ReceiptOS: Recomputable Evidence and Counterfactual Verifier Conformance

ReceiptOS is a recomputable evidence substrate for autonomous-agent actions. It defines an Evidence Capsule whose canonicalized, anchor-stripped contents determine a receipt root; admissibility is a gate rather than a score, and anchoring remains a pluggable commitment layer. The v0.8 artifact retains the v0.6 capsule model, threat analysis, and cross-specification composition while adding a formal, executable account of counterfactual verifier behavior.Counterfactual Conformance v0 evaluates ten authenticated decision-boundary witnesses in an exact ten-member Deterministic Counterfactual Neighborhood: eight semantic-neighbor members, one boundary-rejection member, and one composite-relational member. Counterfactual Traversal Stability v1 evaluates the same neighborhood under twelve frozen schedules, yielding 120/120 stable scheduled evaluations, including 110 non-canonical comparisons, with first-position profile coverage of 10/10 members. A separate runner-invoked fresh-worker repeat of the authenticated canonical order matched 10/10 member records and is reported separately from the frozen 120-evaluation profile.In parallel, Recursive Singleton Fold provides a co-equal mechanically closed result for terminal-eligibility semantics. The paper also reports a bounded TEE experimental evidence class and a worked ReceiptOS × WYRIWE composition with byte-exact recomputation across three separately written implementations. The claims are intentionally bounded: ReceiptOS does not establish source truth, universal verifier correctness, legal admissibility, or downstream policy correctness.