fix(model): accept URL elicitation requests without elicitationId

crates/rmcp/src/model.rs

@@ -3934,6 +3934,7 @@ enum ElicitRequestParamsWire {
         meta: Option<RequestMetaObject>,
         message: String,
         url: String,
+        #[serde(default)]
         elicitation_id: String,
     },
     #[serde(untagged, rename_all = "camelCase")]
@@ -4043,6 +4044,7 @@ pub enum ElicitRequestParams {
         /// The client should direct the user to this URL to complete the elicitation.
         url: String,
         /// The unique identifier for this elicitation request.
+        /// Protocol `2026-07-28` removed this field: it is empty when absent.
         elicitation_id: String,
     },
 }
@@ -6138,6 +6140,17 @@ mod tests {
         assert_eq!(json_url, expected_url_json);
     }
 
+    #[test]
+    fn test_url_elicitation_without_elicitation_id() {
+        let params: ElicitRequestParams = serde_json::from_value(json!({
+            "mode": "url",
+            "url": "https://mcp.example.com/ui/set_api_key",
+            "message": "Please provide your API key to continue."
+        }))
+        .expect("Deserialization failed");
+        assert_eq!(serde_json::to_value(&params).unwrap()["elicitationId"], "");
+    }
+
     #[test]
     fn notification_without_params_should_deserialize_as_bare_jsonrpc_message() {
         let payload = b"{\"method\":\"notifications/initialized\",\"jsonrpc\":\"2.0\"}";

crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json

@@ -828,7 +828,8 @@
               ]
             },
             "elicitationId": {
-              "type": "string"
+              "type": "string",
+              "default": ""
             },
             "message": {
               "type": "string"
@@ -844,8 +845,7 @@
           "required": [
             "mode",
             "message",
-            "url",
-            "elicitationId"
+            "url"
           ]
         },
         {