fix(clients): resolve 2026-06-18 array-write review findings

- Client.Dotnet-030: add advise-supervisory to IsKnownGatewayCommand (was dead/unreachable, exit 2)
- Client.Go-035/036/037: usage+README list advise-supervisory; add session-id guard test; fix write2 README wording
- Client.Python-037/038: drop regressed 'scaffold' from pyproject; add advise-supervisory CLI tests
- Client.Rust-039/040: document write_array_elements/advise-supervisory in design doc; pin outer MxValue data_type==0
- Client.Java-049/050/051: sync CLIENT_VERSION to 0.1.2; add advise-supervisory test; guard negative uint32 inputs (pending windev gradle verification)

Client READMEs also updated for Server-057 add-family normalization wording.
.NET/Go/Python/Rust verified green locally; Java pending windev.

clients/rust/tests/client_behavior.rs

@@ -1212,7 +1212,9 @@ fn sparse_int32_value(
         .collect();
 
     MxValue {
-        data_type: MxDataType::Integer as i32,
+        // outer data_type must be 0 (Unspecified); the element type lives only
+        // inside MxSparseArray.element_data_type, matching the
+        // `..ProtoMxValue::default()` used in Session::write_array_elements.
         variant_type: String::new(),
         kind: Some(Kind::SparseArrayValue(MxSparseArray {
             element_data_type: MxDataType::Integer as i32,
@@ -1227,6 +1229,11 @@ fn sparse_int32_value(
 fn write_array_elements_proto_shape_has_sparse_oneof_kind() {
     let proto = sparse_int32_value(5, [(0, 10), (3, 30)]);
 
+    assert_eq!(
+        proto.data_type, 0,
+        "outer MxValue.data_type must be 0 (Unspecified); element type lives in element_data_type"
+    );
+
     let Kind::SparseArrayValue(ref sparse) = proto.kind.as_ref().unwrap() else {
         panic!("expected SparseArrayValue kind, got {:?}", proto.kind);
     };
@@ -1253,6 +1260,10 @@ fn write_array_elements_proto_shape_has_sparse_oneof_kind() {
 #[test]
 fn write_array_elements_empty_elements_is_valid_all_defaults() {
     let proto = sparse_int32_value(8, []);
+    assert_eq!(
+        proto.data_type, 0,
+        "outer MxValue.data_type must be 0 (Unspecified) even with no elements"
+    );
     let Kind::SparseArrayValue(ref sparse) = proto.kind.as_ref().unwrap() else {
         panic!("expected SparseArrayValue kind");
     };
@@ -1269,6 +1280,10 @@ fn sparse_array_value_round_trips_through_client_mx_value_projection_as_unset()
     // (e.g. a future version bug), the projection should degrade to Unset
     // rather than panic, because the enum variant is not readable.
     let proto = sparse_int32_value(4, [(1, 99)]);
+    assert_eq!(
+        proto.data_type, 0,
+        "outer MxValue.data_type must be 0 (Unspecified)"
+    );
     let client_value = ClientMxValue::from_proto(proto);
     assert_eq!(
         client_value.projection(),