Conway support

[ch1bo]

Why

Users should be able to keep their Hydra heads open across a hard-fork.

On a Cardano network hard-fork event, it will forge blocks of a different era. Unless the hydra-node is updated to understand also these blocks, they will not be understood and the Hydra protocol transactions cannot be observed.

The next event will be the fork into Conway era in Q1 or Q2 2024.

What

• The hydra-node does detect and inform users when era of a network is not supported.

  • It may crash in doing so.
  • This may be released in a version not yet supporting Conway.

• A new version of the hydra-node is created which understands Conway blocks.

  • All hydra protocol transactions can be observed from both Babbage an Conway transactions.

  • The hydra-node and its layer 2 ledger does still understand Babbage transactions.

  • Optional: Does understand Conway transactions and is backwards compatible.

• Users can switch to this new version of hydra-node to "regain" access to a head.

  • No breaking changes or migration paths exist (e.g. removing a file)
  • It is possible to make a hydra-node compatible with a new era while using the same hydra scripts version (= same script hashes)
  • We want to be able (ourselves) to have a head open before the hard-fork and close it after the hard-fork (with the same or an updated hydra-node version) -> demo in the monthly

How

• [x] #1216
• [x] Check whether babbage transactions can still be processed by a Conway ledger
  • to be compatible with L1 before/after hardfork and as our L2
• [x] #1227
  • Change chain sync to decode Conway transactions, but still construct Babbage transactions, so it works before/after hard-fork.
• [ ] Maybe not: Switch era used in L2 (depends on step above)
• [ ] Bonus: Check whether #1193 is still present when using the same ledger version as the cardano-node

TBD

• How much of "not be forced to change script hashes" is in scope?

  • [ ] Separate hydra-plutus toolchain from hydra-node to not be forced to update the plutus-tx compiler when updating the ledger dependency in hydra-node.
  • [x] Do a release with cardano-ledger/plutus versions supporting Conway already before the hard-fork (but hydra-node not yet) and pray that no breaking bumps are needed.

• Is supporting the current and next era enough on the chain sync side?

• Are all ledger changes backward compatible? i.e. will we always be able to submit old era txs?

  • [x] Ledger team: From Shelley onward, the wire format for transactions has been backward compatible. We would have to have a very strong reason to abandon this commitment.

• With backward compatible transaction formats, there is no breaking change on L2

[locallycompact]

Moving to cardano-node 8.7.2 as a first step. https://github.com/input-output-hk/hydra/pull/1199

[ffakenz]

Adding support in IsXEraOnwards type classes as a second step. #1207

[ffakenz]

Adding report error on "unsupported era" as next step. #1219

[ffakenz]

Adding support to survive an era fork as a next step. #1227