55 lines
3.1 KiB
Markdown
55 lines
3.1 KiB
Markdown
# CBDC settlement adapter (design)
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ISO 20022 remains the **instruction layer**; token/CBDC rails provide the **settlement layer**. as4-411 does not perform settlement; it may expose routing and settlement-rail metadata so that a **settlement adapter** (outside the core directory) can choose and invoke the correct settlement channel.
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---
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## Model
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- **Instruction layer:** ISO 20022 messages (e.g. pacs.008, pacs.009) over AS4; unchanged.
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- **Settlement layer:** One of RTGS | CBDC ledger | tokenized deposit. The directory can store a **settlement rail** capability per participant or endpoint (or per routing artifact).
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- **Settlement adapter:** A component (gateway-side or separate service) that receives the resolved directive plus an instruction reference, and performs or triggers settlement on the appropriate rail. It is **outside** as4-411 core.
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---
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## Directory extensions
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- **Optional capability or metadata:** e.g. `settlement_rail` = `RTGS` | `CBDC` | `tokenized_deposit`.
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- **Optional wallet/DLT endpoint:** For CBDC, the directory may store a wallet or DLT endpoint (or reference) per participant; as4-411 resolves PartyId → AS4 endpoint (unchanged) and may optionally return `settlement_rail` and `wallet_endpoint` (or equivalent) in the directive or in extended metadata for the settlement adapter to use.
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- **RouteDirective extension:** See [route-directive.md](route-directive.md). Optional fields: `settlement_rail`, `wallet_endpoint` (or `settlement_endpoint`). Not required for MVP; add when CBDC/tokenized flows are in scope.
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---
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## Dual-track processing
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```mermaid
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flowchart LR
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ISO["ISO 20022 instruction"]
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AS4["AS4 transport"]
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Dir["as4-411 directory"]
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Adapter["Settlement adapter"]
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RTGS["RTGS"]
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CBDC["CBDC ledger"]
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ISO --> AS4
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Dir -->|"endpoint + settlement_rail"| Adapter
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AS4 --> Adapter
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Adapter --> RTGS
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Adapter --> CBDC
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```
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1. Sender resolves PartyId via as4-411 → gets AS4 endpoint and optionally settlement_rail (and wallet/DLT endpoint if stored).
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2. Sender sends ISO 20022 over AS4 to receiver.
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3. Receiver (or a settlement adapter) uses the instruction plus optional settlement_rail / wallet_endpoint from directory to choose: settle via RTGS or via CBDC/tokenized ledger.
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---
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## Settlement adapter contract (minimal)
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A **settlement adapter** is a component that:
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- **Input:** Resolved RouteDirective (or equivalent), instruction reference (e.g. message id, business id), and optionally payload or reference to the ISO 20022 instruction.
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- **Output:** Settlement result or callback (e.g. accepted, rejected, pending). Format is out of scope of as4-411; defined by the gateway or scheme.
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- **Responsibility:** Map directive + instruction to the correct rail (RTGS, CBDC, tokenized deposit) and invoke the appropriate settlement API or ledger.
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as4-411 does **not** implement this interface; it only provides routing directives and, when extended, optional settlement_rail and wallet_endpoint so that an external adapter can be implemented. No full implementation of a CBDC settlement adapter is required in this add-on; a stub or placeholder may be added in packages/connectors or packages/core for tests if desired.
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