Return ErrNotSupported when the remote does not advertise Write()

The Hvac and Setpoint write helpers issued a write command without
checking whether the remote server feature advertises the Write()
operation for the corresponding function. Guard each write helper so it
returns api.ErrNotSupported unless the remote advertises Write(),
matching the existing LoadControl/DeviceConfiguration behaviour.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: andig

features/client/hvac.go

@@ -99,6 +99,12 @@ func (h *Hvac) WriteHvacOverrunListData(
 		return nil, api.ErrMissingData
 	}
 
+	// the remote server has to advertise the write operation for this function
+	operation := h.featureRemote.Operations()[model.FunctionTypeHvacOverrunListData]
+	if operation == nil || !operation.Write() {
+		return nil, api.ErrNotSupported
+	}
+
 	cmd := model.CmdType{
 		HvacOverrunListData: &model.HvacOverrunListDataType{
 			HvacOverrunData: data,
@@ -117,6 +123,12 @@ func (h *Hvac) WriteHvacSystemFunctionListData(
 		return nil, api.ErrMissingData
 	}
 
+	// the remote server has to advertise the write operation for this function
+	operation := h.featureRemote.Operations()[model.FunctionTypeHvacSystemFunctionListData]
+	if operation == nil || !operation.Write() {
+		return nil, api.ErrNotSupported
+	}
+
 	cmd := model.CmdType{
 		HvacSystemFunctionListData: &model.HvacSystemFunctionListDataType{
 			HvacSystemFunctionData: data,

features/client/setpoint.go

@@ -67,6 +67,12 @@ func (s *Setpoint) WriteSetpointListData(
 		return nil, api.ErrMissingData
 	}
 
+	// the remote server has to advertise the write operation for this function
+	operation := s.featureRemote.Operations()[model.FunctionTypeSetpointListData]
+	if operation == nil || !operation.Write() {
+		return nil, api.ErrNotSupported
+	}
+
 	cmd := model.CmdType{
 		SetpointListData: &model.SetpointListDataType{
 			SetpointData: data,