Volume III replaces Volume II and the reader addendum of 31 August 2026. The volume is written around the institutional policy engine: PCE and AIA as the engine, OMA and STN as the open rails it enforces on, one policy-commit hash threading all four.

1. Narrative. The engine and the rails are separated on every page. §1 shows the constraint as it appears on the desk: rules and execution drift apart, evidence is rebuilt after the fact. §4 is one decision path across three enforcement targets. The rails' economics sit in one section, §9, as the substrate's case, not OnTrade's revenue.
2. Commercial model. §8 carries the licence model: Verify · Enforce · Report tiers on assets-under-policy bands, metered verified decisions and rulepack content, embedded and certified implementations. Never basis points of executed turnover, no matching fee, settlement rails passed through at cost; execution savings are measured and reported, never priced.
3. The language. The OnTrade Policy Language (OPL) is published as an open standard with a free reference compiler and conformance suite. The attestation on a bundle, the policyCommit registry and the conformance certificate remain OnTrade's.
4. Market anchors and status. The USD 10–16T citation is retired for the August 2026 on-chain figures and the BCG × ADDX / Citi / McKinsey projection range. Production focus is Mode 2 (confidential settlement); Modes 1 and 3 remain architecture.