It would be beneficial to have the CDI-specific wrapper around Narayana's TransactionManagerImple that fires an @Initialized(TransactionScoped.class)-qualified event.

For the CDI, it's a good practice. The all built-in scopes have to provide this behaviour.

The CDI specification says (in section 6.7):

Portable extensions are encouraged to synchronously fire:

• an event with qualifier @Initialized(X.class) when a custom context is initialized, i.e. ready for use,
• an event with qualifier @BeforeDestroyed(X.class) when a custom context is about to be destroyed, i.e. before the actual destruction,
• an event with qualifier @Destroyed(X.class) when a custom context is destroyed, i.e. after the actual destruction,

where X is the scope type associated with the context.

A suitable event payload should be chosen.

The begin() method a Narayana-supplied but CDI-specific transaction manager wrapping Narayana's "ordinary" one should do:

@Inject
@Initialized(TransactionScoped.class)
private Event<Transaction> initializationBroadcaster;

@Inject @BeforeDestroyed(TransactionScoped.class)
private Event<Transaction> beforeDestructionBroadcaster;

@Inject @Destroyed(TransactionScoped.class)
private Event<TransactionManager> destructionBroadcaster;

// in its begin() method:
super.begin();
initializationBroadcaster.fire(this.getTransaction());

// in its commit() and rollback() methods and anywhere else I'm forgetting: 
beforeDestructionBroadcaster.fire(this.getTransaction());
super.commit(); // or rollback or whatever
destructionBroadcaster.fire(this);