Define TxnOutput API in go/common/runtime

go/common/runtime/runtime.go

@@ -47,3 +47,13 @@ type Tag struct {
 	// Value is the tag value.
 	Value []byte
 }
+
+// TxnOutput is an enum that has either Success or Error defined, depending on
+// the result of the transaction call.
+// It is meant for deserializing CBOR of the corresponding Rust enum.
+type TxnOutput struct {
+	// Success can be of any type.
+	Success interface{}
+	// Error is a string describing the error message.
+	Error *string
+}