> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cast.digitalfinancehq.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Lineage

> The proof is the asset — and it is a property, not an object.

<Info>**`lineage()`** — a function over the five objects, not a sixth primitive.</Info>

Lineage is the immutable hash chain that links a posting back through the events, decisions, and policy version that created it. Because the chain is append-only and each link references the prior one, verifying a payment's full history becomes fast and reliable.

<Note>
  Model lineage as a property of the chain — never as a sixth box beside Event, Policy Version, Work Order, Posting, and Case. It is what connects them.
</Note>

## Independent replay

The defining feature of lineage is that **any third party can verify it without contacting either counterparty** — using only the database rows, the committed canonicalizer source, and a standard cryptographic library.

```ts verify.ts — independent replay theme={"dark"}
// Any third party, no counterparty contact
const ok = await replay(eventId);

// Standard libs only — no proprietary verifier
// - SHA256(canonicalize(payload, v1))
// - ECDSA-P256 signature check
// - X.509 chain validation

return {
  valid: ok,
  proves: "both parties confirmed",
  at: "signed timestamp",
  unmodified_since: true,
};
```

## Why the proof is the asset

A signature must still verify years later, even after the schema has gained new fields. CAST signs **canonicalized hashes, not rows** — so a 2026 signature over a payment still verifies in 2031. The canonicalization rule for each version is committed to the repository with a version tag, so anyone can reproduce the exact bytes that were signed.

<Note>
  Every posting is traceable back through the events, decisions, and policy version that produced it. That traceability is what makes a transaction insurable, financeable, and survivable in audit. **The subscription fee is the cost of producing this verifiable record.**
</Note>

<Card title="The economics of verifiable proof" icon="scale-balanced" href="/foundations/liability-as-a-service">
  Why value accrues to whoever can underwrite the output.
</Card>