By permanently deleting old workflows definition do you mean they you'd like to use back the same name?
If so, currently we do enforce unique names for all extension definitions, and this does include deleted definitions. As a workaround I can purge the old deleted definition so that it is actually removed from the database and your team can reuse the name.
The purge endpoint is internal only so if you'd like for me to purge it, do let me know your app id and extension definition id. Thank you!
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