fix(installer): move set_var before tokio runtime and fix build.rs cross-compile

- Move VP_HOME set_var and resolve_install_dir to main() before the
  tokio multi-thread runtime is created, ensuring no other threads
  can race on env var access (fixes UB safety concern).
- Use CARGO_CFG_TARGET_OS in build.rs instead of #[cfg(windows)] so
  the DLL security linker flag is correctly emitted when cross-compiling
  from a non-Windows host to a Windows target.

Author: fengmk2

crates/vite_installer/build.rs

@@ -2,6 +2,9 @@ fn main() {
     // On Windows, set DEPENDENTLOADFLAG to only search system32 for DLLs at load time.
     // This prevents DLL hijacking when the installer is downloaded to a folder
     // containing malicious DLLs (e.g. Downloads). Matches rustup's approach.
-    #[cfg(windows)]
-    println!("cargo:rustc-link-arg=/DEPENDENTLOADFLAG:0x800");
+    // Use CARGO_CFG_TARGET_OS (not #[cfg(windows)]) so the flag is emitted
+    // correctly when cross-compiling from a non-Windows host.
+    if std::env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("windows") {
+        println!("cargo:rustc-link-arg=/DEPENDENTLOADFLAG:0x800");
+    }
 }

crates/vite_installer/src/main.rs

@@ -97,32 +97,31 @@ fn main() {
 
     let opts = cli::parse();
 
+    // Resolve install dir and set VP_HOME before starting the tokio runtime,
+    // so the unsafe set_var runs while we're still single-threaded.
+    let install_dir = match resolve_install_dir(&opts) {
+        Ok(dir) => dir,
+        Err(e) => {
+            print_error(&format!("Failed to resolve install directory: {e}"));
+            std::process::exit(1);
+        }
+    };
+    // Safety: called in main() before any threads are spawned.
+    unsafe { std::env::set_var("VP_HOME", install_dir.as_path()) };
+
     let rt = tokio::runtime::Builder::new_multi_thread().enable_all().build().unwrap_or_else(|e| {
         print_error(&format!("Failed to create async runtime: {e}"));
         std::process::exit(1);
     });
 
-    let code = rt.block_on(run(opts));
+    let code = rt.block_on(run(opts, install_dir));
     std::process::exit(code);
 }
 
 #[allow(clippy::print_stdout, clippy::print_stderr)]
-async fn run(mut opts: cli::Options) -> i32 {
-    let install_dir = match resolve_install_dir(&opts) {
-        Ok(dir) => dir,
-        Err(e) => {
-            print_error(&format!("Failed to resolve install directory: {e}"));
-            return 1;
-        }
-    };
+async fn run(mut opts: cli::Options, install_dir: AbsolutePathBuf) -> i32 {
     let install_dir_display = install_dir.as_path().to_string_lossy().to_string();
 
-    // Propagate the resolved install directory to child `vp` processes
-    // (refresh_shims, create_env_files, install_production_deps) so they
-    // find the correct home, especially for --install-dir overrides.
-    // Safety: no other threads are reading env vars at this point.
-    unsafe { std::env::set_var("VP_HOME", install_dir.as_path()) };
-
     // Pre-compute Node.js manager default before showing the menu,
     // so the user sees the resolved value and can override it.
     if !opts.no_node_manager {