Validate campaign save steps

src/game/state/campaignState.ts

@@ -388,6 +388,18 @@ const campaignBattleSteps: Record<string, { victory: CampaignStep; retry: Campai
   'sixty-sixth-battle-wuzhang-final': { victory: 'sixty-sixth-camp', retry: 'sixty-sixth-battle' }
 };
 
+const campaignStepIds = new Set<CampaignStep>([
+  'new',
+  'prologue',
+  'first-victory-story',
+  'ending-complete',
+  'hanzhong-king-camp',
+  'shu-han-foundation-camp',
+  'baidi-entrustment-camp',
+  'northern-campaign-prep-camp',
+  ...Object.values(campaignBattleSteps).flatMap(({ victory, retry }) => [victory, retry])
+]);
+
 export type CampaignSaveSlotSummary = {
   slot: number;
   exists: boolean;
@@ -787,6 +799,7 @@ function normalizeCampaignState(state: Partial<CampaignState>): CampaignState {
   };
   normalized.version = 1;
   normalized.updatedAt = typeof normalized.updatedAt === 'string' && normalized.updatedAt ? normalized.updatedAt : new Date().toISOString();
+  normalized.step = normalizeCampaignStep(normalized.step);
   normalized.activeSaveSlot = normalizeSlot(normalized.activeSaveSlot);
   normalized.gold = normalizeNonNegativeInteger(normalized.gold);
   normalized.roster = arrayOrEmpty<UnitData>(normalized.roster).map(cloneUnit);
@@ -861,6 +874,10 @@ function normalizeReserveTrainingFocusId(focusId?: string): CampaignReserveTrain
     : defaultCampaignReserveTrainingFocusId;
 }
 
+function normalizeCampaignStep(step: unknown): CampaignStep {
+  return typeof step === 'string' && campaignStepIds.has(step as CampaignStep) ? step as CampaignStep : 'new';
+}
+
 function reserveTrainingFocusDefinition(focusId?: string) {
   const normalizedId = normalizeReserveTrainingFocusId(focusId);
   return campaignReserveTrainingFocusDefinitions.find((focus) => focus.id === normalizedId) ?? campaignReserveTrainingFocusDefinitions[0];