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Documentation Index

Fetch the complete documentation index at: https://docs.cast.digitalfinancehq.com/llms.txt

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CAST’s guarantees do not depend on the application behaving well. Seven structural invariants are enforced at the schema level — through foreign keys, triggers, rules, and unique indexes — so they hold against a bug, a migration, or a direct database write. They are structural impossibilities, not policies the code is trusted to follow.
An invariant enforced in application code is a promise. An invariant enforced in the schema is a fact. These seven are facts: there is no code path, including a direct INSERT, that can violate them.

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The seven

1

A Posting requires a Bilateral Event

Every ledger entry carries a non-nullable foreign key to the bilateral event that authorized it. A posting with no co-authored event behind it cannot be inserted.
2

A Bilateral Event requires a confirmed Work Order state

The co-authored event cannot exist unless the Work Order has reached the confirmed state — authorization precedes the record, not the other way around.
3

Lineage hash chain integrity across all events

Every event’s lineage hash chains to the prior state. A break in the chain is detectable, so tampering cannot pass silently.
4

A single active Policy Version at any time

A partial unique index makes “more than one active policy” unrepresentable. Exactly one policy governs at any moment.
5

Settlement export requires an approved Control track

Value cannot be exported for settlement unless the Work Order’s control track has reached approved — the decision is a precondition to the disbursement.
6

Hard-coded triggers cannot be policy-suppressed

First payment to a new vendor and any bank-account change are hard-coded triggers. No policy change can suppress them — closing the path by which a configuration edit, rather than a confirmation, moves a high-risk payment through.
7

Events are append-only — no updates, no deletes

The event log only grows. A correction is a new event, never an edit. The system never updates or deletes an event.

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Why seven, and why at the schema level

These are the invariants of the full architecture. They span the whole lifecycle — from the authorization gate, through the control decision, to settlement export — and they hold system-wide properties like lineage integrity and single-policy governance. Placing them in the schema rather than the application is the entire point. Application code changes weekly; the schema changes rarely and survives every refactor. A verifier reading the database in 2031 — with no access to the application that ran in 2026 — can confirm all seven held, because the constraints are part of the data model itself.

See five of the seven enforced in a working build

The Layer 0 demo operates on the bilateral loop and enforces five of these seven today; settlement-stage invariants are exercised as that scope is built.