Native AOT on .NET 11 RC2: every value set ToString traps (SIGTRAP) in the default IFormattable.ToString of IValueSetFactory<TSet, T> #291

Problem

A Native AOT consumer published with the .NET 11 RC2 SDK (11.0.100-rc.2.26504.105, ILCompiler 11.0.0-rc.2, osx-arm64) dies with SIGTRAP (exit 133, nothing on stderr) on the first ToString() of any value set — Int32Set<Code>, Float64Set, Float64Set<Ratio>.Parse(…) printed, a set read from JSON and printed. The macOS crash report puts the trap in the instantiating stub ILCompiler emits for the interface's default implementation:

Internal_CompilerGenerated__Module___<__InstantiatingStub_4__>CodoMetis_ValueRanges_CodoMetis_ValueRanges_Core_IValueSetFactory_2<System___Canon__aot2_Code>__System_IFormattable_ToString +52
aot2_Program___Main__ +544

IValueSetFactory<TSet, T> implements IFormattable.ToString once, as a default interface method calling SetFormat.Format<TSet, T>((IValueSet<T>)this, …), and every set type's ToString() goes through it. TSet is always a class, so the instantiation is shared (__Canon) and the stub has to fetch the generic dictionary; on RC2 the stub is a brk. The ranges' IRangeFactory<TRange, T> has the same shape and does not trap.

Measured: the same program on .NET 10 with the 10.0.0 package runs; a net11.0 program against the unchanged 10.0.0 package traps the same way, so this is the toolchain, not the retarget's build; the managed (JIT) build of the same program runs. A library-free copy of the shape (generic interface, DIM IFormattable.ToString, generic static formatter, IntSet<T> over a struct) does not trap, so the trigger is narrower than the pattern; the next-closer copy is being tried for the upstream report.

The consumer smoke test's NativeAOT leg (test/consumer-smoke-test.sh) stops at aot-float64set-wrapper-read with no output after it, which is how this was found.

Change

Every set type (the twelve core families, their wrapper arities, and the five NodaTime families) implements IFormattable.ToString itself and its ToString() calls SetFormat.Format directly, so the default on the interface is never the implementation a compiled consumer runs. Public surface unchanged (explicit interface implementations). The interface keeps its default for documentation and for any implementer that has none. Upstream report to follow once a library-free repro traps.

Found by the #103 retarget's smoke test run.