{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://adcontextprotocol.org/schemas/3.2.1/core/version-envelope.json",
  "title": "AdCP Version Envelope",
  "description": "Release-precision AdCP protocol version negotiation fields. Composed via `allOf` into every AdCP request and response schema so the version semantics live in exactly one place. Distinct from `core/protocol-envelope.json`, which wraps responses at the transport layer (context_id / task_id / status / payload). This envelope is part of the payload itself.",
  "type": "object",
  "properties": {
    "adcp_version": {
      "type": "string",
      "description": "Release-precision AdCP version (VERSION.RELEASE, e.g. \"3.0\", \"3.1\", \"3.1-beta\"). On a request: the buyer's release pin — the seller validates against its supported_versions and returns VERSION_UNSUPPORTED on cross-major mismatch, or downshifts to the highest supported release within the same major. On a response: the release the seller actually served — clients SHOULD validate the response against that release's schema, not against their pin. Patches are not negotiated; surface them as build_version on capabilities for operational visibility. When omitted, falls back to adcp_major_version (deprecated) or server default. Buyers SHOULD emit both adcp_version and adcp_major_version through 3.x to remain compatible with sellers that only read the legacy field. NORMALIZATION: SDKs that read full-semver values from bundle metadata (e.g. ComplianceIndex.published_version = \"3.1.0-beta.1\") MUST normalize to release-precision (\"3.1-beta.1\") before emitting on the wire — meta-field values are NOT valid wire values.",
      "pattern": "^(?:0|[1-9]\\d*)\\.(?:0|[1-9]\\d*)(?:-[a-zA-Z0-9](?:[a-zA-Z0-9.-]*[a-zA-Z0-9])?)?$",
      "examples": [
        "3.0",
        "3.1",
        "3.1-beta",
        "3.1-rc.1"
      ]
    },
    "adcp_major_version": {
      "type": "integer",
      "deprecated": true,
      "description": "DEPRECATED in favor of adcp_version (release-precision string). Servers MUST continue to honor this field through 3.x. Removed in 4.0. Original semantics: the AdCP major version the buyer's payloads conform to. Sellers validate against their supported major_versions and return VERSION_UNSUPPORTED if unsupported. When omitted, the seller assumes its highest supported version.",
      "minimum": 1,
      "maximum": 99
    }
  }
}