ISS detector not getting all signatures

[lpetrovic05]

Problem

With multiple rounds per block (2 seconds of consensus time), we've found that the DefaultIssDetector will not process StateSignatureTransaction's for non-boundary rounds, so ISS's are essentially not detected. We will need to change something for this in the PlatformWiring or the DefaultIssDetector. For now we are going to change release/0.60 and main back to 1 round per block (through changing BlockStreamConfig::blockPeriod to 0, falls back to roundsPerBlock).For more context:The key issue is in the PlatformWiring.java file where the wiring is set up:\

1. The transactionHandlerStateAndRoundOutput is created with a filter that only passes StateAndRound objects with a non-null reservedSignedState:

   final OutputWire transactionHandlerStateAndRoundOutput = transactionHandlerWiring
   .getOutputWire()
   .buildFilter("notNullStateFilter", "state and round", ras -> ras.reservedSignedState() != null)
   .buildAdvancedTransformer(new StateAndRoundReserver("postHandler_stateAndRoundReserver"));

2. This filtered output is then passed through the StateHasher and eventually to the IssDetector:

hashedStateAndRoundOutputWire.solderTo(issDetectorWiring.getInputWire(IssDetector::handleStateAndRound));

3. The DefaultIssDetector.handleStateAndRound() method processes the system transactions from the StateAndRound object:

   issNotifications.addAll(handlePostconsensusSignatures(stateAndRound.systemTransactions()));

The problem is that only StateAndRound objects with a non-null reservedSignedState (which are only created for boundary rounds or freeze rounds) are passed to the IssDetector.This means:\

1. System transactions in non-boundary rounds are not directly passed to the IssDetector through the handleStateAndRound method.\
2. The IssDetector only sees system transactions from boundary rounds.This will lead to missed ISS detections if a boundary round doesn't contain the system transactions (StateSignatureTransaction) for an ISS round. Which will be almost always given a longer block period.

Proposed Solution

Change the output of the TransactionHandler to be RoutableData with two types of data: StateAndRound as it provides today, and Queue<ScopedSystemTransaction<StateSignatureTransaction>>. If the output is a StateAndRound object, it will be routed exactly as it is today. If it is a queue of signature transactions, it will be routed straight to the IssDetector. Thus, all signature transactions will be routed to the IssDetector either via the StateAndRound record or the queue.