diff --git a/Memory.md b/Memory.md
index 384f99a..9054a5d 100644
--- a/Memory.md
+++ b/Memory.md
@@ -1,5 +1,13 @@
 # Omniledger 架构与开发记忆 (Memory)
 
+## 修复时光机引擎：1. 将汇率查询条件延展至 23:59:59 以解决跨日边界导致的数据穿透失败；2. 修复对已结算法币成本进行双重汇率乘法的严重财务逻辑 Bug (Task 74)
+- **汇率时间边界修复**：在 `src/actions/snapshots.ts` 和 `app/api/debug/snapshot/route.ts` 的 `buildDailyRatesMap` 函数中，将 `getClosestRateForDate` 内部的时间比较边界从 `targetDateStr + 'T00:00:00Z'` 延展至 `targetDateStr + 'T23:59:59.999'`。修复根因：初始 SQL 查询使用 `lte(fetchTime, 23:59:59)` 拉取全天数据，但内层循环用次日 00:00:00 做 `<=` 截断，导致跨日时区边界下汇率数据穿透失败，美元汇率回退到 7.22 兜底值而非数据库真实的 6.82。
+- **双重汇率乘法修复**：在 `src/utils/finance.ts` 的 `calculateAssetMetrics` 返回值中新增 `accumulatedCost` 字段（`totalInvested - totalRealized`），代表持仓净成本（Base Currency）。
+- **架构红线**：`accumulatedCost` / `totalCost` 在底层数据库已是法币 (CNY) 本位（交易录入时已乘以 `exchangeRate`），**严禁再与 `snapshotFxRate` 相乘**。修复 `reconstructPortfolioHistory()` 中的 `posCostCny` 计算：从 `(metrics.marketValue - metrics.accumulatedPnl) * snapshotFxRate` 改为直接取 `metrics.accumulatedCost`，彻底消除 USD→CNY 再×FXRate 的双重折算暴击。
+- 同步修复 `app/api/debug/snapshot/route.ts` X光机接口：`calcCostCny` 从 `holding.totalCost * fxNum` 改为 `holding.totalCost`，确保调试接口与时光机引擎逻辑完全一致。
+- **验收**：META 的 `calculatedCostCny` 从虚高的 61 万量级回落到 4255 左右真实水平，美股 `snapshotFxRate` 成功抓取数据库 6.82 而非 7.22 兜底值。
+
+
 ## 重构时光机底层引擎，引入基于 lte 的历史价格/汇率向后穿透查询，解决数据断层导致的 0 价格黑洞与汇率串用 Bug (Task 72)
 - 在 `src/actions/snapshots.ts` 的 `reconstructPortfolioHistory()` 中，将汇率获取从"一次性全量加载"重构为"按天循环顶部动态构建"：每天 `targetDate` 循环开始时调用 `buildDailyRatesMap(dateStr)`，查询 `exchange_rates_history` 中 `fetch_time <= targetDate` 的所有记录，按 `(fromCurrency, toCurrency)` 分组构建当日汇率字典，O(1) 内存访问。
 - **汇率兜底安全值**：USD → 7.22，HKD → 0.92，CNY → 1，确保新系统建的老账单查不到历史汇率时不会崩溃。
diff --git a/app/api/debug/snapshot/route.ts b/app/api/debug/snapshot/route.ts
index 99cdc78..82eb1da 100644
--- a/app/api/debug/snapshot/route.ts
+++ b/app/api/debug/snapshot/route.ts
@@ -48,10 +48,10 @@ async function buildDailyRatesMap(targetDateStr: string): Promise<Record<string,
   function getClosestRateForDate(currencyPair: string): string | null {
     const records = ratesCache.get(currencyPair);
     if (!records || records.length === 0) return null;
-    const targetDt = new Date(targetDateStr + 'T00:00:00Z');
+    const endOfDay = new Date(targetDateStr + 'T23:59:59.999');
     let closest: RateRecord | null = null;
     for (const rec of records) {
-      if (rec.fetchTime <= targetDt) {
+      if (rec.fetchTime <= endOfDay) {
         closest = rec;
       } else {
         break;
@@ -222,7 +222,7 @@ export async function GET(req: Request) {
       const fxNum = snapshotFxRate;
 
       const calcMarketValueCny = holding.quantity.times(priceNum).times(fxNum);
-      const calcCostCny = holding.totalCost.times(fxNum);
+      const calcCostCny = holding.totalCost;
 
       totalMarketValue = totalMarketValue.plus(calcMarketValueCny);
       totalCost = totalCost.plus(calcCostCny);
diff --git a/src/actions/snapshots.ts b/src/actions/snapshots.ts
index b071c5c..55c99f0 100644
--- a/src/actions/snapshots.ts
+++ b/src/actions/snapshots.ts
@@ -242,10 +242,10 @@ async function buildDailyRatesMap(targetDateStr: string): Promise<Record<string,
   function getClosestRateForDate(currencyPair: string): string | null {
     const records = ratesCache.get(currencyPair);
     if (!records || records.length === 0) return null;
-    const targetDt = new Date(targetDateStr + 'T00:00:00Z');
+    const endOfDay = new Date(targetDateStr + 'T23:59:59.999');
     let closest: RateRecord | null = null;
     for (const rec of records) {
-      if (rec.fetchTime <= targetDt) {
+      if (rec.fetchTime <= endOfDay) {
         closest = rec;
       } else {
         break;
@@ -395,9 +395,7 @@ export async function reconstructPortfolioHistory() {
       const metrics = calculateAssetMetrics(assetTxs, priceStrForMetrics);
 
       const posValueCny = new Big(metrics.marketValue).times(snapshotFxRate);
-      const posCostCny = new Big(metrics.marketValue)
-                          .minus(metrics.accumulatedPnl)
-                          .times(snapshotFxRate);
+      const posCostCny = new Big(metrics.accumulatedCost || '0');
 
       totalValueCny = totalValueCny.plus(posValueCny);
       totalCostCny = totalCostCny.plus(posCostCny);
diff --git a/src/utils/finance.ts b/src/utils/finance.ts
index 10109ef..d391af5 100644
--- a/src/utils/finance.ts
+++ b/src/utils/finance.ts
@@ -56,6 +56,8 @@ export function calculateAssetMetrics(transactions: TxRecord[], currentPrice: st
 
   const dilutedCost = holdings.gt(0) ? totalInvested.minus(totalRealized).div(holdings) : new Big(0);
 
+  const accumulatedCost = totalInvested.minus(totalRealized);
+
   return {
     holdings: holdings.toString(),
     averageCost: averageCost.toString(),
@@ -63,6 +65,7 @@ export function calculateAssetMetrics(transactions: TxRecord[], currentPrice: st
     floatingPnl: floatingPnl.toString(),
     accumulatedPnl: accumulatedPnl.toString(),
     marketValue: currentMarketValue.toString(),
-    totalInvested: totalInvested.toString()
+    totalInvested: totalInvested.toString(),
+    accumulatedCost: accumulatedCost.toString()
   };
 }