("Alice");
+
+    expect(fetchFn).toHaveBeenCalledTimes(1);
+    expect(fetchFn).toHaveBeenCalledWith("ou_user");
+  });
+
+  it("getOrFetch caches the result of fetchFn", async () => {
+    const cache = new SenderNameCache();
+    const fetchFn = vi.fn(async () => "Alice");
+
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBe("Alice");
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBe("Alice");
+
+    expect(fetchFn).toHaveBeenCalledTimes(1);
+  });
+
+  it("evicts the least recently used entry when full", () => {
+    const cache = new SenderNameCache({ maxSize: 2 });
+
+    cache.set("ou_1", "Alice");
+    cache.set("ou_2", "Bob");
+    expect(cache.get("ou_1")).toBe("Alice");
+    cache.set("ou_3", "Carol");
+
+    expect(cache.get("ou_1")).toBe("Alice");
+    expect(cache.get("ou_2")).toBeNull();
+    expect(cache.get("ou_3")).toBe("Carol");
+  });
+
+  it("clear empties the cache", () => {
+    const cache = new SenderNameCache();
+
+    cache.set("ou_user", "Alice");
+    cache.clear();
+
+    expect(cache.get("ou_user")).toBeNull();
+    expect(cache.size()).toBe(0);
+  });
+
+  it("size returns correct count", () => {
+    const cache = new SenderNameCache();
+
+    cache.set("ou_1", "Alice");
+    cache.set("ou_2", "Bob");
+
+    expect(cache.size()).toBe(2);
+  });
+
+  it("getOrFetch with null fetchFn result does not cache null", async () => {
+    const cache = new SenderNameCache();
+    const fetchFn = vi.fn(async () => null);
+
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBeNull();
+    await expect(cache.getOrFetch("ou_user", fetchFn)).resolves.toBeNull();
+
+    expect(fetchFn).toHaveBeenCalledTimes(2);
+    expect(cache.size()).toBe(0);
+  });
+});