fix(client): correctly set stream key for multipart

Author: stainless-app[bot]

appdeployment.go

@@ -317,6 +317,9 @@ func (r AppDeploymentNewParams) MarshalMultipart() (data []byte, contentType str
 	buf := bytes.NewBuffer(nil)
 	writer := multipart.NewWriter(buf)
 	err = apiform.MarshalRoot(r, writer)
+	if err == nil {
+		err = apiform.WriteExtras(writer, r.ExtraFields())
+	}
 	if err != nil {
 		writer.Close()
 		return nil, "", err

internal/apiform/encoder.go

@@ -449,3 +449,17 @@ func (e *encoder) newMapEncoder(_ reflect.Type) encoderFunc {
 		return e.encodeMapEntries(key, value, writer)
 	}
 }
+
+func WriteExtras(writer *multipart.Writer, extras map[string]any) (err error) {
+	for k, v := range extras {
+		str, ok := v.(string)
+		if !ok {
+			break
+		}
+		err = writer.WriteField(k, str)
+		if err != nil {
+			break
+		}
+	}
+	return
+}