fix(ledger): 修复历史净值双重汇率折算 bug 与汇率时间查询边界

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);