Currently a transaction participant will get the highest txnNumber the SessionCatalog has seen for any transaction in the current logical session when refreshing the participant from disk. This is to avoid reading more config.transactions entries than necessary. This is gotten from the SessionRuntimeInfo of the participant's session from the SessionCatalog. By this point, the participant has already checked out the session once, so we should be able to avoid looking back into the SessionCatalog (and locking its mutex) by caching the highest seen txnNumber onto the participant's Session, which is accessible directly in the transaction participant code.