id: ADR-0012 title: Adopt D9: every constitutive computation is a KernelSpec with generated bindings status: superseded date: 2026-09-13 deciders: [paul-heyse] level: decision principles: [DM-19, DM-25, DM-44, DM-52] blueprint: [§D9, §18.5, §21.4] review: not-required: neither review raised a finding against D9 evidence: Proposed supersedes: [] superseded-by: ADR-0043 revisit: A kernel needs a binding form the six generated ones cannot express, or a third-party compiled kernel package is admitted (§22, ADR-0037) verification: tests/conformance kernel-adapter equivalence tests; rust / codegen-diff

ADR-0012: Adopt D9: every constitutive computation is a KernelSpec with generated bindings

Context

Blueprint D9 gives every code-implemented constitutive computation a KernelSpec with identity, signature in physical types, mathematical behaviour, derivative availability, execution forms, failure behaviour and backend bindings, from which scalar, batched Arrow, derivative, DataFusion UDF, NL external-function and Pyomo bindings are generated.

Scope

Binds the kernel contract and the generated binding set. Which kernels exist is §9 and the reference packages.

Drivers

Six hand-written bindings per kernel is five too many; a kernel whose derivative availability is undeclared forces the Hessian profile to limited memory silently.

Options

Hand-written adapters per backend — rejected: they drift, and the NL and Pyomo forms must agree bit for bit with the native one. A trait per backend — rejected: the spec is data (D1), so the adapters are generated from it.

Outcome

One KernelSpec per computation; all six binding forms are generated; derivative availability and failure behaviour are declared, not inferred.

Consequences

Adding a kernel is a spec plus a Rust body plus tests; the adapters come from the generator and are committed and diffed (ADR-0031).

Compensating controls

Kernel-adapter equivalence tests compare scalar, batched and generated-UDF evaluation on the same inputs; KernelSpec digests enter the plan fingerprint (ADR-0019).

Confirmation

rust / test runs the equivalence layer; rust / codegen-diff fails if a generated adapter is edited by hand.

Pros and cons

The spec is verbose; it is also the only place a kernel’s derivative and failure contract is written down.

More information

Blueprint §D9, §18.5 (generated kernel adapters), §21.4 (opaque kernels and ASL), §22.3.

Status history

• 2026-09-13 — accepted with the repository-seeding pull request (backfilled from blueprint revision 3).
• 2026-09-13 — superseded by ADR-0043.