Always use transaction extensions version 0 when working with v4 transactions, and find latest match when using v5 #1998
Description
v4 transactions should always be encoded or decoded using the transaciton extensions under version 0 in the metadata. Currently, they would use the latest available version (which is ok at the moment because there only exists one version anyway; 0).
This is more complicated than just setting which version we'll look at, because V4 and V5 transactions will differ in their behaviour.
- V4 transactions should always use version 0
- V5 transactions should tend to using the latest version, but really should look for the version that lines up with the configured transaction extensions for the chain, and use that.
- In the event that there is a version change, but the transaction extension names remain identical (only the properties of one or more of them change), we would have a dilemma as to which version to select. Thus, perhaps we should allow the user to explicitly configure which version of extensions to try to use, falling back to a sane default (use the latest that matches?) otherwise. Names changing would be an issue though and so I would expect that this wouldn't happen, so we can probably just be clever and pick the latest matching set.