refactor(i18n): share error message maps between web and native

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/i18n/test/errors.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, test, vi } from "vitest";
+
+vi.mock("../src/index", () => ({
+  i18n: {
+    locale: "en",
+    _: (descriptor: { id?: string; message?: string } | string) => {
+      if (typeof descriptor === "string") return descriptor;
+      return descriptor.message ?? descriptor.id ?? "";
+    },
+  },
+}));
+
+vi.mock("@lingui/core/macro", () => ({
+  msg: (strings: TemplateStringsArray, ...values: unknown[]) => ({
+    id: String.raw(strings, ...values),
+    message: String.raw(strings, ...values),
+  }),
+}));
+
+import { getAppErrorCode, getAuthErrorMessage, getErrorMessage } from "../src/errors";
+
+describe("getAppErrorCode", () => {
+  test("recognizes a plain object carrying an app error code", () => {
+    expect(getAppErrorCode({ data: { code: "JOB_NOT_FOUND" } })).toBe("JOB_NOT_FOUND");
+  });
+
+  test.each([["oops"], [null], [{}], [{ data: { code: 5 } }]])("returns null for %j", (input) => {
+    expect(getAppErrorCode(input)).toBeNull();
+  });
+});
+
+describe("getErrorMessage", () => {
+  test("returns the English message for a mapped code", () => {
+    expect(getErrorMessage({ data: { code: "JOB_NOT_FOUND" } })).toBe("Job not found");
+  });
+
+  test("falls back to the given fallback for an unknown code", () => {
+    expect(getErrorMessage({ data: { code: "NOPE" } }, "Fallback")).toBe("Fallback");
+  });
+});
+
+describe("getAuthErrorMessage", () => {
+  test("maps a 429 status to the rate-limit message", () => {
+    expect(getAuthErrorMessage({ status: 429 }, "F")).toMatch(/^Too many attempts/);
+  });
+
+  test("maps a known auth code and falls back otherwise", () => {
+    expect(getAuthErrorMessage({ code: "INVALID_EMAIL" }, "F")).toBe("Enter a valid email address");
+    expect(getAuthErrorMessage({ code: "UNKNOWN" }, "F")).toBe("F");
+  });
+});