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docs/API.md is the authoritative interface reference: exports, Arbiter methods, check options/result shape with contract invariants, all ten relation configuration formats, valueManager, partial graphs (raw spec + pre-built context, precedence contract), snapshots (format, frozen restore, trust boundary), reachability (null-defer contract), OWAFusion, audit hook, errors, reason codes, and the validity taxonomy. README gains a capabilities section (what the engine does and does not do) and links the reference, per the map-vs-manual split. The reference pass surfaced one interface gap: PartialGraphContext — a first-class public type used in the pre-built overlay form — was not exported. It is now part of the public surface. Verified claims against source (overlay spec keys: challenges/ challengeProofs not proofs; qualitative routing via qualitative: true / scaleName; simpleBinary shape; reason enum; config formats). Rigor 251/251, full suite 853/791/0.