Define downstream integration profiles and capability handshake

[GeneralPawz]

What

Specify the supported integration profiles for Rust leaf-crate consumers, Rust facade consumers, and native C/C++ consumers. Define how a caller discovers API/ABI version, enabled capabilities and providers, tolerance expectations, thread-safety, representation guarantees, and typed refusal without depending on implementation crate names.

Why now

The workspace has strong internal contracts, but a downstream application still has to infer which crate closure and provider combination forms a supported product surface. The C ABI, packaging, examples, and compatibility tests need one normative contract before they can converge.

Definition of done

• An ADR names each supported v0.4 integration profile and its compatibility promise.
• A versioned capability descriptor covers representation, operation, provider, and feature availability.
• Unsupported operations return typed refusal; they never silently fall back from exact to mesh.
• Unit, tolerance, coordinate, ownership, concurrency, and determinism expectations are explicit.
• The public capability table is generated or checked against executable evidence.
• A mutation proves the compatibility/capability gate fails when a promised capability disappears.

Non-goals

This does not declare every geometry operation implemented or freeze the eventual 1.0 API.

Area

architecture

Effort

Medium