fix(schema): require durable decision binding

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a02e47-6aac-7ee1-914d-0584c75d3c81

schemas/action_authorization.schema.json

@@ -19,7 +19,12 @@
     "request": {"$ref": "https://flex-auth.netkingdom/schemas/check_request.schema.json"},
     "validity": {"$ref": "#/$defs/validity"},
     "approvals": {"$ref": "#/$defs/approvals"},
-    "decision": {"$ref": "https://flex-auth.netkingdom/schemas/decision_envelope.schema.json"},
+    "decision": {
+      "allOf": [
+        {"$ref": "https://flex-auth.netkingdom/schemas/decision_envelope.schema.json"},
+        {"required": ["binding"]}
+      ]
+    },
     "provenance": {"type": "object", "additionalProperties": true}
   },
   "allOf": [