How to read Attachment by advanced scripting during the first transition "create"

[Laith Ata]

I have the following problem:

I copy an issue with attachment into a new issue and I wish to be able to read the attachment by the first transition "create", which means before the first status (Create Issue / Open / ...) is set.
I tried many approaches (related to attachment as found in Jira forums such as https://community.atlassian.com/t5/Answers-Developer-Questions/How-to-read-Attachments-from-the-Create-Issue-Page/qaq-p/468020 )

I understand from my readings (on the forums) that the attachment are not yet completely available by that first transition, but it is possible to access some equivalent temporary attachment.
However all my attempts have failed.

Any ideas how to do get the attachment in the temporary directory? Code snippets, pointers? Thank you.