feat: add playable inter-battle city stays

src/game/state/campaignState.ts

@@ -1,6 +1,7 @@
 import { equipmentExpToNext, equipmentSlots, itemCatalog, type EquipmentSlot } from '../data/battleItems';
 import { unitClasses } from '../data/battleRules';
 import { battleScenarios, type BattleScenarioId } from '../data/battles';
+import { findCityStayAfterBattle, type CityStayId } from '../data/cityStays';
 import {
   campaignRecruitUnits,
   jianYongRecruitBond,
@@ -508,6 +509,7 @@ export type CampaignState = {
   battleHistory: Record<string, CampaignBattleSettlement>;
   latestBattleId?: string;
   pendingAftermathBattleId?: BattleScenarioId;
+  activeCityStayId?: CityStayId;
   firstBattleReport?: FirstBattleReport;
 };
 
@@ -808,6 +810,22 @@ export function listCampaignSaveSlots(): CampaignSaveSlotSummary[] {
 export function markCampaignStep(step: CampaignStep) {
   const state = ensureCampaignState();
   state.step = step;
+  if (!normalizeActiveCityStayId(state.activeCityStayId, state.latestBattleId, step)) {
+    delete state.activeCityStayId;
+  }
+  state.updatedAt = new Date().toISOString();
+  persistCampaignState(state);
+  return cloneCampaignState(state);
+}
+
+export function setActiveCityStayId(cityStayId?: CityStayId) {
+  const state = ensureCampaignState();
+  const normalizedCityStayId = normalizeActiveCityStayId(cityStayId, state.latestBattleId, state.step);
+  if (normalizedCityStayId) {
+    state.activeCityStayId = normalizedCityStayId;
+  } else {
+    delete state.activeCityStayId;
+  }
   state.updatedAt = new Date().toISOString();
   persistCampaignState(state);
   return cloneCampaignState(state);
@@ -1026,6 +1044,7 @@ export function setFirstBattleReport(report: FirstBattleReport) {
     }
     state.step = retryStep;
     state.latestBattleId = battleId;
+    delete state.activeCityStayId;
     delete state.pendingAftermathBattleId;
     state.updatedAt = new Date().toISOString();
     persistCampaignState(state);
@@ -1075,6 +1094,7 @@ export function setFirstBattleReport(report: FirstBattleReport) {
     delete state.sortieRecommendationSelection;
   }
   state.latestBattleId = battleId;
+  delete state.activeCityStayId;
   state.pendingAftermathBattleId = battleId as BattleScenarioId;
   state.updatedAt = new Date().toISOString();
 
@@ -1728,6 +1748,16 @@ function normalizeCampaignState(state: Partial<CampaignState>): CampaignState {
     );
   }
   normalized.latestBattleId = normalizeLatestBattleId(normalized.latestBattleId, normalized.battleHistory);
+  const activeCityStayId = normalizeActiveCityStayId(
+    normalized.activeCityStayId,
+    normalized.latestBattleId,
+    normalized.step
+  );
+  if (activeCityStayId) {
+    normalized.activeCityStayId = activeCityStayId;
+  } else {
+    delete normalized.activeCityStayId;
+  }
   const pendingAftermathBattleId = typeof normalized.pendingAftermathBattleId === 'string' &&
     normalized.pendingAftermathBattleId in battleScenarios
     ? normalized.pendingAftermathBattleId as BattleScenarioId
@@ -3228,6 +3258,27 @@ function cloneCampaignState(state: CampaignState): CampaignState {
   return JSON.parse(JSON.stringify(state)) as CampaignState;
 }
 
+function normalizeActiveCityStayId(
+  cityStayId: unknown,
+  latestBattleId: string | undefined,
+  step: CampaignStep
+): CityStayId | undefined {
+  if (typeof cityStayId !== 'string' || !latestBattleId || !isCampCampaignStep(step)) {
+    return undefined;
+  }
+  if (!(latestBattleId in battleScenarios)) {
+    return undefined;
+  }
+
+  const cityStay = findCityStayAfterBattle(latestBattleId as BattleScenarioId);
+  const expectedCampStep = cityStay
+    ? campaignBattleSteps[cityStay.afterBattleId]?.victory
+    : undefined;
+  return cityStay?.id === cityStayId && expectedCampStep === step
+    ? cityStay.id
+    : undefined;
+}
+
 function cloneReport(report: FirstBattleReport): FirstBattleReport {
   const cloned = JSON.parse(JSON.stringify(report)) as FirstBattleReport;
   cloned.itemRewards = normalizeRewardStrings(cloned.itemRewards);