This change means that we need to make two tests, right: one that handles the error being { BorshIoError: 'abc' } and a second test that handles it being "BorshIoError"?

I added it on line 54 as part of the generic test -- shouldn't that do what you're suggesting?

I dumb.

This is my lack of knowledge of how this is plumbed throughout the system -- if an old block contains { BorshIoError: "string" }, will that cause an issue? Or will it be properly parsed in the errors package?

I guess it, in fact, depends. Command clicking ‘show references’ on InstructionError eventually leads me to TransactionForAccountsMetaBase which exposes err: TransactionError (which contains InstructionError, sometimes).

I guess the thing that I don't know, is: after the change to the SDK, can RPC methods that return this type (eg. getBlock, blockSubscribe) return the newtype format anymore, or will they always return the unit type of BorshIoError?

v2 RPCs will always return the newtype, while v3 RPCs will always return the unit.

Yeah, this would require the thing that we don't have yet, which is the ability to build different Kit bundles based on the version of the RPC and/or enabled features (#28). Options are:

1. Scorched Earth, remove the old type, presume that all RPCs will be replace with v3 before anybody who would be affected upgrades to the next version of Kit
2. Keep both types, make a plan to eventually remove the old one when v3 is the network.

I figured in this particular case, option one would be fine, but you tell me – how long is it before v3 likely becomes the network?

v3 currently has the majority of stake (including frankendancer), so maybe scorched earth is ok:

Stake By Version:
3.1.0   -    6 current validators ( 0.15%)
3.0.8   -    1 current validators ( 0.01%)
3.0.7   -   65 current validators ( 4.20%)
3.0.6   -  359 current validators (38.31%)   5 delinquent validators ( 0.00%)
3.0.2   -    1 current validators ( 0.25%)
3.0.1   -    1 current validators ( 0.01%)
2.3.14  -    2 current validators ( 0.03%)
2.3.13  -   25 current validators ( 3.29%)   1 delinquent validators ( 0.02%)
2.3.11  -   63 current validators (16.21%)   2 delinquent validators ( 0.00%)
2.3.10  -   21 current validators ( 2.17%)
2.3.9   -    6 current validators ( 0.10%)   1 delinquent validators ( 0.00%)
2.3.8   -   98 current validators ( 8.51%)   8 delinquent validators ( 0.03%)
2.3.7   -    1 current validators ( 0.04%)
2.3.6   -   59 current validators ( 2.33%)   1 delinquent validators ( 0.00%)
2.3.5   -    2 current validators ( 0.40%)
0.712.30006 -  163 current validators (16.67%)
0.711.30006 -    2 current validators ( 0.19%)
0.709.30000 -    4 current validators ( 0.46%)
0.708.20306 -   50 current validators ( 6.39%)
0.707.20306 -    2 current validators ( 0.23%)
0.1.1   -    0 current validators ( 0.00%)   1 delinquent validators ( 0.00%)
unknown -    0 current validators ( 0.00%)  21 delinquent validators ( 0.01%)

OK. Let's do it. I need a stamp from you since I'm the last pusher.