Name the received JSON type in non-object params errors

Keep -32602 and existing validation order; tell callers to send the object itself.
Cover host routing, stdout fast paths, SDK calls and generated dispatch.

Card: SAU-317

cli/tests/host/core.rs

@@ -500,14 +500,119 @@ async fn unimplemented_core_methods_return_method_not_found() {
 async fn params_must_be_objects() {
     let w = TestWorld::new();
     let h = w.start().await;
+    for (params, kind) in [
+        (json!("{\"text\":\"hello\"}"), "a string"),
+        (json!([]), "an array"),
+        (json!(42), "a number"),
+        (json!(null), "null"),
+        (json!(true), "a boolean"),
+    ] {
+        let expected = json!({
+            "code": -32602,
+            "message": format!("params must be a JSON object, got {kind}. Send the object itself, not a JSON-encoded string.")
+        });
+        for method in ["probe.echo", "core.ps"] {
+            assert_eq!(h.call(method, params.clone()).await.unwrap_err(), expected);
+        }
+        assert_eq!(
+            h.call("core.call", json!({"method":"probe.echo", "params":params}))
+                .await
+                .unwrap_err(),
+            expected
+        );
+    }
+    let object = json!({"text":"hello"});
+    assert_eq!(call(&h, "probe.echo", object.clone()).await, object);
     assert_eq!(
-        h.call("probe.echo", json!([])).await.unwrap_err()["code"],
-        -32602
+        call(
+            &h,
+            "core.call",
+            json!({"method":"probe.echo", "params":object})
+        )
+        .await,
+        object
+    );
+    assert_eq!(
+        call(&h, "core.call", json!({"method":"probe.echo"})).await,
+        json!({})
     );
 
     h.stop().await;
 }
 
+/// PROTOCOL 3.1: stdout fast paths reject non-objects without changing defaults.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn stdout_params_must_be_objects() {
+    let w = TestWorld::new();
+    let h = w.start().await;
+    let mut notifications = h.subscribe();
+    for method in ["core.notify", "core.unlock", "probe.echo"] {
+        for (params, kind) in [
+            (json!("{}"), "a string"),
+            (json!([]), "an array"),
+            (json!(1.5), "a number"),
+            (json!(null), "null"),
+            (json!(false), "a boolean"),
+        ] {
+            let response = call(
+                &h,
+                "probe.raw_call",
+                json!({
+                    "jsonrpc":"2.0", "id":1, "method":method, "params":params
+                }),
+            )
+            .await;
+            assert_eq!(response["id"], 1);
+            assert_eq!(
+                response["error"],
+                json!({
+                    "code": -32602,
+                    "message": format!("params must be a JSON object, got {kind}. Send the object itself, not a JSON-encoded string.")
+                })
+            );
+        }
+        let params = match method {
+            "core.notify" => json!({"name":"valid", "params":{"n":1}}),
+            "core.unlock" => json!({"path":"/state/not-held"}),
+            _ => json!({"n":1}),
+        };
+        let response = call(
+            &h,
+            "probe.raw_call",
+            json!({
+                "jsonrpc":"2.0", "id":1, "method":method, "params":params
+            }),
+        )
+        .await;
+        assert_eq!(
+            response["result"],
+            if method == "probe.echo" {
+                params
+            } else {
+                Value::Null
+            }
+        );
+        assert!(response.get("error").is_none());
+        let omitted = call(
+            &h,
+            "probe.raw_call",
+            json!({
+                "jsonrpc":"2.0", "id":1, "method":method
+            }),
+        )
+        .await;
+        match method {
+            "core.notify" => {
+                assert_eq!(omitted["error"]["message"], "name must be a string");
+                assert_eq!(notifications.try_recv().unwrap()["params"]["name"], "valid");
+            }
+            "core.unlock" => assert_eq!(omitted["error"]["message"], "path must be a string"),
+            _ => assert_eq!(omitted["result"], json!({})),
+        }
+    }
+    h.stop().await;
+}
+
 /// PROTOCOL 3.9: exit without answer reports status and last logs.
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn exit_without_answer_reports_status_and_last_logs() {

cli/tests/plugins/probe/src/main.rs

@@ -470,6 +470,10 @@ fn dispatch(request: &Value, lines: &mut Lines) -> Option<Value> {
         "network" => network(params),
         "read" => read_file(params),
         "write" => write_file(params),
+        "raw_call" => {
+            send(params.clone());
+            receive(lines)
+        }
         "call" => outgoing_call(params, lines),
         "lock" => lock(params, lines),
         _ => {