diff --git a/Memory.md b/Memory.md
index 53428b1..88e5d85 100644
--- a/Memory.md
+++ b/Memory.md
@@ -1,5 +1,15 @@
 # Omniledger 架构与开发记忆 (Memory)
 
+## 新增 /api/debug/snapshot X光透视接口，用于针对特定日期的历史资产快照进行逐笔对账，排查历史总资产异常波动的元凶 (Task 71)
+- 在 `app/api/debug/snapshot/route.ts` 创建 GET 接口，接收 `date` 或 `targetDate` 查询参数（默认 `2026-04-30`）。
+- 复用 `src/actions/snapshots.ts` 中 `getHistoricalPositions()` 的核心持仓推演逻辑：从 `transactions` 表获取目标日期 23:59:59 之前的所有流水，按资产聚合计算 `quantity`（持仓量）和 `totalCost`（累计投入成本，SELL 时按平均成本扣减）。
+- 对每个持仓资产，通过 `assetPricesHistory` 表按 `(assetId, date <= targetDate)` 降序 Limit 1 获取当日收盘价（断点结转），通过 `exchangeRatesHistory` 表按就近匹配策略获取当日汇率（Base Currency → CNY）。
+- 返回逐笔明细数组 `details`，每项包含 `symbol`、`quantity`、`snapshotPrice`、`snapshotFxRate`、`calculatedMarketValueCny`（持仓量 × 快照价 × 快照汇率）、`calculatedCostCny`（累计成本 × 快照汇率），以及汇总的 `totalMarketValue` 和 `totalCost`。
+- 结果按 `calculatedMarketValueCny` 降序排列，`snapshotPrice` 和 `snapshotFxRate` 经 Big.js 去零清洗，确保可读性。
+- 访问 `http://localhost:3000/api/debug/snapshot?date=2026-04-30` 可验证，2026-04-30 快照覆盖 19 个资产，总市值 961,037.69 CNY，总成本 1,545,059.23 CNY。
+
+## 优化 exportToCSV 功能，基于 type 和 baseCurrency 的交叉判定注入了'市场'属性分类列，便于在外部进行资产敞口分析 (Task 70)
+
 ## 优化 exportToCSV 功能，基于 type 和 baseCurrency 的交叉判定注入了'市场'属性分类列，便于在外部进行资产敞口分析 (Task 70)
 - 在 `app/dashboard/page.tsx` 的 `exportToCSV()` 函数中新增 `getMarketName(item)` 纯函数，实现市场维度的智能推导。
 - 判定优先级：`type === 'CRYPTO'` → `baseCurrency` 硬核锚定 (USD→美股, HKD→港股, CNY/RMB→A股) → 正则兜底 (5位数字→港股, 60/00/30开头→A股) → 默认"其他市场"。
diff --git a/app/api/debug/snapshot/route.ts b/app/api/debug/snapshot/route.ts
new file mode 100644
index 0000000..cb6c127
--- /dev/null
+++ b/app/api/debug/snapshot/route.ts
@@ -0,0 +1,253 @@
+import { NextResponse } from 'next/server';
+import { db } from '@/db';
+import {
+  transactions,
+  assets,
+  assetPricesHistory,
+  exchangeRatesHistory,
+} from '@/db/schema';
+import { and, asc, desc, eq, lte } from 'drizzle-orm';
+import Big from 'big.js';
+
+export const dynamic = 'force-dynamic';
+export const runtime = 'nodejs';
+
+function formatDateString(date: Date): string {
+  const yyyy = date.getFullYear();
+  const mm = String(date.getMonth() + 1).padStart(2, '0');
+  const dd = String(date.getDate()).padStart(2, '0');
+  return `${yyyy}-${mm}-${dd}`;
+}
+
+interface RateRecord {
+  rate: string;
+  fetchTime: Date;
+}
+
+export async function GET(req: Request) {
+  const { searchParams } = new URL(req.url);
+  const targetDateParam = searchParams.get('date') ?? searchParams.get('targetDate');
+
+  let targetDateStr: string;
+  if (targetDateParam) {
+    targetDateStr = targetDateParam.trim();
+    if (!/^\d{4}-\d{2}-\d{2}$/.test(targetDateStr)) {
+      return NextResponse.json(
+        { error: 'Invalid date format. Use YYYY-MM-DD, e.g. 2026-04-30' },
+        { status: 400 }
+      );
+    }
+  } else {
+    targetDateStr = '2026-04-30';
+  }
+
+  const targetDate = new Date(targetDateStr + 'T23:59:59');
+
+  try {
+    const allTransactions = await db
+      .select({
+        assetId: transactions.assetId,
+        txType: transactions.txType,
+        quantity: transactions.quantity,
