Fix #5451 — refuse a MapFromAggregate VectorProjection registered Inline

[jeremydmiller]

Closes #5451. The diagnosis in the issue was right; this adds the measurement it said it lacked, then the refusal.

What an Inline registration actually did

The issue was written from reading the code, so I ran it before fixing it. Registering NoteAggregateVectorProjection (the existing MapFromAggregate test projection) Inline and reading content_text after each save:

	content_text	correct-if-async
after StartStream(NoteWritten("a body"))	no row at all	a body
after Append(NoteTitled("a title"))	a body	a title a body

Worse than "lags one change behind", strictly: the first save writes nothing, because live aggregation reads committed events and the stream has none yet, so the aggregate is null. Every later save then writes the state as of the previous event. The content hash records that stale text as current, and nothing fails.

The fix

ValidateConfiguration now refuses a non-Async registration when the map declares an aggregate type, following the lookup Fisher and Polecat already use: walk options.Projections.All, match IProjectionWrapper.InnerProjection by reference, read source.Lifecycle. It fires at DocumentStore.For(...) via AssertValidity, so this is a build-time failure, as the issue suggested.

Narrowed deliberately. Fisher and Polecat refuse every non-Async registration of their vector projections; Marten supports Inline for event-mapped projections on purpose — the class remarks call it "correct, not merely tolerated", since an event-mapped projection takes its text from the event it was handed and Inline has that in full. Only MapFromAggregate is unsound there, so only MapFromAggregate is refused.

Tests

• a_map_from_aggregate_projection_registered_inline_is_refused — asserts the message names both MapFromAggregate and ProjectionLifecycle.Async, so it points at the fix rather than just failing.
• the_same_projection_registered_async_still_builds
• an_event_mapped_projection_registered_inline_still_builds — the guard that matters most, since over-refusing would break a supported configuration.

Marten.PgVector.Tests on net9.0: 101 passed, 0 failed (98 before, plus these three). The existing map_from_aggregate_tests, registered Async, still passes — so the refusal does not over-fire.

One thing found on the way, not fixed here

ProjectionLifecycle.Live is also accepted silently for this projection. JasperFx's ProjectionGraph.Add already rejects Live for any plain IProjection ("Live cannot be used for IProjection"), but the overload Marten's opts.Projections.Add(projection, lifecycle) takes does not reach that guard. That is a gap in the registration path for every IProjection, not something specific to MapFromAggregate, so I left it alone rather than widening this fix to hide it. Happy to file it — say the word.

🤖 Generated with Claude Code

https://claude.ai/code/session_01481eiEZg1Bv6pu4DrgPRg3