haotool · s123104 · Jun 26, 2026 · Jun 26, 2026 · chatgpt-codex-connector · Jun 26, 2026
diff --git a/.changeset/split-meow-expense-currency-snapshot.md b/.changeset/split-meow-expense-currency-snapshot.md
@@ -0,0 +1,5 @@
+---
+'@app/split-meow': patch
+---
+
+每筆支出記錄記帳當下的幣別與匯率，切換顯示幣別後歷史金額不再被錯誤換算；以韓元（₩）記帳的支出會同時顯示對應的台幣參考金額。
diff --git a/apps/split-meow/src/components/HistoryTab.tsx b/apps/split-meow/src/components/HistoryTab.tsx
@@ -1,6 +1,7 @@
 import { useTranslation } from 'react-i18next';
 import { useStore, type Member, type ExpenseRecord } from '../store/useStore';
-import { formatAmount, getCurrencySymbol } from '../config/currencies';
+import { formatAmount, getCurrencySymbol, formatKrwAsTwd } from '../config/currencies';
+import type { CurrencyCode } from '../config/currencies';
 import { format } from 'date-fns';
 import { useRef, useState } from 'react';
 import { cn } from '../lib/utils';
@@ -177,6 +178,12 @@ export function HistoryTab() {
     });
   const totalSpent = tripExpenses.reduce((sum, e) => sum + e.totalAmount, 0);
 
+  // trip 主導幣別：採用該行程最舊一筆記錄的幣別（trip 建立時的幣別），
+  // 舊資料無幣別時 fallback 至當前全域幣別。彙總與結算統一以此幣別顯示。
+  const tripCurrency: CurrencyCode = tripExpenses[tripExpenses.length - 1]?.currency ?? currency;
+  // 取得單筆記錄的顯示幣別（優先使用記帳當下快照，舊資料 fallback 主導幣別）。
+  const expenseCurrency = (exp: ExpenseRecord): CurrencyCode => exp.currency ?? tripCurrency;
+
   // 計算各人餘額
   const balances: Record<string, number> = {};
   tripExpenses.forEach((exp) => {
@@ -215,7 +222,7 @@ export function HistoryTab() {
     const lines: string[] = [
       `🐾 喵喵分帳 — ${tripName}`,
       `${'─'.repeat(24)}`,
-      `💰 總花費：${formatAmount(totalSpent, currency)}`,
+      `💰 總花費：${formatAmount(totalSpent, tripCurrency)}`,
       '',
     ];
     if (tripExpenses.length > 0) {
@@ -226,7 +233,9 @@ export function HistoryTab() {
         const label =
           exp.note ||
           (exp.type === 'split_evenly' ? t('history.split_evenly') : t('history.itemized'));
-        lines.push(`${emoji} ${label}  ${formatAmount(exp.totalAmount, currency)}（${payer} 付）`);
+        lines.push(
+          `${emoji} ${label}  ${formatAmount(exp.totalAmount, expenseCurrency(exp))}（${payer} 付）`,
+        );
       });
       lines.push('');
     }
@@ -235,7 +244,7 @@ export function HistoryTab() {
       settlements.forEach((s) => {
         const from = members.find((m) => m.id === s.from)?.name ?? s.from;
         const to = members.find((m) => m.id === s.to)?.name ?? s.to;
-        lines.push(`${from} → ${to}  ${formatAmount(s.amount, currency)}`);
+        lines.push(`${from} → ${to}  ${formatAmount(s.amount, tripCurrency)}`);
       });
       lines.push('');
     }
@@ -273,7 +282,7 @@ export function HistoryTab() {
               {t('history.total_spent')}
             </span>
             <h2 className="text-4xl font-medium text-on-surface tracking-tight">
-              {formatAmount(totalSpent, currency)}
+              {formatAmount(totalSpent, tripCurrency)}
             </h2>
           </div>
           <div className="mt-6 flex items-center justify-between gap-2">
@@ -376,7 +385,7 @@ export function HistoryTab() {
                           check_circle
                         </span>
                       ) : (
-                        formatAmount(s.amount, currency)
+                        formatAmount(s.amount, tripCurrency)
                       )}
                     </span>
                   </div>
@@ -451,7 +460,7 @@ export function HistoryTab() {
                           )}
                         >
                           {isOwed ? '+' : '-'}
-                          {formatAmount(Math.abs(amount), currency)}
+                          {formatAmount(Math.abs(amount), tripCurrency)}
                         </span>
                         <span
                           className="material-symbols-outlined text-on-surface-variant text-lg transition-transform duration-300"
@@ -513,7 +522,7 @@ export function HistoryTab() {
                                     {t('history.balance_paid')}
                                   </span>
                                   <span className="font-semibold text-secondary">
-                                    +{formatAmount(exp.totalAmount, currency)}
+                                    +{formatAmount(exp.totalAmount, expenseCurrency(exp))}
                                   </span>
                                 </div>
                               )}
@@ -528,7 +537,7 @@ export function HistoryTab() {
                                     {t('history.balance_share')}
                                   </span>
                                   <span className="font-semibold text-error">
-                                    -{formatAmount(share, currency)}
+                                    -{formatAmount(share, expenseCurrency(exp))}
                                   </span>
                                 </div>
                               )}
@@ -549,7 +558,7 @@ export function HistoryTab() {
                                   )}
                                 >
                                   {net > 0.01 ? '+' : net < -0.01 ? '-' : ''}
-                                  {formatAmount(Math.abs(net), currency)}
+                                  {formatAmount(Math.abs(net), expenseCurrency(exp))}
                                 </span>
                               </div>
                             </div>
@@ -568,7 +577,7 @@ export function HistoryTab() {
                             )}
                           >
                             {isOwed ? '+' : '-'}
-                            {formatAmount(Math.abs(amount), currency)}
+                            {formatAmount(Math.abs(amount), tripCurrency)}
                           </span>
                         </div>
                       </div>
@@ -708,8 +717,14 @@ export function HistoryTab() {
                       <div className="text-right flex items-center gap-2 sm:gap-3 shrink-0">
                         <div className="shrink-0">
                           <p className="font-bold text-on-surface whitespace-nowrap text-base sm:text-lg">
-                            {formatAmount(exp.totalAmount, currency)}
+                            {formatAmount(exp.totalAmount, expenseCurrency(exp))}
                           </p>
+                          {expenseCurrency(exp) === 'KRW' &&
+                            formatKrwAsTwd(exp.totalAmount, exp.exchangeRateKrwPerTwd) && (
+                              <p className="text-[10px] font-medium text-on-surface-variant/70 whitespace-nowrap">
+                                ≈ {formatKrwAsTwd(exp.totalAmount, exp.exchangeRateKrwPerTwd)}
+                              </p>
+                            )}
                           <p className="text-[10px] font-medium text-secondary uppercase tracking-wider">
                             {t('history.participants', { count: exp.participantIds.length })}
                           </p>
@@ -830,7 +845,7 @@ export function HistoryTab() {
                                   <span className="font-medium text-on-surface">{m.name}</span>
                                 </div>
                                 <span className="font-semibold text-on-surface">
-                                  {formatAmount(amt, currency)}
+                                  {formatAmount(amt, expenseCurrency(exp))}
                                 </span>
                               </div>
                             );

