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Nullis is one modular Soroban contract, not four deploy units. Splitting the protocol into separate contracts would only add cross-contract calls and bug surface. Internally, four modules cooperate behind a single entrypoint.

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The five layers

1 · The circuit

A Noir circuit proves, in zero knowledge: possession of a credential secret, membership of its commitment in the approved root, correct nullifier derivation, and binding to the exact action.

2 · The issuer

Builds the approved-credential Merkle tree, issues membership witnesses, and rotates the root to revoke. (v0 reference issuer — no real KYC.)

3 · The contract

One Soroban contract that registers policies, verifies proofs on-chain, prevents replay, and executes the bound action atomically.

4 · The SDK & CLI

@nullis/sdk submits verify_and_execute in one call; @nullis/cli validates policy manifests and renders receipts.
And the fifth: the Privacy Receipt — the inspectable artifact emitted after every decision, success and rejection alike.

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System diagram

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The contract modules

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Canonical events

Every decision emits typed events, so the whole flow is inspectable from the ledger: PolicyPublished · RootRotated · ProofVerified · ActionExecuted · ActionRejected(reason) · ReplayBlocked · ReceiptEmitted

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The execution adapter

v0 uses an escrow model: the contract holds test tokens and releases contract balance → recipient on success. This is a reference execution adapter, not the final design — the production path is an authorized transfer (sender → recipient in the same transaction).
The escrow adapter is deliberately labeled and disclosed. See the honesty table for what is real vs. what is a reference implementation.

Next: the atomic primitive

Walk verify_and_execute step by step — the exact order of checks.