初版功能完成

internal/appdir/appdir.go

@@ -0,0 +1,33 @@
+// Package appdir resolves files that belong to a portable RemLink package.
+package appdir
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// Executable returns the absolute directory containing the running executable.
+// Engineer and Site use this directory as their portable data root so launching
+// them from another working directory does not redirect generated files.
+func Executable() (string, error) {
+	executable, err := os.Executable()
+	if err != nil {
+		return "", fmt.Errorf("locate executable: %w", err)
+	}
+	executable, err = filepath.Abs(executable)
+	if err != nil {
+		return "", fmt.Errorf("resolve executable path: %w", err)
+	}
+	return filepath.Dir(executable), nil
+}
+
+// Join returns a path rooted at the directory containing the executable.
+func Join(elements ...string) (string, error) {
+	root, err := Executable()
+	if err != nil {
+		return "", err
+	}
+	parts := append([]string{root}, elements...)
+	return filepath.Join(parts...), nil
+}