{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "mark-v0",
  "title": "mark-v0",
  "type": "object",
  "additionalProperties": false,
  "required": ["schema", "content_hash", "kind", "as_of"],
  "properties": {
    "schema": { "const": "mark-v0" },
    "content_hash": {
      "type": "string",
      "pattern": "^[a-f0-9]{64}$",
      "description": "SHA-256 of a lint-passing envelope stored off-site."
    },
    "kind": { "enum": ["human", "agent", "joint"] },
    "as_of": { "type": "string", "format": "date-time" }
  }
}