Materialize EF domain-event scraper before publishing (#2585)

[jeremydmiller]

Fixes #2585.

The bug

DomainEventScraper<T,TEvent>.ScrapeEvents enumerated this LINQ pipeline lazily and then await bus.PublishAsync(...) per event inside the foreach:

var eventMessages = dbContext.ChangeTracker.Entries().Select(x => x.Entity)
    .OfType<T>().SelectMany(_source);

foreach (var eventMessage in eventMessages)
{
    await bus.PublishAsync(eventMessage);
}

With the EF-backed outbox, PublishAsync flows through EfCoreEnvelopeTransaction.PersistIncomingAsync, which adds an IncomingMessage entity to the same DbContext. That mutates the ChangeTracker mid-enumeration and throws:

InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at Wolverine.EntityFrameworkCore.DomainEventScraper`2.ScrapeEvents

The fix

.ToArray() at the end of the LINQ pipeline. Single end-of-pipeline materialization is sufficient because SelectMany flattens all per-entity event lists during the ToArray evaluation — every list is enumerated to completion before any PublishAsync call runs. Cost: one small array allocation per scrape.

Tests

DomainEventScraperStateFilterTests.domain_event_scraper_materializes_events_before_publishing adapts the approach from @jf2s's closed PR #2586. Uses an ISendMyself domain event that mutates the DbContext during ApplyAsync to deterministically trigger the bug without needing live SQL Server / PostgreSQL. Verified the test fails on main and passes with this change.

All 10 tests in EfCoreTests/DomainEvents/ still pass.

Aggressive sweep — Wolverine.EntityFrameworkCore only

Per discussion in the issue thread, scope is Wolverine.EntityFrameworkCore. Audited every foreach in the package; no other risky lazy-enumeration patterns found:

• DbContextOutbox._scrapers — IDomainEventScraper[], materialized in constructor.
• EfCoreEnvelopeTransaction._scrapers — same, materialized.
• TenantedDbContextBuilder* — iterates _store.Source.AllActiveByTenant(), which returns IReadOnlyList<>. The BuildAllAsync body adds DbContexts to a local List<T> only — does not mutate the source.
• Codegen/* — runs at code-generation time, not on hot paths; no publishing side effects.

This was the only site that exhibited the publish-while-iterating-the-source pattern.

Credit

Same approach as the closed PR #2586 by @jf2s — credited in the test docstring and this PR.

Test plan

• New regression test fails on main
• New regression test passes with the fix
• All other DomainEvents tests pass (10/10)
• Audit of all foreach in Wolverine.EntityFrameworkCore — no other lazy-enumeration risks

🤖 Generated with Claude Code