{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://real-life.org/trust-tasks/delivery-ack/0.1",
  "title": "Payload: delivery-ack/0.1 (rltp-delivery@0.17, target Trust Tasks framework 0.4)",
  "description": "Payload schema per Trust Tasks 6.3 ($id = Type URI, describes only the payload). Arrival acknowledgement per Delivery Contract 4.2: machine-generated at the durable recording of the referenced document's defined effect; the document carrying this payload MUST carry a proof under its issuer anchor; meaning is arrival only, never acceptance or any human act.",
  "type": "object",
  "required": [
    "ref",
    "meaning"
  ],
  "additionalProperties": false,
  "properties": {
    "ref": {
      "type": "string",
      "description": "multibase-encoded multihash (sha2-256: 0x12 0x20 + 32 bytes) over JCS-canonicalized input; emit 'u' (46 chars after header), accept 'u'/'z' per CID 1.0; decoded multihash verified at parse",
      "pattern": "^(u[A-Za-z0-9_-]{46}|z[1-9A-HJ-NP-Za-km-z]{44,48})$"
    },
    "meaning": {
      "const": "received"
    }
  }
}