fix(router): drop empty rules parsed from empty TOML arrays

aconfig parses an empty TOML array (rules = []) as a slice holding one
empty string, which the router then treated as a real rule. Empty rules
can never match a real domain; Add and Replace now drop them.

router/ruleset.go

@@ -28,7 +28,9 @@ func NewRuleSet(rules ...string) *RuleSet {
 }
 
 // Add appends rules that are not already present, using the raw rule string
-// as the membership key. Duplicates are ignored.
+// as the membership key. Duplicates are ignored. Empty rules are dropped:
+// aconfig parses an empty TOML array as [""], which would otherwise surface
+// as a rule that can never match a real domain.
 func (rs *RuleSet) Add(rules ...string) {
 	if len(rules) == 0 {
 		return
@@ -37,6 +39,9 @@ func (rs *RuleSet) Add(rules ...string) {
 	rs.mu.Lock()
 	defer rs.mu.Unlock()
 	for _, rule := range rules {
+		if rule == "" {
+			continue
+		}
 		if _, ok := rs.set[rule]; ok {
 			continue
 		}
@@ -59,6 +64,9 @@ func (rs *RuleSet) Replace(rules ...string) {
 	nextSet := make(map[string]struct{}, len(rules))
 	nextTree := suffixtree.NewNodeFromRules()
 	for _, rule := range rules {
+		if rule == "" {
+			continue
+		}
 		if _, ok := nextSet[rule]; ok {
 			continue
 		}

router/ruleset_test.go

@@ -210,3 +210,23 @@ func TestListFilteredPaginationAndSearch(t *testing.T) {
 		t.Fatalf("expected empty page with total 5, got %v (total %d)", rules, total)
 	}
 }
+
+func TestRuleSetDropsEmptyRules(t *testing.T) {
+	rs := NewRuleSet("a.com", "", "b.com")
+	list := rs.List()
+	if len(list) != 2 || list[0] != "a.com" || list[1] != "b.com" {
+		t.Fatalf("Add should drop empty rules: %q", list)
+	}
+
+	rs.Add("", "c.com")
+	list = rs.List()
+	if len(list) != 3 || list[2] != "c.com" {
+		t.Fatalf("Add should drop empty rules: %q", list)
+	}
+
+	rs.Replace("", "d.com")
+	list = rs.List()
+	if len(list) != 1 || list[0] != "d.com" {
+		t.Fatalf("Replace should drop empty rules: %q", list)
+	}
+}