I also don’t see how the “unused gas” griefing vector described can’t also be done with an EOA transaction. Is there a better description of the attack somewhere that explains how it’s unique to user ops?
The issue of unused gas is only relevant for Type 4 Transactions because they can have their execution behaviour influenced by transactions that are coming after them in a block. This does not seem to be a problem unless the transaction suddenly starts using more gas than it used before.
Here is an example of how this could be turned into an attack on the block builder.
Here, Transaction #4 has a gas limit of 10’000’000. However, it only used 50’000 gas so there is a lot of available gas space in a block.
However, once Transaction #6 is included in a block and its validation phase flips some flag, Transaction #4 starts consuming the entire 10’000’000 gas.
