Add note about validity in EBs

Author: ch1bo

docs/leios-design/README.md

@@ -614,10 +614,18 @@ In Praos, all transactions to be verified and applied to the ledger state are in
 
 - **REQ-LedgerResolvedBlockValidation** When validating a ranking block body, the ledger must be provided with all endorsed transactions resolved.
 - **REQ-LedgerUntickedEBValidation** When validating a ranking block body, the ledger must validate endorsed transactions against the ledger state before updating it with the new ranking block.
-- **REQ-LedgerTxValidationUnchanged** The actual transaction validation logic should remain unchanged, i.e., the ledger must validate each transaction as it does today.
+- **REQ-LedgerTxValidationUnchanged** The actual transaction validation logic should remain unchanged, i.e. the ledger must validate each transaction as it does today.
 
 The endorsement block itself does not contain any additional information besides a list of transaction identifiers (hashes of the full transaction bytes). Hence, the list of transactions is sufficient to reconstruct the EB body and verify the certificate contained in the RB. The actual transactions to be applied to the ledger state must be provided by the caller of the ledger interface, typically the storage layer.
 
+> ![NOTE]
+>
+> The EB actually contains transaction hashes + validity information. This is because block producers must be able to endorse / include transactions that fail phase-2 validation and consume collateral (thus be rewarded for this work without spending the input). This is consistent with what is stored in a Praos block today and the consensus/ledger interface should cover this already.
+
+> ![WARNING]
+>
+> TODO: update the EB CDDL in the CIP with this fact about the tx validity information
+
 ### Certificate verification
 
 In order to verify certificates contained in ranking blocks, the ledger must be aware of the voting committee and able to access their public keys. As defined by **REQ-RegisterBLSKeys**, SPOs must be able to register their BLS keys to become part of the voting committee. The ledger will need to be able to keep track of the registered keys and use them to do certificate verification. Besides verifying certificates, individual votes must also be verifiable by other components (e.g. to avoid diffusing invalid votes).