Constructs an adapter for options — in particular for its
dimension, which is how one registration serves both §21 dimensions
(Rapier ships a separate 2D and 3D wasm build and a separate adapter for
each).
Must not initialize it: PhysicsWorld.initialize awaits
adapter.initialize (§37), and a solver built here may never be used if
"auto" rejects its capabilities.
A cheap, side-effect-free answer to "could this environment run this
solver at all?" — the presence of WebAssembly, of a native binding, of
SharedArrayBuffer.
Not the capability check: "auto" reads §37's capabilities off the
adapter this registration builds, which is exact and needs no probe. This
one only exists so a solver that cannot possibly load is skipped before it
is constructed.
How a solver package opts into selection — everything the registry needs to decide whether a solver fits, and how to build it.