feat(03-02): add allow-listed database-default order helper

- Reject identifiers and directions outside the caller allow-list
- Emit ordinary ORDER BY without COLLATE so ICU pl-PL applies

Co-authored-by: Cursor <cursoragent@cursor.com>

lagoon/order.go

@@ -0,0 +1,46 @@
+package lagoon
+
+import (
+	"fmt"
+	"strings"
+
+	"gorm.io/gorm"
+)
+
+// OrderBy appends a database-default ORDER BY for an allow-listed qualified
+// column. Identifiers and directions are never taken from untrusted input:
+// column must match allowed exactly, and dir must be asc or desc. No COLLATE
+// is emitted; Postgres ICU pl-PL is the database default (CheckLocale).
+func OrderBy(db *gorm.DB, column, dir string, allowed []string) (*gorm.DB, error) {
+	if db == nil {
+		return nil, fmt.Errorf("lagoon: gorm db is nil")
+	}
+	clause, err := orderClause(column, dir, allowed)
+	if err != nil {
+		return nil, err
+	}
+	return db.Order(clause), nil
+}
+
+func orderClause(column, dir string, allowed []string) (string, error) {
+	if !allowListed(column, allowed) {
+		return "", fmt.Errorf("lagoon: order column %q is not allow-listed", column)
+	}
+	switch strings.ToLower(strings.TrimSpace(dir)) {
+	case "asc":
+		return column + " ASC", nil
+	case "desc":
+		return column + " DESC", nil
+	default:
+		return "", fmt.Errorf("lagoon: order direction %q is not allow-listed", dir)
+	}
+}
+
+func allowListed(column string, allowed []string) bool {
+	for _, a := range allowed {
+		if a == column {
+			return true
+		}
+	}
+	return false
+}

lagoon/order_test.go

@@ -0,0 +1,39 @@
+package lagoon
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestOrderClauseAllowList(t *testing.T) {
+	allowed := []string{"golem15_fonoteka_genres.name", "items.title"}
+
+	got, err := orderClause("golem15_fonoteka_genres.name", "asc", allowed)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "golem15_fonoteka_genres.name ASC" {
+		t.Fatalf("got %q", got)
+	}
+	if strings.Contains(strings.ToLower(got), "collate") {
+		t.Fatalf("must not emit COLLATE: %q", got)
+	}
+
+	got, err = orderClause("items.title", "DESC", allowed)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "items.title DESC" {
+		t.Fatalf("got %q", got)
+	}
+
+	if _, err := orderClause("golem15_fonoteka_genres.name;drop table x", "asc", allowed); err == nil {
+		t.Fatal("want reject unknown column")
+	}
+	if _, err := orderClause("golem15_fonoteka_genres.name", "ascending", allowed); err == nil {
+		t.Fatal("want reject unknown direction")
+	}
+	if _, err := OrderBy(nil, "items.title", "asc", allowed); err == nil {
+		t.Fatal("want nil db error")
+	}
+}