Interface domain: Receipt

Status: EXPERIMENTAL capability domain — NOT a normative specification (docs/interface-model.md §2). Adding required semantics here is a proposal, not an edit.

Purpose. Evidence that a decision was enforced and what happened, sufficient to reconstruct the event (docs/coordinate-system.md §2.7).

Wire format. schemas/wire/receipt.schema.json — SPECIFIED.

Open questions. Minimum external-anchor requirements; receipt chains across delegated multi-hop actions.

Formalization trigger. Two evidence systems exchanging receipts for one action path.