feat: add durable schedule management and multi-node crash recovery

internal/timezone/zone_test.go

@@ -0,0 +1,38 @@
+package timezone
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestFrozenSnapshot(t *testing.T) {
+	if got := fmt.Sprintf("%x", sha256.Sum256(data)); got != "b2d18a7c8fa8142097a48c99609fb3c92db5ee98bc740294e57eab8ae9f94779" {
+		t.Fatal("snapshot changed without a new version")
+	}
+	t.Setenv("ZONEINFO", t.TempDir())
+	for _, name := range []string{"UTC", "Asia/Shanghai", "America/New_York", "Australia/Lord_Howe", "Pacific/Apia"} {
+		zone, err := Load(name, Version)
+		if err != nil || zone == nil {
+			t.Fatalf("load %s: %v", name, err)
+		}
+		again, err := Load(name, Version)
+		if err != nil || again != zone {
+			t.Fatal("cache changed")
+		}
+	}
+	zone, _ := Load("Asia/Shanghai", Version)
+	_, offset := time.Date(2026, 1, 1, 0, 0, 0, 0, zone).Zone()
+	if offset != 8*3600 {
+		t.Fatal("wrong frozen zone")
+	}
+	for _, name := range []string{"", "Local", "../UTC", "/etc/localtime"} {
+		if _, err := Load(name, Version); err == nil {
+			t.Fatal("accepted external timezone")
+		}
+	}
+	if _, err := Load("UTC", "unavailable-version"); err == nil {
+		t.Fatal("silently upgraded frozen version")
+	}
+}