I found examples on how to type query results:

interface RootContextData{
    clientId:string;
    weightQuery:UseTRPCQueryResult<inferRouterOutputs<AppRouter>['children']['getWeight'], TRPCClientErrorLike<AppRouter>>,
    clientQuery:UseTRPCQueryResult<inferRouterOutputs<AppRouter>['clients']['getClient'], TRPCClientErrorLike<AppRouter>>,
}

But how to achieve the same for Mutations?
I figured it could be something like this:

{
   childrenAddWeightMutation:UseTRPCMutationResult<inferRouterOutputs<AppRouter>['children']['addWeight'], TRPCClientErrorLike<AppRouter>>
}

It asks for two more variables TVariables, TContext, not sure how to go about them.