Fix Windows build flow (#2487)

* Fix Windows build flow

* build(makefile): make windows recipes shell-safe

- avoid backslash line-continuation in Windows build-launcher recipe

- replace cmd-specific if-not-exist with PowerShell check in web build-frontend

* Fix Windows build flow

* build(makefile): make windows recipes shell-safe

- avoid backslash line-continuation in Windows build-launcher recipe

- replace cmd-specific if-not-exist with PowerShell check in web build-frontend

* build(web): avoid shell-expanding powershell vars in windows recipe

- rewrite build-frontend Windows command without PowerShell local vars

- keep install-stamp hash check logic

scripts/copydir.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+func main() {
+	if len(os.Args) != 3 {
+		fmt.Fprintf(os.Stderr, "usage: go run scripts/copydir.go <src> <dst>\n")
+		os.Exit(2)
+	}
+
+	src := os.Args[1]
+	dst := os.Args[2]
+
+	if err := os.RemoveAll(dst); err != nil {
+		fmt.Fprintf(os.Stderr, "remove %s: %v\n", dst, err)
+		os.Exit(1)
+	}
+
+	if err := copyTree(src, dst); err != nil {
+		fmt.Fprintf(os.Stderr, "copy %s -> %s: %v\n", src, dst, err)
+		os.Exit(1)
+	}
+}
+
+func copyTree(src, dst string) error {
+	info, err := os.Stat(src)
+	if err != nil {
+		return err
+	}
+	if !info.IsDir() {
+		return fmt.Errorf("source is not a directory: %s", src)
+	}
+
+	return filepath.Walk(src, func(path string, entry os.FileInfo, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+
+		rel, err := filepath.Rel(src, path)
+		if err != nil {
+			return err
+		}
+
+		target := dst
+		if rel != "." {
+			target = filepath.Join(dst, rel)
+		}
+
+		if entry.IsDir() {
+			return os.MkdirAll(target, entry.Mode())
+		}
+
+		return copyFile(path, target, entry.Mode())
+	})
+}
+
+func copyFile(src, dst string, mode os.FileMode) error {
+	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
+		return err
+	}
+
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	if _, err := io.Copy(out, in); err != nil {
+		return err
+	}
+
+	return out.Close()
+}