diff --git a/apps/split-meow/src/config/__tests__/currencies.test.ts b/apps/split-meow/src/config/__tests__/currencies.test.ts
@@ -1,5 +1,10 @@
 import { describe, it, expect } from 'vitest';
-import { formatAmount, detectCurrencyFromTimezone, getCurrencySymbol } from '../currencies';
+import {
+  formatAmount,
+  detectCurrencyFromTimezone,
+  getCurrencySymbol,
+  formatKrwAsTwd,
+} from '../currencies';
 
 describe('formatAmount', () => {
   it('TWD：以 NT$ 前綴格式化', () => {
@@ -59,3 +64,23 @@ describe('detectCurrencyFromTimezone', () => {
     expect(detectCurrencyFromTimezone()).toBeNull();
   });
 });
+
+describe('formatKrwAsTwd', () => {
+  it('依匯率將 KRW 換算為 TWD 顯示字串', () => {
+    // 30000 KRW / 43.5 (KRW per TWD) ≈ 689.66 → NT$ 690
+    expect(formatKrwAsTwd(30000, 43.5)).toBe('NT$ 690');
+  });
+
+  it('匯率為 null 時回傳 null（無法換算）', () => {
+    expect(formatKrwAsTwd(30000, null)).toBeNull();
+  });
+
+  it('匯率為 0 或負值時回傳 null（避免除以零）', () => {
+    expect(formatKrwAsTwd(30000, 0)).toBeNull();
+    expect(formatKrwAsTwd(30000, -1)).toBeNull();
+  });
+
+  it('匯率為 undefined（舊資料）時回傳 null', () => {
+    expect(formatKrwAsTwd(30000, undefined)).toBeNull();
+  });
+});
diff --git a/apps/split-meow/src/config/currencies.ts b/apps/split-meow/src/config/currencies.ts
@@ -36,3 +36,12 @@ export function formatAmount(amount: number, currency: CurrencyCode): string {
 export function getCurrencySymbol(currency: CurrencyCode): string {
   return CURRENCIES[currency].symbol;
 }
+
+/**
+ * 將 KRW 金額依匯率快照換算為 TWD 顯示字串（用於 KRW 記帳時的副標）。
+ * rate 為 1 TWD = rate KRW（賣出價）；rate 無效時回傳 null 表示無法換算。
+ */
+export function formatKrwAsTwd(krwAmount: number, rate: number | null | undefined): string | null {
+  if (typeof rate !== 'number' || !Number.isFinite(rate) || rate <= 0) return null;
+  return formatAmount(krwAmount / rate, 'TWD');
+}
diff --git a/apps/split-meow/src/store/__tests__/useStore.test.ts b/apps/split-meow/src/store/__tests__/useStore.test.ts
@@ -207,6 +207,23 @@ describe('useStore', () => {
       expect(useStore.getState().activeTab).toBe('history');
     });
 
