Module agora.consensus.validation

We split validation in two separate phases: - Validation that does not require a 'context'; - Validation that does require a context;

We refer to context-less checks as 'syntax' checks, and context-using checks as 'semantic' checks (even though those terms are misnomers).

Elements (blocks, transactions) that are invalid without a context will always* be invalid for this version of the software. However it is possible a later upgrade will accept the element, or that they were previously accepted in an older version.

Elements that are invalid in a given context could become valid with a new, different context. An example is a transaction referencing a non-existing UTXO: the transaction could have not been broadcast yet, or could have not been reached the node yet.

Such a distinction is important to prevent denial of service, and to allow testing consensus rules under a different context, which is mandatory for our slasher implementation.