feat(bell): add alert acknowledgement vertical slice

Bell/internal/alert/alert_test.go

@@ -0,0 +1,43 @@
+package alert
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadRulesRejectsUnknownAndDuplicateValues(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "rules.json")
+	valid := `{"version":1,"rules":[{"tenant_id":1,"site_id":2,"rule_key":"zone-entry","display_name":"区域闯入","event_kind":"zone_entry","minimum_severity":"medium","enabled":true,"effective_from":"2026-08-11T00:00:00Z"}]}`
+	if err := os.WriteFile(path, []byte(valid), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	rules, err := LoadRules(path)
+	if err != nil || len(rules) != 1 {
+		t.Fatalf("load valid rules: %v %#v", err, rules)
+	}
+	if err := os.WriteFile(path, []byte(`{"version":1,"unknown":true,"rules":[]}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := LoadRules(path); err == nil {
+		t.Fatal("unknown rule document property was accepted")
+	}
+	if err := os.WriteFile(path, []byte(valid+` trailing`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := LoadRules(path); err == nil {
+		t.Fatal("trailing rule file data was accepted")
+	}
+}
+
+func TestSeverityRankIsStable(t *testing.T) {
+	for index, value := range []string{"low", "medium", "high", "critical"} {
+		rank, ok := SeverityRank(value)
+		if !ok || rank != index {
+			t.Fatalf("rank %q: %d %v", value, rank, ok)
+		}
+	}
+	if _, ok := SeverityRank("urgent"); ok {
+		t.Fatal("unknown severity was accepted")
+	}
+}