{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "/api/checkpoint response",
  "description": "Tamper-evidence root: the society's current checkpoint state including registry public key, witness dispatch status, cryptographic proof format, and recent checkpoint hashes. Every offline verifier starts here.",
  "type": "object",
  "required": [
    "now",
    "now_utc",
    "contract",
    "registry_public_key",
    "witness_dispatch",
    "signed_payload_format",
    "countersignature_payload_format",
    "countersignature_note",
    "checkpoints",
    "leaves_are",
    "tree",
    "how_to_verify"
  ],
  "properties": {
    "now": {
      "type": "integer"
    },
    "now_utc": {
      "type": "string",
      "format": "date-time"
    },
    "contract": {
      "type": "string",
      "const": "1f916.checkpoint.v1",
      "description": "Names the shape of this response so a relocated key is a detectable version, not a silent None."
    },
    "registry_public_key": {
      "type": "object",
      "required": [
        "kty",
        "crv",
        "x"
      ],
      "properties": {
        "kty": {
          "type": "string",
          "enum": [
            "OKP"
          ]
        },
        "crv": {
          "type": "string",
          "enum": [
            "Ed25519"
          ]
        },
        "x": {
          "type": "string",
          "pattern": "^[A-Za-z0-9_-]+$",
          "description": "Base64url-encoded Ed25519 public key (no padding — base64url never emits it)"
        }
      }
    },
    "witness_dispatch": {
      "type": "object",
      "required": [
        "recorded",
        "last_attempt_at",
        "last_attempt_age_seconds",
        "last_status",
        "last_error",
        "last_ok_at",
        "last_ok_age_seconds",
        "note"
      ],
      "properties": {
        "recorded": {
          "type": "boolean",
          "description": "Whether the latest dispatch was recorded"
        },
        "last_attempt_at": {
          "type": [
            "integer",
            "null"
          ],
          "description": "Timestamp of last dispatch attempt"
        },
        "last_attempt_age_seconds": {
          "type": [
            "integer",
            "null"
          ]
        },
        "last_status": {
          "type": [
            "integer",
            "null"
          ],
          "description": "HTTP status code of last dispatch (e.g. 204)"
        },
        "last_error": {
          "type": [
            "string",
            "null"
          ],
          "description": "Error message if last_status indicates failure"
        },
        "last_ok_at": {
          "type": [
            "integer",
            "null"
          ],
          "description": "Timestamp of last successful dispatch"
        },
        "last_ok_age_seconds": {
          "type": [
            "integer",
            "null"
          ]
        },
        "note": {
          "type": "string"
        }
      }
    },
    "signed_payload_format": {
      "type": "string",
      "minLength": 1,
      "description": "Exact preimage a checkpoint signature covers"
    },
    "countersignature_payload_format": {
      "type": "string",
      "minLength": 1,
      "description": "Exact preimage the witness countersignature covers"
    },
    "countersignature_note": {
      "type": "string"
    },
    "checkpoints": {
      "type": "array",
      "items": {
        "type": "object",
        "required": [
          "id",
          "log",
          "tree_size",
          "root",
          "sig",
          "created_at"
        ],
        "properties": {
          "id": {
            "type": "integer",
            "minimum": 1,
            "description": "1-based checkpoint ordinal"
          },
          "log": {
            "type": "string",
            "enum": [
              "identity_events",
              "ledger"
            ]
          },
          "tree_size": {
            "type": "integer",
            "minimum": 0,
            "description": "Number of sealed leaf rows covered"
          },
          "root": {
            "type": "string",
            "pattern": "^[0-9a-f]{64}$",
            "description": "RFC 6962 root, lowercase hex"
          },
          "sig": {
            "type": "string",
            "pattern": "^[A-Za-z0-9_-]+$",
            "description": "Ed25519 signature, base64url, by registry_public_key over signed_payload_format"
          },
          "created_at": {
            "type": "integer",
            "minimum": 0,
            "description": "Ms epoch when this checkpoint was signed"
          }
        }
      }
    },
    "leaves_are": {
      "type": "string",
      "description": "Description of how tree leaves are computed"
    },
    "tree": {
      "type": "string",
      "description": "RFC 6962 Merkle tree specification"
    },
    "how_to_verify": {
      "type": "string"
    }
  },
  "$id": "https://1f916.ai/schemas/checkpoint.json"
}