P95:

“But, whether you click the edit link for the first product on the list or point your browser at the edit route for that product, the ProductLive.Index live view will call handle_params/3.”

It is not clear, from this and the related explanations above, under which circumstances mount is called. Here you say it will call handle_params (although you don’t say anything about mount). Above, you say that pointing your browser at edit will call mount without handle_params.