IS there a script that will allow me to automatically copy an attachment from the subtask to the parent when the attachment is uploaded to the subtask?
While I'm not sure about a means to do this when the attachment is uploaded, I did find another users script to do this same task in a post function. Please see https://community.atlassian.com/t5/Answers-Developer-Questions/Scripted-post-function-copy-attachment/qaq-p/498490 for more details.
While that user posted their initial non-working script, it looks like he got some help from @Thanos Batagiannis _Adaptavist_ in regards to what packages could be used to make that work. Perhaps this would help for your use case as well.
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