Errors and defects

class TransactionFailed {
  readonly message: string;
}
class PersistenceUnavailable {
  readonly message: string;
}

Two failures cross the boundary from a driver, and they are treated in opposite ways — because a caller can act on one and not on the other.

TransactionFailed — demoted to a defect

The atomicity machinery itself failing: a rejected commit, a savepoint that would not release.

By the time an effect reaches the unit of work, a repository has already translated its own constraint violations into domain errors. What is left is the boundary failing, which no use case can do anything about. withUnitOfWork calls Effect.die on it in this one place, which is what keeps a use case’s error channel as clean as its name — no catchTag for a condition whose only honest handler is a crash report.

UnitOfWork.run still types it, for the rare caller that wants it typed.

PersistenceUnavailable — propagates

The transient case: the store backing a repository is momentarily unable to service the request — connection lost, backend terminated.

It stays a typed failure because retrying is a real option and a transport boundary can turn it into a 503:

const caught =
  yield *
  placeOrder(input).pipe(
    Effect.catchTag("PersistenceUnavailable", () => HttpServerResponse.empty({ status: 503 })),
  );

It lives in this package, not in a host’s database package, so a module’s domain/ can name it in a repository port without importing infrastructure. Your adapter translates its own transient signal into this at the boundary.

It is distinct from a constraint violation, which is permanent: a repository either translates that into a domain error or lets it die as a defect.

The two wiring defects

Neither is a failure, because no call site declares them and none could handle them. Both are tagged, so a boot check or a test can name the condition instead of matching on a sentence.

EventDispatchedOutsideUnitOfWork — an event was dispatched with no boundary open. See After commit: the alternative is worse than a defect, since the events would buffer onto something nothing will ever drain.

DeferralWithoutEventBus — the sink’s defer was called with no EventBus in context, so there would be nothing to drain what it was handed. Only an EventBus should ever call it.

const defect = Result.getSuccess(Cause.findDefect(exit.cause));
Option.map(defect, (found) => found instanceof EventDispatchedOutsideUnitOfWork);

At a glance

Condition	Reaches a use case as	Why
TransactionFailed	a defect	nothing a caller can act on
PersistenceUnavailable	a typed failure	retry, or a 503, are real responses
EventDispatchedOutsideUnitOfWork	a defect	a forgotten boundary is a bug
DeferralWithoutEventBus	a defect	a wiring mistake in the sink’s caller

Type reference

Export	What it is
TransactionFailed	the boundary itself failed — demoted by the combinator
PersistenceUnavailable	transient store outage — propagates
EventDispatchedOutsideUnitOfWork	dispatched with no boundary open
DeferralWithoutEventBus	defer called with no bus in context