fix(config): coerce numeric meta.lastTouchedAt to ISO string

src/config/config.meta-timestamp-coercion.test.ts

@@ -0,0 +1,70 @@
+import { describe, expect, it, vi } from "vitest";
+
+describe("meta.lastTouchedAt numeric timestamp coercion", () => {
+  it("accepts a numeric Unix timestamp and coerces it to an ISO string", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const numericTimestamp = 1770394758161;
+    const res = validateConfigObject({
+      meta: {
+        lastTouchedAt: numericTimestamp,
+      },
+    });
+    expect(res.ok).toBe(true);
+    if (res.ok) {
+      expect(typeof res.config.meta?.lastTouchedAt).toBe("string");
+      expect(res.config.meta?.lastTouchedAt).toBe(new Date(numericTimestamp).toISOString());
+    }
+  });
+
+  it("still accepts a string ISO timestamp unchanged", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const isoTimestamp = "2026-02-07T01:39:18.161Z";
+    const res = validateConfigObject({
+      meta: {
+        lastTouchedAt: isoTimestamp,
+      },
+    });
+    expect(res.ok).toBe(true);
+    if (res.ok) {
+      expect(res.config.meta?.lastTouchedAt).toBe(isoTimestamp);
+    }
+  });
+
+  it("rejects out-of-range numeric timestamps without throwing", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const res = validateConfigObject({
+      meta: {
+        lastTouchedAt: 1e20,
+      },
+    });
+    expect(res.ok).toBe(false);
+  });
+
+  it("passes non-date strings through unchanged (backwards-compatible)", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const res = validateConfigObject({
+      meta: {
+        lastTouchedAt: "not-a-date",
+      },
+    });
+    expect(res.ok).toBe(true);
+    if (res.ok) {
+      expect(res.config.meta?.lastTouchedAt).toBe("not-a-date");
+    }
+  });
+
+  it("accepts meta with only lastTouchedVersion (no lastTouchedAt)", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const res = validateConfigObject({
+      meta: {
+        lastTouchedVersion: "2026.2.6",
+      },
+    });
+    expect(res.ok).toBe(true);
+  });
+});