+    it('保存記帳當下的幣別與匯率快照（KRW）', () => {
+      useStore.setState({ calculatorValue: '30000', currency: 'KRW', krwPerTwd: 43.5 });
+      act(() => useStore.getState().saveExpense());
+      const exp = useStore.getState().expenses[0]!;
+      expect(exp.currency).toBe('KRW');
+      expect(exp.exchangeRateKrwPerTwd).toBe(43.5);
+    });
+
+    it('幣別快照不受日後切換幣別影響', () => {
+      useStore.setState({ calculatorValue: '1000', currency: 'TWD', krwPerTwd: null });
+      act(() => useStore.getState().saveExpense());
+      // 記帳後切換全域幣別到 KRW
+      act(() => useStore.getState().setCurrency('KRW'));
+      const exp = useStore.getState().expenses[0]!;
+      expect(exp.currency).toBe('TWD');
+    });
+
     it('儲存後清空計算機', () => {
       useStore.setState({ calculatorValue: '100', expenseNote: '午餐' });
       act(() => useStore.getState().saveExpense());

diff --git a/apps/split-meow/src/store/useStore.ts b/apps/split-meow/src/store/useStore.ts
@@ -32,6 +32,10 @@ export interface ExpenseRecord {
   note: string;
   category?: ExpenseCategory;
   createdAt: number;
+  /** 記帳當下的幣別快照；舊資料缺此欄位時視為 TWD（記帳幣別於 KRW 上線前僅有 TWD）。 */
+  currency?: CurrencyCode;
+  /** 記帳當下的匯率快照（1 TWD = X KRW 賣出價）；供 KRW 金額回溯換算 TWD，舊資料為 null。 */
+  exchangeRateKrwPerTwd?: number | null;
 }
 
 export interface Trip {
@@ -266,6 +270,9 @@ export const useStore = create<AppState>()(
             note: state.expenseNote.trim(),
             ...(state.expenseCategory ? { category: state.expenseCategory } : {}),
             createdAt: Date.now(),
+            // 記帳當下的幣別與匯率快照，確保歷史金額不受日後切換幣別影響並可回溯換算
+            currency: state.currency,
+            exchangeRateKrwPerTwd: state.krwPerTwd,
           };
 
           return {

diff --git a/docs/dev/002_development_reward_penalty_log.md b/docs/dev/002_development_reward_penalty_log.md
@@ -2,7 +2,7 @@
 
 > 版本：outline-v2-ultra
 > 原則：每筆只保留日期、ID、原因、解法。
-> 本次分數變化：+1（reward 1、penalty 0）｜累計總分：+66
+> 本次分數變化：+2（reward 2、penalty 0）｜累計總分：+68
 
 ## 新增模板（4 行）
 
@@ -13,6 +13,16 @@
 
 ## 條目（新→舊）
 
+- 日期：2026-06-26
+- ID：reward-split-meow-expense-currency-rate-snapshot
+- 原因：split-meow 的 ExpenseRecord 只存裸數字、未保存記帳當下幣別；使用者先以 TWD 記帳後切換 KRW（或韓國時區自動偵測）時，歷史金額會被當前全域幣別重新格式化，NT$1,000 被誤顯示為 ₩1,000。
+- 解法：ExpenseRecord 增加 currency 與 exchangeRateKrwPerTwd 快照欄位，記帳時保存；HistoryTab 個別金額改用各筆快照幣別、KRW 副標即時換算 TWD、彙總/結算採 trip 主導幣別 fallback；補 store/currencies 單元測試與 Playwright 瀏覽器驗收（切回 TWD 後 KRW 記錄仍正確）。
+
+- 日期：2026-06-26
+- ID：reward-pr426-sw-bounded-nav-case3-002-audit
+- 原因：PR 426 review P1 指出 SW case-3 有界網路 fallback 與測試 lint 修改的 commit 未含 002 稽核軌跡；該功能已隨 #433 生產治理進 main，但稽核條目隨被取代的 #411 分支遺失。
+- 解法：補本條目搶救稽核軌跡；SW case-3 setCatchHandler 有界 fallback 本體已於 #433 收斂進 main。
+
 - 日期：2026-06-26
 - ID：reward-pr435-code-reviewer-hardening
 - 原因：Codex 配額用盡無法 review PR 435，改派 code-reviewer 代理把關，發現 i18n 探測在 removeItem 丟錯時會誤判 localStorage 不可寫（可寫性結論不應依賴清除步驟），且 smoke 測試 BASE_STATE 仍缺部分 test-mutable 欄位。