chore: import upstream snapshot with attribution

showcase/shell-docs/src/app/[[...slug]]/error.tsx

@@ -0,0 +1,48 @@
+"use client";
+
+import { useEffect } from "react";
+import { usePathname } from "next/navigation";
+
+export default function DocsError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  const pathname = usePathname();
+  useEffect(() => {
+    // Log the full Error instance (not just .message/.digest) so the
+    // stack trace reaches the server log / browser devtools. Include
+    // pathname where available so reports can be tied back to a page.
+    console.error(
+      `[docs] Page render error${pathname ? ` on ${pathname}` : ""}:`,
+      error,
+    );
+  }, [error, pathname]);
+
+  return (
+    <div className="flex items-center justify-center min-h-[50vh]">
+      <div className="text-center max-w-md">
+        <h2 className="text-lg font-semibold text-[var(--text)] mb-2">
+          Something went wrong
+        </h2>
+        <p className="text-sm text-[var(--text-muted)] mb-4">
+          We hit an error rendering this page. Please refresh, and if it keeps
+          happening, report it with the ID below so we can track it down.
+        </p>
+        {error.digest && (
+          <p className="text-xs text-[var(--text-faint)] mb-4 font-mono">
+            Error ID: {error.digest}
+          </p>
+        )}
+        <button
+          onClick={reset}
+          className="shell-docs-radius-control h-10 border border-[var(--border)] px-4 text-sm text-[var(--text-secondary)] transition-colors hover:bg-[var(--bg-elevated)]"
+        >
+          Try again
+        </button>
+      </div>
+    </div>
+  );
+}