},
createSession: async (_client, params) => {
// Resolve fork turnId to a 0-based index using the source session's
// turn list in the state manager.
let fork: { session: URI; turnIndex: number; turnId: string } | undefined;
if (params.fork) {
const sourceState = this._stateManager.getSessionState(params.fork.session);
if (!sourceState) {