Organize backend into product executable and shared Go modules

backend/shared/logging/mask/mask.go

@@ -0,0 +1,29 @@
+package mask
+
+import "strings"
+
+func Email(email string) string {
+	parts := strings.Split(email, "@")
+	if len(parts) != 2 {
+		return email
+	}
+	local := parts[0]
+	if len(local) > 2 {
+		local = local[:1] + "***" + local[len(local)-1:]
+	} else {
+		local = local[:1] + "***"
+	}
+	return local + "@" + parts[1]
+}
+
+func Emails(emails []string) []string {
+	if emails == nil {
+		return nil
+	}
+
+	masked := make([]string, len(emails))
+	for i, email := range emails {
+		masked[i] = Email(email)
+	}
+	return masked
+}

backend/shared/logging/mask/mask_test.go

@@ -0,0 +1,21 @@
+package mask
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestEmailsMasksEachEmail(t *testing.T) {
+	got := Emails([]string{"alice@example.com", "bo@example.org", "invalid"})
+	want := []string{"a***e@example.com", "b***@example.org", "invalid"}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("Emails() = %#v, want %#v", got, want)
+	}
+}
+
+func TestEmailsPreservesNil(t *testing.T) {
+	if got := Emails(nil); got != nil {
+		t.Fatalf("Emails(nil) = %#v, want nil", got)
+	}
+}