fix(windows): ensure memset_explicit symbol is properly exported for MinGW

- Add __MINGW32__ detection in memset_s_shim.c for proper EXPORT macro
- Add WIN32 and __WIN32__ defines when compiling the shim in build.rs
- The memset_explicit symbol is required by libsodium-sys-stable but not
  available in MinGW runtime
- The shim is compiled as a static library and linked before libsodium

src-tauri/build.rs

@@ -6,14 +6,19 @@ fn main() {
     println!("cargo:rerun-if-changed=.git/refs/tags");
 
     // Compile memset_explicit shim for Windows MinGW
-    if std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default() == "windows"
-        && std::env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default() == "gnu"
-    {
+    // libsodium-sys-stable uses memset_explicit which isn't available in MinGW
+    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+    let target_env = std::env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default();
+    
+    if target_os == "windows" && target_env == "gnu" {
         cc::Build::new()
             .file("memset_s_shim.c")
+            .define("WIN32", None)
+            .define("__WIN32__", None)
             .compile("memset_shim");
         println!("cargo:rerun-if-changed=memset_s_shim.c");
-        // Explicitly link the shim library
+        // Link the shim library - must be before libsodium in link order
+        // The shim provides memset_explicit which libsodium expects
         println!("cargo:rustc-link-lib=static=memset_shim");
     }
 

src-tauri/memset_s_shim.c

@@ -2,16 +2,29 @@
  *
  * libsodium-sys-stable expects memset_explicit which isn't available
  * in the MinGW runtime. This provides a compatible implementation.
+ *
+ * This shim is compiled as part of the build process when targeting
+ * Windows with MinGW (x86_64-w64-mingw32).
  */
 
 #include <string.h>
+#include <stddef.h>
 
-#ifdef _WIN32
-#define EXPORT __declspec(dllexport)
+/* 
+ * Windows symbol export macros.
+ * __declspec(dllexport) ensures the symbol is visible in the compiled object.
+ */
+#if defined(_WIN32) || defined(__WIN32__) || defined(__MINGW32__)
+    #define EXPORT __declspec(dllexport)
 #else
-#define EXPORT
+    #define EXPORT __attribute__((visibility("default")))
 #endif
 
+/*
+ * memset_explicit implementation - a secure memory clearing function.
+ * Uses volatile to prevent compiler optimization from removing the memset.
+ * This matches the signature expected by libsodium.
+ */
 EXPORT void memset_explicit(void *dest, int val, size_t n) {
     volatile unsigned char *p = (volatile unsigned char *)dest;
     while (n--) {