Extract the compliance library as source-only NuGet JasperFx.Events.ComplianceTests (P3.3)

[jeremydmiller]

Part of #5110. Blocked by P3.1a/b/c proving the seam in Marten (and ideally P3.2a so the shared sources can use the generic registry forms). Target repo: JasperFx/jasperfx for the package; a Marten PR switches consumption.

Move Marten.Testing/Compliance/ (seam types + abstract suites + shared aggregate/event fixture types) to the jasperfx repo, packaged as a source-only NuGet: contentFiles C# sources, no compiled assembly.

Why source-only is forced, not preferred:

• JasperFx.Events.SourceGenerator emits aggregate dispatchers per consuming assembly and binds each product's own session type (param matching by type-name suffix) — aggregates in a compiled DLL cannot dispatch correctly for both stores.
• Compiling in the consumer also sidesteps JasperFx/Weasel version skew between the repos and the LangVersion/ImplicitUsings differences (sources are authored to the C#13 / explicit-usings floor).

Package requirements:

• Declares compile-time expectations (JasperFx.Events, xunit.v3.extensibility.core) as documentation/dependency floor, not binary refs
• No Main, no xunit.runner.json, no runner packages — runner/parallelization config stays repo-owned
• Greenfield in jasperfx: every existing test project there is IsPackable=false; this becomes the repo's first packable test asset
• Versioned like the other JasperFx packages so consumers pin and roll forward deliberately

Marten side: EventSourcingTests drops the local Compile-links and references the package; the concrete Marten fixture and subclasses stay in the Marten repo. Verify the full ES suite is unchanged before/after the switch.

🤖 Generated with Claude Code

[jeremydmiller]

Done — JasperFx.Events.ComplianceTests 2.37.1 is published to NuGet (jasperfx#607, merged; the whole JasperFx 2.37.x line shipped together).

Marten consumption switches in #5122; Polecat adopts in polecat#393.

Packaging shape as shipped, all of it verified end to end against both stores before publish:

• contentFiles/cs/any/JasperFx.Events.ComplianceTests/** with buildAction="Compile", IncludeBuildOutput=false — no lib/, no compiled assembly.
• Dependencies: JasperFx.Events, xunit.v3.extensibility.core, xunit.v3.assert, Shouldly. Note the second one — a shared test library must never reference xunit.v3 itself, which forces OutputType=Exe onto every consumer.
• Authored to the shared floor: LangVersion 13, ImplicitUsings off, zero InternalsVisibleTo required.
• Local/ in the source tree carries a placeholder session alias so the jasperfx repo type-checks the sources without a concrete store; it is excluded from the package.

Two things worth recording that only came out of doing it:

1. Assert.Skip is not in xunit.v3.extensibility.core. Capability gating needs xunit.v3.assert as well. The declarative alternative ([Fact(SkipUnless = ...)]) is not usable here — xunit v3 requires a static property for it, which cannot consult a per-store fixture instance.
2. Each consumer supplies a one-line global alias naming its read session (global using ComplianceQuerySession = Marten.IQuerySession;). The shared self-aggregating fixtures declare EvolveAsync(IEvent, ComplianceQuerySession), and the source generator resolves the parameter by type name, so the alias is enough to bind one shared source file to both products. This is documented in the package README.

[jeremydmiller]

Landed in #5122, merged to master as 4cfe6c5a2. (GitHub only auto-closed #5111 — the PR body listed the four in one Closes clause and only the first is parsed.)