JasperFx#276 Phase 2: Adopt FEC-free projection apply-method dispatch

[jeremydmiller]

Summary

Marten 9 picks up the JasperFx 2.0 alphas that retire FastExpressionCompiler-driven projection apply dispatch. Aggregation now flows exclusively through the source-generator-emitted [GeneratedEvolver] partial classes produced by JasperFx.Events.SourceGenerator — no runtime reflection over Apply / Create / ShouldDelete methods. This PR is the Marten-side migration to that path.

References JasperFx/jasperfx#276 (Phase 1, FEC retirement, already merged). Also picks up:

• AggregateEvolverGenerator emits ungrouped tuple for DetermineActionAsync delete branch jasperfx#290 — DetermineActionAsync delete-branch tuple-wrap
• AggregateEvolverGenerator does not handle projection classes nested inside parent types jasperfx#292 — nested-class projection support
• AggregateEvolverGenerator does not emit a dispatcher for Projections.Snapshot<T> self-aggregating registrations jasperfx#293 — Snapshot<T>() self-aggregating dispatch
• Source generator: DiscoverMethodsOnType doesn't walk inherited Apply/Create/ShouldDelete jasperfx#295 — SG analyzer walks the inheritance chain
• AggregateEvolverGenerator alpha.4: handler-argument binding, duplicate switch cases, and required-member init bugs jasperfx#297 — handler-argument binding, duplicate switch cases, required-member init
• [#276 follow-up] tryUseAssemblyRegisteredEvolver early-exits on HasShouldDeleteMethods before checking IGeneratedSyncDetermineAction jasperfx#298 — tryUseAssemblyRegisteredEvolver honors IGeneratedSyncDetermineAction
• Make UpsertStyle = Standard the new default #299 (codegen fixes), Support Select(x => x.Json()) select projections for fetching raw JSON #301 (dispatch-pattern support: event-shaped ctors, [Identity] attr, required-member init, ctor-side DeleteEvent<T>, async self-aggregating)

Pkg bumps

Pkg	Before	After
JasperFx	2.0.0-alpha.13	2.0.0-alpha.14
JasperFx.Events	2.0.0-alpha.12	2.0.0-alpha.13
JasperFx.Events.SourceGenerator	2.0.0-alpha.5	2.0.0-alpha.6
Marten	9.0.0-alpha.2	9.0.0-alpha.3

Migration done

• ~80 projection-subclass test types made partial so the SG can emit a sibling dispatcher.
• Two inline-lambda regression files deleted (the APIs they exercised — ProjectEvent<T>(...) / CreateEvent<T>(...) / DeleteEvent<T>(predicate) — are gone in the JasperFx 2.0 alphas).
• samples/EventSourcingIntro/Program.cs + Helpdesk Incidents/* samples migrated to method conventions; affected doc snippets (docs/events/projections/*.md) re-rendered via mdsnippets.
• Bug_3665_compiling_with_private_members deleted — exercised the now-dropped private-Apply pattern.
• Three aggregation_projection_validation_rules tests removed — asserted on specific old-runtime error messages the SG no longer produces (the SG silently skips signatures it can't dispatch; covered in the migration guide).
• Invoice in ScenarioAggregateAndRepository flipped to public Apply methods + public parameterless ctor.
• Test projects that declare their own projection / aggregate types now reference JasperFx.Events.SourceGenerator directly as an analyzer (Marten.csproj keeps PrivateAssets=\"all\" so the analyzer doesn't flow transitively): CoreTests.csproj, DocumentDbTests.csproj, MultiTenancyTests.csproj, ValueTypeTests.csproj. Mirrors the existing wiring on EventSourcingTests / DaemonTests.
• New migration-guide entries:
  • Aggregation method visibility now required to be public — handlers must be public; pre-9.0 reflection picked up private / internal / protected members. Includes the before/after rewrite for the documented Aggregate-as-Repository pattern and a callout that the SG falls back to RuntimeHelpers.GetUninitializedObject(typeof(T)) when the parameterless ctor isn't public (field initializers do not run in that fallback).
  • Identity-by-attribute on non-Id members — annotating with [Identity] is the supported way to override the Id-by-convention rule. The runtime Schema.For<T>().Identity(x => ...) override isn't visible to the SG at compile time and can't be honored.
  • Required-member aggregates — supported via new T { Required = default! }; Apply(event, s); in the null-snapshot branch.
  • Validation-rule behavior changes — covers the three retired runtime checks.

Documented limitations (skipped tests)

• stream_aggregation.stream_id_is_set_as_string — runtime identity override invisible to the SG.
• rebuilds_with_serialization_or_poison_pill_events.rebuild_the_projection_skip_failed_events — SG-emitted IGeneratedSyncDetermineAction batches events in one call, so per-event dead-letter routing under SkipApplyErrors=true no longer fires. Tracked as jasperfx#303.

Test plan

Full Marten test run against the published NuGets:

Project	Pass / Fail / Skip
EventSourcingTests	1,320 / 0 / 7
DaemonTests	183 / 0 / 1
CoreTests	444 / 0 / 1
DocumentDbTests	987 / 0 / 1
MultiTenancyTests	128 / 0 / 0
PatchingTests	122 / 0 / 1
LinqTests	1,257 / 0 / 1
CompiledQueryTests	9 / 0 / 0

Pre-existing failures not introduced by this PR (also fail on master):

• ValueTypeTests — 127 strong-typed-id failures, tracked in #4474, milestoned 9.0.

• Marten.CommandLine.Tests — compile errors (IProjectionStore / ProjectionLifecycle / AsyncProjectionShard missing) inherited from a JasperFx rename. Out of scope here.

• CI green across the matrix (.NET 9 / .NET 10 × Newtonsoft / System.Text.Json × Postgres 15 / latest).

• One-click smoke against the new alphas in a downstream consumer project — confirm Snapshot<T>() registrations and AggregateStreamAsync<T>() call sites get an SG-emitted dispatcher.

Commit shape

1. JasperFx#276 Phase 2: Adopt FEC-free source-generated projection dispatch — pkg bumps, ~80-file source migration, csproj analyzer wiring, deleted/skipped tests.
2. docs: 9.0 migration entries for the new dispatch-pattern requirements — docs/migration-guide.md only.
3. Bump Marten to 9.0.0-alpha.3 — Directory.Build.props.

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