Make container-scoped projections usable by live aggregation and validate them

[jeremydmiller]

Fixes the JasperFx.Events half of JasperFx/marten#5095. The Marten side is JasperFx/marten#5134.

The two bugs

A projection registered through AddProjectionWithServices with a Scoped or Transient lifetime is wrapped in ScopedAggregationWrapper. Two things follow from that wrapper:

1. Native aggregation silently ignores the projection. The wrapper does not implement IAggregatorSource<TQuerySession>, so ProjectionGraph.AggregatorFor<T>() never finds it — the lookup falls through tryFindProjectionSourceForAggregateType to conventional aggregation built off the aggregate type itself. AggregateStreamAsync, RebuildSingleStreamAsync, and AggregateToAsync therefore run something other than the registered projection, with no error. Registering the same projection as a Singleton works, because single stream projections implement IAggregatorSource directly.

2. Validation is skipped. ProjectionSourceWrapperBase's constructor copies name/version/options off the resolved source but never calls AssembleAndAssertValidity() on it. Only the wrapper gets validated, so a projection that a Singleton registration rejects at startup is silently accepted when registered Scoped — and switching to Singleton later surfaces a configuration error that had been hidden all along.

The fix

ScopedSingleStreamAggregationWrapper adds IAggregatorSource on top of the general aggregation wrapper.

This is a separate type rather than something the base wrapper does for every aggregation projection, and that's the main design call here: only JasperFxSingleStreamProjectionBase implements IAggregator. Making the base wrapper an IAggregatorSource would newly expose multi-stream projections to AggregatorFor — which the Singleton path does not do — and their Build<T>() would fail an invalid cast at runtime. Splitting the type keeps scoped and singleton behavior identical for both projection shapes.

ScopedAggregator resolves the projection from a fresh container scope on every aggregation call and delegates. It deliberately holds no projection instance: the whole point of choosing Scoped/Transient is that the projection and its dependency graph are not safe to cache, and AggregatorFor caches the aggregator itself for the life of the store. Caching a resolved projection there would reintroduce exactly the singleton-safety problem the user was avoiding.

ProjectionSourceWrapperBase now calls AssembleAndAssertValidity() on the resolved source. That constructor is the one choke point every scoped wrapper passes through, including composite children.

Because that constructor runs through reflection, a validation failure would surface as TargetInvocationException. The new static ScopedAggregationWrapper.Build selector unwraps it via ExceptionDispatchInfo so callers see the real InvalidProjectionException with its original stack. Build also picks the right wrapper for the projection shape, so event stores call one helper instead of closing a wrapper type directly.

Verification

Everything was proven through Marten against a local pack of this branch, since the behavior is only observable through a real store.

The repro is a 3×3 matrix — {live aggregation, single stream rebuild, invalid-projection validation} × {Singleton, Scoped, Transient} — using an aggregate with no conventional Create/Apply methods, so the conventional fallback cannot accidentally produce a correct-looking answer.

	before	after
Repro matrix	3 passed / 6 failed	9 passed

Every failure was Scoped or Transient; every Singleton case passed throughout, which is exactly the asymmetry the issue reports.

No regressions: JasperFx EventTests 672/672; Marten ContainerScopedProjectionTests 80/80, EventSourcingTests 1614/1614, DaemonTests 267/267, full Marten.slnx builds clean.

Note for Polecat

ScopedAggregationWrapper.Build is the entry point to adopt — an event store that closes the wrapper type directly still gets the validation fix (it is in the shared base constructor) but not the aggregator fix.

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