The kernel or runtime selected message from the extension.
Callback to update runtime state from useRuntimeManager.
OptionalupdateStore: RuntimeSelectCallbackOptional callback to update editor-specific store.
OptionalsetKernelInitializing: KernelInitializingCallbackOptional callback to clear the initialization state.
Handles kernel-selected and runtime-selected messages by extracting the runtime, updating state, and managing spinner visibility per runtime type.