fix: improve endgame clock and gameplay stability

internal/common/game_clock_test.go

@@ -42,6 +42,36 @@ func TestGameClockSharedStateAndReset(t *testing.T) {
 	if string(before) != string(after) {
 		t.Fatal("read rewrote state")
 	}
+	begin := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
+	end := begin.Add(24 * time.Hour)
+	if _, err := SetGameTimeWindow(begin, end); err != nil {
+		t.Fatal(err)
+	}
+	window, err := ReadGameClock()
+	if err != nil || window.WindowBeginMS != begin.UnixMilli() || window.WindowEndMS != end.UnixMilli() {
+		t.Fatalf("window not saved: %+v %v", window, err)
+	}
+	// Simulate the clock having advanced beyond the end without waiting a day.
+	window.OffsetMS = end.Add(time.Hour).UnixMilli() - time.Now().UnixMilli()
+	raw, _ = json.Marshal(window)
+	if err := os.WriteFile(cfg.GameClock.StateFile, raw, 0600); err != nil {
+		t.Fatal(err)
+	}
+	now, err = GameTime()
+	if err != nil || now.Sub(begin.Add(time.Hour)) < 0 || now.Sub(begin.Add(time.Hour)) > time.Second {
+		t.Fatalf("window did not wrap: %v %v", now, err)
+	}
+	before, _ = os.ReadFile(cfg.GameClock.StateFile)
+	if _, err := GameTime(); err != nil {
+		t.Fatal(err)
+	}
+	after, _ = os.ReadFile(cfg.GameClock.StateFile)
+	if string(before) != string(after) {
+		t.Fatal("window read rewrote state")
+	}
+	if _, err := SetGameTimeWindow(end, begin); err == nil {
+		t.Fatal("invalid window accepted")
+	}
 	if _, err := SetGameTime(nil); err != nil {
 		t.Fatal(err)
 	}
@@ -49,6 +79,10 @@ func TestGameClockSharedStateAndReset(t *testing.T) {
 	if err != nil || time.Since(now).Abs() > time.Second {
 		t.Fatalf("real time not restored: %v %v", now, err)
 	}
+	window, err = ReadGameClock()
+	if err != nil || window.WindowBeginMS != 0 || window.WindowEndMS != 0 {
+		t.Fatalf("reset retained window: %+v %v", window, err)
+	}
 	if err := os.WriteFile(cfg.GameClock.StateFile, []byte(`{"offset_ms":9223372036854775807}`), 0600); err != nil {
 		t.Fatal(err)
 	}