Wire root layout provider stack and locale-scoped layout with i18n

Root layout wraps children with LoggerProvider, ApiClientProvider, and
ErrorBoundary. Locale layout validates lang param against 9 supported
languages and provides a request-scoped I18nProvider.

package.json

@@ -22,6 +22,7 @@
   },
   "dependencies": {
     "@modern-js/app-tools": "2.70.8",
+    "@modern-js/runtime": "^3.1.3",
     "@module-federation/enhanced": "2.3.2",
     "@module-federation/modern-js": "2.3.2",
     "@opentelemetry/api": "^1.9.1",

src/routes/[lang]/layout.tsx

@@ -0,0 +1,48 @@
+import { useState, useEffect, type ReactNode } from "react";
+import { useParams, useNavigate } from "@modern-js/runtime/router";
+import { isLanguage, type Language } from "@/i18n/resolver";
+import { createI18nInstance } from "@/i18n/config";
+import { I18nProvider } from "@/i18n/provider";
+import type i18next from "i18next";
+
+/**
+ * Locale-scoped layout. Validates the `lang` URL segment against the
+ * 9 supported languages, creates a request-scoped i18n instance, and
+ * wraps children with `<I18nProvider>`.
+ *
+ * Invalid `lang` values redirect to `/ru/` (default locale).
+ */
+export default function LangLayout({ children }: { children: ReactNode }): JSX.Element | null {
+  const params = useParams<{ lang: string }>();
+  const navigate = useNavigate();
+  const lang = params.lang ?? "";
+
+  const [i18n, setI18n] = useState<typeof i18next | null>(null);
+  const [validLang, setValidLang] = useState<Language | null>(null);
+
+  useEffect(() => {
+    if (!isLanguage(lang)) {
+      void navigate("/ru/", { replace: true });
+      return;
+    }
+
+    setValidLang(lang);
+
+    let cancelled = false;
+    void createI18nInstance({ locale: lang }).then((instance) => {
+      if (!cancelled) {
+        setI18n(instance);
+      }
+    });
+
+    return () => {
+      cancelled = true;
+    };
+  }, [lang, navigate]);
+
+  if (!validLang || !i18n) {
+    return null;
+  }
+
+  return <I18nProvider i18n={i18n}>{children}</I18nProvider>;
+}

src/routes/layout.tsx

@@ -1,5 +1,32 @@
 import type { ReactNode } from "react";
+import { ErrorBoundary } from "@/ui/errors/ErrorBoundary";
+import { LoggerProvider } from "@/observability/logger/provider";
+import { createRootLogger } from "@/observability/logger/root";
+import { ApiClientProvider } from "@/shared/api/provider";
+import { ApiClient } from "@/shared/api/client";
 
+const logger = createRootLogger();
+
+const apiClient = new ApiClient({
+  baseUrl: process.env["API_BASE_URL"] ?? "/api",
+  locale: "ru",
+  logger,
+});
+
+/**
+ * Root layout — wraps the entire app with global providers.
+ * Provider order (outermost to innermost):
+ *   LoggerProvider > ApiClientProvider > ErrorBoundary > children
+ *
+ * The locale-specific I18nProvider lives in src/routes/[lang]/layout.tsx
+ * so that each language segment gets its own i18n instance.
+ */
 export default function RootLayout({ children }: { children: ReactNode }): JSX.Element {
-  return <>{children}</>;
+  return (
+    <LoggerProvider logger={logger}>
+      <ApiClientProvider client={apiClient}>
+        <ErrorBoundary>{children}</ErrorBoundary>
+      </ApiClientProvider>
+    </LoggerProvider>
+  );
 }