test(memory): cover shared batch output and error helpers

src/memory/batch-error-utils.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { extractBatchErrorMessage, formatUnavailableBatchError } from "./batch-error-utils.js";
+
+describe("extractBatchErrorMessage", () => {
+  it("returns the first top-level error message", () => {
+    expect(
+      extractBatchErrorMessage([
+        { response: { body: { error: { message: "nested" } } } },
+        { error: { message: "top-level" } },
+      ]),
+    ).toBe("nested");
+  });
+
+  it("falls back to nested response error message", () => {
+    expect(
+      extractBatchErrorMessage([{ response: { body: { error: { message: "nested-only" } } } }, {}]),
+    ).toBe("nested-only");
+  });
+});
+
+describe("formatUnavailableBatchError", () => {
+  it("formats errors and non-error values", () => {
+    expect(formatUnavailableBatchError(new Error("boom"))).toBe("error file unavailable: boom");
+    expect(formatUnavailableBatchError("unreachable")).toBe("error file unavailable: unreachable");
+  });
+});