ADR 0001: Value representation

• Status: accepted
• Date: 2026-09-20

Context

Every Scheme value must be able to carry a taint tag (SPEC L2) and a credential handle must be a value that can never be coerced into its secret.

Decision

scheme.Value is one tagged struct: Kind, a payload, and a Taint field. Not an interface hierarchy. Handle is a first-class Kind from the start; it prints as #<cred:class:id> and no builtin converts it to a string. The Taint field is reserved in bootstrap and left unset until Phase 6.

Consequences

• Taint propagation (P6) is a field copy in one dispatch path, not a refactor.
• Values are copied by value; the struct is wider than a pointer. Irrelevant next to LLM latency.
• Adding a kind is a deliberate act with a doc entry (see ADR 7).