fix(core): recover v2 context overflow (#31005)

packages/llm/src/index.ts

@@ -1,6 +1,7 @@
 export { LLMClient } from "./route/client"
 export { Auth } from "./route/auth"
 export { Provider } from "./provider"
+export { isContextOverflow, isContextOverflowFailure } from "./provider-error"
 export type {
   RouteModelInput,
   RouteRoutedModelInput,