chore: Add precommit checks for JSON schema.

.pre-commit-config.yaml

@@ -25,6 +25,24 @@ repos:
       - id: check-added-large-files
       - id: check-shebang-scripts-are-executable
       - id: check-executables-have-shebangs
+  # JSON Schema: validate UCP schema files against their declared meta-schema
+  - repo: https://github.com/python-jsonschema/check-jsonschema
+    rev: 0.33.0
+    hooks:
+      - id: check-metaschema
+        files: ^source/(schemas|discovery)/.*\.json$
+      - id: check-jsonschema
+        name: Validate OpenAPI definitions
+        files: ^source/(services/.*\.openapi\.json|handlers/.*/openapi\.json)$
+        args:
+          - --schemafile
+          - https://spec.openapis.org/oas/3.1/schema/2022-10-07
+      - id: check-jsonschema
+        name: Validate OpenRPC definitions
+        files: ^source/services/.*\.openrpc\.json$
+        args:
+          - --schemafile
+          - https://meta.open-rpc.org/
   # Python: Ruff
   - repo: https://github.com/astral-sh/ruff-pre-commit
     rev: v0.14.13

source/services/shopping/embedded.openrpc.json

@@ -2,6 +2,7 @@
   "openrpc": "1.3.2",
   "info": {
     "title": "UCP Shopping Embedded Protocol",
+    "version": "draft",
     "description": "Embedded Protocol (EP) methods for the UCP shopping service. Methods are sent from Merchant to Host via postMessage using JSON-RPC 2.0. Method prefixes indicate capability scope: ep.{capability} (i.e. ep.checkout). Schema references are logical pointers - actual payload shape is determined by negotiated capabilities.\n\nEmbedded Protocol is a client-to-client postMessage interface, so there is no endpoint URL to access this API. Platforms detect merchant support for this protocol based on the presence of `services[\"dev.ucp.shopping\"][transport=embedded]` in discovery responses."
   },
   "servers": [],

source/services/shopping/mcp.openrpc.json

@@ -2,6 +2,7 @@
   "openrpc": "1.3.2",
   "info": {
     "title": "UCP Shopping Service",
+    "version": "draft",
     "description": "Canonical MCP/JSON-RPC interface for UCP Shopping service. Schema references are logical pointers - actual payload shape is determined by negotiated capabilities.\n\n**Endpoint Resolution:** This spec defines methods only. The endpoint URL MUST be obtained from the merchant's discovery profile at `/.well-known/ucp` under `services[\"dev.ucp.shopping\"][transport=mcp].endpoint`. The server entry below is a placeholder for tooling compatibility."
   },
   "servers": [

source/services/shopping/rest.openapi.json

@@ -2,6 +2,7 @@
   "openapi": "3.1.0",
   "info": {
     "title": "UCP Shopping Service",
+    "version": "draft",
     "description": "Canonical REST interface for UCP Shopping service. Schema references are logical pointers - actual payload shape is determined by negotiated capabilities.\n\n**Endpoint Resolution:** This spec defines operations only. The base URL MUST be obtained from the merchant's discovery profile at `/.well-known/ucp` under `services[\"dev.ucp.shopping\"][transport=rest].endpoint`. The `{endpoint}` server variable below is a placeholder for tooling compatibility."
   },
   "servers": [