test(mcp): from_mcp wraps non-object tool arguments as {"value": …} (COV-12 review-002)

Wire-level round trip through the real rmcp server: a scalar input
reaches the remote tool as {"value": <input>}, matching the
value_to_json_object wrap.

tests/from_mcp_integration.rs

@@ -420,6 +420,37 @@ async fn import_refuses_tool_name_containing_slash() {
     }
 }
 
+#[tokio::test]
+async fn forwarding_handler_wraps_non_object_input_as_value_field() {
+    // A scalar/array tool argument cannot be a JSON object on the MCP
+    // wire; the adapter wraps it as {"value": <input>} (review-002
+    // from_mcp :460-468 arm). Proven over the real rmcp round trip: the
+    // echo server reflects the arguments object back.
+    let (endpoint, _handle) = spawn_server().await;
+    let adapter = FromMCP::new(endpoint, "echo");
+    let bundles = adapter.import().await.expect("import succeeds");
+    let echo = bundles
+        .into_iter()
+        .find(|b| b.spec.name == "echo/echo")
+        .expect("echo tool present");
+
+    let ctx = test_context("req-wrap", Capabilities::new());
+    let response = match &echo.handler {
+        HandlerKind::Once(h) => h(serde_json::json!("bare-scalar"), ctx).await,
+        HandlerKind::Stream(_) | HandlerKind::Sink(_) => panic!("expected Once handler"),
+    };
+    match response.result {
+        Ok(Value::Object(obj)) => {
+            assert_eq!(
+                obj.get("echoed"),
+                Some(&serde_json::json!({ "value": "bare-scalar" })),
+                "non-object input must reach the wire as {{\"value\": …}}: got {obj:?}"
+            );
+        }
+        other => panic!("expected object structured content, got {other:?}"),
+    }
+}
+
 #[tokio::test]
 async fn forwarding_handler_maps_json_rpc_tool_error_with_code_fidelity() {
     // A server whose `call_tool` returns a JSON-RPC error (rmcp