feat(auth): force re-auth on failed refresh

requireAuth() now redirects on user.error so SSR catches stale sessions
that the cookie-presence middleware can't see. New SessionExpirationGuard
(client) listens on useSession() and calls signIn("keycloak") when the
JWT carries RefreshAccessTokenError or RefreshTokenMissing. Without it,
a tab idle past the Keycloak SSO lifetime sat on a dead accessToken
until a downstream API 401'd, with no UI-level redirect.

Bumps to 0.4.1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/auth/SessionExpirationGuard.tsx

@@ -0,0 +1,50 @@
+"use client";
+
+import { useEffect, useRef } from "react";
+import { useSession, signIn } from "next-auth/react";
+
+import type { SessionUser } from "./types";
+
+/**
+ * Drop-in client component that re-triggers Keycloak sign-in when the
+ * kit's server-side refresh flow gives up (`session.user.error` set to
+ * `RefreshAccessTokenError` or `RefreshTokenMissing`).
+ *
+ * Without this, a UI tab left open past the Keycloak SSO session lifetime
+ * holds a stale `accessToken`: the middleware sees a cookie, `requireAuth`
+ * sees an `accessToken` string, and the user only finds out things are
+ * broken when a downstream API returns 401. Mount this inside a
+ * `<SessionProvider>` (typically alongside other providers in the locale
+ * root) so the session refetch interval surfaces the error within minutes.
+ *
+ * Renders nothing.
+ */
+export function SessionExpirationGuard() {
+  const { data: session } = useSession();
+  const error = (session?.user as Partial<SessionUser> | undefined)?.error;
+  // Guard against React's StrictMode double-invoke + the brief window
+  // between calling signIn and the page navigating away.
+  const firedRef = useRef(false);
+
+  useEffect(() => {
+    if (!error || firedRef.current) return;
+    if (
+      error !== "RefreshAccessTokenError" &&
+      error !== "RefreshTokenMissing"
+    ) {
+      return;
+    }
+    firedRef.current = true;
+    const callbackUrl =
+      typeof window !== "undefined"
+        ? window.location.pathname + window.location.search
+        : "/";
+    // signIn() POSTs the CSRF-protected provider endpoint, which then
+    // initiates a fresh OIDC flow; the stale session cookie is replaced
+    // atomically when the flow completes. Keycloak's own SSO cookie may
+    // still log the user in transparently if it hasn't also expired.
+    void signIn("keycloak", { callbackUrl });
+  }, [error]);
+
+  return null;
+}