diff --git a/csv-table-hub-main/src/__tests__/session.test.ts b/csv-table-hub-main/src/__tests__/session.test.ts
index d5fbecd..6037403 100644
--- a/csv-table-hub-main/src/__tests__/session.test.ts
+++ b/csv-table-hub-main/src/__tests__/session.test.ts
@@ -130,7 +130,10 @@ describe("requireSession (route guard)", () => {
       thrown = e;
     }
     expect(isRedirect(thrown)).toBe(true);
-    expect((thrown as { options: { to: string } }).options.to).toBe("/auth");
+    const { options } = thrown as { options: { to: string; reloadDocument?: boolean } };
+    expect(options.to).toBe("/auth");
+    // #133: a client-side redirect during hydration crashed the router (React #520/#422).
+    expect(options.reloadDocument).toBe(true);
   });
 
   it("lets a signed-in user through", () => {
diff --git a/csv-table-hub-main/src/lib/session.ts b/csv-table-hub-main/src/lib/session.ts
index 3fd75a9..a791a38 100644
--- a/csv-table-hub-main/src/lib/session.ts
+++ b/csv-table-hub-main/src/lib/session.ts
@@ -98,9 +98,11 @@ export function authHeaders(): Record<string, string> {
   return s ? { Authorization: `Bearer ${s.token}` } : {};
 }
 
-/** Route guard (#96): send anyone without a live session to the sign-in page. */
+/** Route guard (#96): send anyone without a live session to the sign-in page.
+ *  A full page load, not a client-side redirect: redirecting while the first
+ *  page hydrates broke the router's match tree (React #520/#422, #133). */
 export function requireSession(): void {
-  if (!getSession()) throw redirect({ to: "/auth" });
+  if (!getSession()) throw redirect({ to: "/auth", reloadDocument: true });
 }
 
 /** Change your own password (#117). This session stays; the server ends all others. */