Currently, the transaction code is part of the catalog_raii target in src/mongo/db/SConscript. We should evaluate whether it makes sense to keep the transaction code in catalog_raii in order to reduce the possibility of encountering circular dependencies in the future.

Initially, the transaction code used to live inside session.cpp but was refactored out into transaction_participant.cpp. There exists a dependency between TransactionParticipant and LockManager where we need to be able to know whether a read command is inside a transaction in order to decide whether to acquire a mode IS or mode IX lock. It would be helpful to investigate these dependencies in greater detail in order to prevent more tech debt.