ADR 0043: Public numeric type identity and target availability

Historical-evidence note: verification paths named below record the evidence used when this ADR was accepted; deleted aggregate checks are not active architecture or release owners. Current ownership is the four-surface ASL tree, with per-ID AVS coverage projected into spec/evidence/release-traceability-readiness.json.

Decision scope

This ADR is the canonical ADR 0043 binding and availability checkpoint. Bit-exact specialized formats, operation/type legality, and numeric result rules remain open.

Context

The first ADR 0087 checkpoint separated five encoded type namespaces and fixed their raw-carrier widths, but it deliberately did not bind those catalog names to the public PTO type system. Without a checked binding, a familiar spelling such as FP8, FPL8, or F64 could be mistaken for a published numeric type, and a backend-supported C++ carrier could silently become architecture.

PTO names 16 public element-type identities and defines an A2/A3 and A5 availability baseline. A target profile may narrow support but cannot redefine portable PTO semantics. Simulator behavior is not a target-profile or numeric-result definition.

Decision

The generated spec/evidence/public-numeric-type-baseline.json ledger is the fail-closed ADR 0043 binding and availability checkpoint.

1. The public identities are three base floating types, five A5-only specialized floating types, and eight signed or unsigned integer types.
2. All 16 public types bind to PTO catalog identities. The three base floating types bind to FP16, BF16, and FP32; the five A5-only specialized floating types bind to E4M3, E5M2, HiF8, E1M2X2, and E2M1X2; and the eight integer types bind to S8, U8, S16, U16, S32, U32, S64, and U64.
3. A2/A3 supports those 11 base identities. A5 supports all 16 published identities. These are type-support facts only; they do not make every operation/type tuple legal and do not select a numeric result.
4. Nine catalog types remain outside the public inventory: FP64, TF32, HF32, E3M2, E2M3, E8M0, HiF4X2, S4X2, and U4X2. Their PTO architectural identity is unchanged, and none gains a public alias by implication.
5. Public type names and widths do not define NaN payloads, signaling behavior, subnormal handling, rounding, flags, saturation, conversion overflow, accumulation, or any other result rule. Those decisions remain open.

Consequences

S5-T2-A5 closes public type discovery, all 16 accepted catalog bindings, and the published A2/A3-versus-A5 type availability baseline. It does not accept ADR 0087, populate a domain result rule, select a variation-point route, or change the M4 maturity floor.

The remaining ADR 0087 work is finite and explicit: complete every scalar and tile operation/type/profile legality tuple, publish independent numeric result and exception vectors, record downstream byte-and-effect parity for the immutable hardware profile, and accept architecture and formal-model review against the exact 0.57.1 type contract. These four legality, vector, parity, and review residuals remain open.

Evidence

• spec/evidence/public-numeric-type-baseline.json
• scripts/generate-public-numeric-type-baseline
• spec/evidence/numeric-profile-decision-inputs.json
• spec/evidence/numeric-format-namespace-contract.json
• spec/evidence/executable-model-comparison.json
• scripts/check-catalogs