fix(agent): improve time awareness with timestamped turns

src/agent/message-timestamp.test.ts

@@ -0,0 +1,57 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { injectMessageTimestamp, resolveMessageTimezone } from "./message-timestamp.js";
+
+describe("injectMessageTimestamp", () => {
+  const originalTz = process.env.TZ;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-01-29T01:30:00.000Z"));
+    process.env.TZ = "America/New_York";
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    process.env.TZ = originalTz;
+  });
+
+  it("prepends a compact timestamp prefix", () => {
+    const result = injectMessageTimestamp("Is it the weekend?");
+    expect(result).toMatch(/^\[Wed 2026-01-28 20:30 EST\] Is it the weekend\?$/);
+  });
+
+  it("does not double-stamp already enveloped messages", () => {
+    const existing = "[Wed 2026-01-28 20:30 EST] hello";
+    expect(injectMessageTimestamp(existing)).toBe(existing);
+  });
+
+  it("does not stamp cron messages that already include current time lines", () => {
+    const existing = "Cron run\nCurrent time: Wednesday, January 28th, 2026 — 8:30 PM (America/New_York)";
+    expect(injectMessageTimestamp(existing)).toBe(existing);
+  });
+
+  it("returns empty/whitespace input unchanged", () => {
+    expect(injectMessageTimestamp("")).toBe("");
+    expect(injectMessageTimestamp("   ")).toBe("   ");
+  });
+});
+
+describe("resolveMessageTimezone", () => {
+  const originalTz = process.env.TZ;
+
+  afterEach(() => {
+    process.env.TZ = originalTz;
+  });
+
+  it("prefers explicit argument when valid", () => {
+    process.env.TZ = "UTC";
+    expect(resolveMessageTimezone("America/Chicago")).toBe("America/Chicago");
+  });
+
+  it("falls back to UTC for invalid values", () => {
+    process.env.TZ = "Invalid/Timezone";
+    const resolved = resolveMessageTimezone("also/invalid");
+    expect(resolved).not.toBe("Invalid/Timezone");
+    expect(resolved.length).toBeGreaterThan(0);
+  });
+});