These headers use fixed-width integer types without including <cstdint>.
glibc supplies it through other standard headers; musl does not.

--- a/hdr/spintransport.hpp	2025-06-05 17:51:31.000000000 +0200
+++ b/hdr/spintransport.hpp	2026-09-25 09:54:37.816756117 +0200
@@ -14,6 +14,7 @@
 #define SPINTRANSPORT_H_
 
 // C++ standard library headers
+#include <cstdint>
 #include <string>
 #include <vector>
 
--- a/hdr/vio.hpp	2025-06-05 17:51:31.000000000 +0200
+++ b/hdr/vio.hpp	2026-09-25 09:54:37.815706709 +0200
@@ -25,6 +25,7 @@
 #ifndef VIO_H_
 #define VIO_H_
 
+#include <cstdint>
 #include <fstream>
 #include <string>
 #include <iostream>
--- a/hdr/vmath.hpp	2025-06-05 17:51:31.000000000 +0200
+++ b/hdr/vmath.hpp	2026-09-25 09:54:37.811739113 +0200
@@ -10,6 +10,7 @@
 //------------------------------------------------------------------------------
 //
 
+#include <cstdint>
 #include <vector>
 #include <cmath>
 
--- a/hdr/vmpi.hpp	2025-06-05 17:51:31.000000000 +0200
+++ b/hdr/vmpi.hpp	2026-09-25 09:54:37.811988058 +0200
@@ -27,6 +27,7 @@
 //==========================================================
 // Includes
 //==========================================================
+#include <cstdint>
 #include "create.hpp"
 #include <cstdlib>
 #include <string>