title_body: What decisions are left to the slot leader? Is the order of transactions deterministic, or is it decided by the slot leader when creating the block?  Are DEX front-running attacks a possibility?
  Can the slot leader censor specific transactions or computations (delay them for that 20-second slot)?  If there is congestion, how are the slot's resources rationed?
  
  These are a couple examples I came up with, but I'm generally wondering what kinds of choices the slot leader is empowered to make. (in order to consider how those opportunities might be abused in subtle ways)
upvoted_answer: The Haskell reference implementation of the Cardano node, leaves no such decisions to the slot leader, and most (if not all) are using that node implementation.
  As far as the Cardano protocol is concerned, however, the slot leader could cherry pick transactions and for example prefer those with higher fees.