I thought to have a good understanding of global hash cookie but no

In my case (see attach), I have a B&E form and in the edit from an another B&E form launched in a iframe via a run object.
Ideally, I should had created a subform instead of a run/iframe but I have a join and then edition does not work.
Anyway, I have got the "record_id" (in the hash()) till the BE step but I need it for saving he new record and then of course, it is not the "parent record_id" but the current.
I have tried the nuSetProperty( 'id', record_id.value, true) as you have suggested previously in the JS of the custom code of the form and it does not work

So, shortly, how can I get the record_id (hash) I have in the BE step to the BS or AS step ?
Thanks a lot in advance