deleting files after syncing them

I am using syncing to move files between 2 systems (a->b) then after some processing, deleting the files on b.

I see in the transfer queue the files syncing a>b and a queue of files to delete a<b. when does syncthing delete the waiting files? does it wait till the a>b transfers finish or are they intermixed?

“B” will first sync the files in its queue, then process local changes (deletes). So the precise order will depend on the particulars of how long the queue was etc., best not depend on a specific behavior here – consider it intermixed with arbitrary delay.