The default pipeline no longer seats middleware

What changed. AddDispatch() used to seat four middleware on the default pipeline profile: TenantIdentityMiddleware, TimeoutMiddleware, MetricsLoggingMiddleware and OutboxStagingMiddleware. The default profile is now empty. A host that configures nothing dispatches and does nothing else.

All four are still registered by AddDispatch(), so naming any of them on a pipeline resolves without extra work. What changed is what runs by default, not what is available.

Do I need to do anything?

Almost certainly not, and the one population that does is narrow. Check yourself against this before reading further:

if your host…	then
calls UseOutbox()	unaffected. UseOutbox() seats the staging stage itself and always did
has no IOutboxStore registered	unaffected. A handler writing to the outbox already threw before this change — the middleware skipped itself when no store was present and the writer threw on the missing context
registers an IOutboxStore but never calls UseOutbox()	this is the one. Action required — see below
relies on the default timeout	name TimeoutMiddleware, or handle timeouts yourself
relies on tenant identity being resolved for every message	name TenantIdentityMiddleware
relies on the default metrics logging	name MetricsLoggingMiddleware

If you register a store but never call UseOutbox()

You are affected because we told you that was enough. The previous version's own error text said:

"Outbox staging runs on the default pipeline automatically once a store is present, so no further pipeline configuration is needed."

That is no longer true, and it is the contract this change breaks. Add the stage:

services.AddDispatch(builder => builder.UseOutbox());

UseOutbox() also registers a startup check that fails fast if the store is missing, which is why it is the call to reach for. If you want only the stage, pipeline.Use<OutboxStagingMiddleware>() does that and nothing else.

You will not lose a write silently. A handler that writes to the outbox on a pipeline with no staging stage throws at dispatch, and the message names both halves — the IOutboxStore registration and the stage.

Restoring the previous behaviour

services.AddDispatch(builder => builder.ConfigurePipeline("Default", pipeline => pipeline
    .ForMessageKinds(MessageKinds.All)
    .Use<TenantIdentityMiddleware>()
    .Use<TimeoutMiddleware>()
    .Use<MetricsLoggingMiddleware>()
    .Use<OutboxStagingMiddleware>()));

Or name only the ones you actually use — which is the point of the change.

Why

Two reasons, and the second is the one that mattered.

Cost. Measured on the warm path, against the same benchmark used for the published comparison figures, with three of your own middleware in the pipeline:

default profile	per dispatch
four middleware (before)	1,836 ns / 1,960 B
one semantically-inert middleware	419 ns / 688 B
empty (now)	71.5 ns / 240 B

Those four cost roughly 25x the entire remaining cost of a dispatch, on hosts that had asked for none of them. Note the middle row: even a single stage that does nothing when its capability is absent — outbox staging without a store — costs +346 ns and +448 B per dispatch. Semantically inert is not free, and that measurement is what removed the last candidate for a default.

Behaviour. Cost alone would not have justified a breaking change. Two of the four changed what your code does. TimeoutMiddleware can cancel a handler on a deadline you never chose. TenantIdentityMiddleware resolves a tenant identity for a host that never asked to be multi-tenant. Behaviour that arrives because you called a registration method is behaviour you cannot find by reading your own code, and cannot remove without knowing it is there.

This brings the framework in line with how ASP.NET Core treats the same problem: a registration call seats infrastructure, and behaviour is something you add. AddAuthorization() does not authorize anything; you add the middleware.

When

Pre-RC. The API is frozen at 10.0.0-rc.1, so this lands before then; after 10.0.0 a change of this shape is reserved for a new major line.