Add auth expiry interceptor and session-expired redirect

frontend/src/utils/__tests__/fetchError.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it, vi } from "vitest";
+import { ApiError } from "../../api/client";
+import { handleFetchError } from "../fetchError";
+
+describe("utils/fetchError", () => {
+  it("ignores AbortError errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new DOMException("Aborted", "AbortError"), setError, "fallback");
+    expect(setError).not.toHaveBeenCalled();
+  });
+
+  it("ignores auth errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new ApiError(401, "Unauthorized"), setError, "fallback");
+    expect(setError).not.toHaveBeenCalled();
+  });
+
+  it("sets fallback for normal errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new Error("Oops"), setError, "fallback");
+    expect(setError).toHaveBeenCalledWith("Oops");
+  });
+});

frontend/src/utils/fetchError.ts

@@ -1,3 +1,5 @@
+import { isAuthError } from "../api/client";
+
 /**
  * Normalize fetch error handling across hooks.
  */
@@ -10,5 +12,9 @@ export function handleFetchError(
     return;
   }
 
+  if (isAuthError(err)) {
+    return;
+  }
+
   setError(err instanceof Error ? err.message : fallback);
 }