Add const parameter to Object

utoipa/src/openapi/schema.rs

@@ -1067,6 +1067,19 @@ builder! {
         /// See more details at <https://json-schema.org/understanding-json-schema/reference/non_json_data#contentmediatype>
         #[serde(skip_serializing_if = "String::is_empty", default)]
         pub content_media_type: String,
+
+        /// Specifies a single permissible value for this schema.
+        ///
+        /// When present, the schema validates only if the instance equals this exact value.
+        /// This is typically used for discriminator properties in polymorphic schemas or
+        /// for fixed protocol fields.
+        ///
+        /// Equivalent to a single-element `enum` but semantically indicates an immutable,
+        /// predetermined value rather than a choice among alternatives.
+        ///
+        /// See more details at <https://spec.openapis.org/oas/v3.2.0.html#annotated-enumerations>
+        #[serde(rename = "const")]
+        pub const_: Option<String>,
     }
 }