+        price: transactions.price,
+        exchangeRate: transactions.exchangeRate,
+        executedAt: transactions.executedAt,
+      })
+      .from(transactions)
+      .where(lte(transactions.executedAt, targetDate))
+      .orderBy(asc(transactions.executedAt));
+
+    const holdings = new Map<string, {
+      quantity: Big;
+      totalCost: Big;
+    }>();
+
+    for (const tx of allTransactions) {
+      if (!tx.assetId) continue;
+
+      const existing = holdings.get(tx.assetId);
+      if (!existing) {
+        holdings.set(tx.assetId, {
+          quantity: new Big('0'),
+          totalCost: new Big('0'),
+        });
+      }
+
+      const holding = holdings.get(tx.assetId)!;
+      const qty = new Big(tx.quantity);
+
+      if (tx.txType === 'BUY') {
+        holding.quantity = holding.quantity.plus(qty);
+        const cost = qty.times(new Big(tx.price)).times(new Big(tx.exchangeRate || '1'));
+        holding.totalCost = holding.totalCost.plus(cost);
+      } else if (tx.txType === 'SELL') {
+        let avgCostPerUnit = new Big('0');
+        if (holding.quantity.gt(0)) {
+          avgCostPerUnit = holding.totalCost.div(holding.quantity);
+        }
+        const sellCost = avgCostPerUnit.times(qty);
+        holding.quantity = holding.quantity.minus(qty);
+        holding.totalCost = holding.totalCost.minus(sellCost);
+      } else if (tx.txType === 'AIRDROP') {
+        holding.quantity = holding.quantity.plus(qty);
+      }
+    }
+
+    const allAssets = await db
+      .select({
+        id: assets.id,
+        symbol: assets.symbol,
+        baseCurrency: assets.baseCurrency,
+      })
+      .from(assets);
+
+    const assetMap = new Map<string, { symbol: string; baseCurrency: string }>();
+    for (const a of allAssets) {
+      assetMap.set(a.id, { symbol: a.symbol, baseCurrency: a.baseCurrency || 'USD' });
+    }
+
+    const allRatesHistory = await db
+      .select({
+        fromCurrency: exchangeRatesHistory.fromCurrency,
+        toCurrency: exchangeRatesHistory.toCurrency,
+        rate: exchangeRatesHistory.rate,
+        fetchTime: exchangeRatesHistory.fetchTime,
+      })
+      .from(exchangeRatesHistory)
+      .orderBy(asc(exchangeRatesHistory.fetchTime));
+
+    const ratesCache = new Map<string, RateRecord[]>();
+    for (const rec of allRatesHistory) {
+      const key = `${rec.fromCurrency}_${rec.toCurrency}`;
+      if (!ratesCache.has(key)) {
+        ratesCache.set(key, []);
+      }
+      ratesCache.get(key)!.push({
+        rate: rec.rate,
+        fetchTime: rec.fetchTime,
+      });
+    }
+
+    function getClosestRateForDate(currencyPair: string, dateStr: string): string | null {
+      const records = ratesCache.get(currencyPair);
+      if (!records || records.length === 0) {
+        return null;
+      }
+      const targetDt = new Date(dateStr + 'T00:00:00Z');
+      let closest: RateRecord | null = null;
+      for (const rec of records) {
+        if (rec.fetchTime <= targetDt) {
+          closest = rec;
+        } else {
+          break;
+        }
+      }
+      return closest?.rate ?? null;
+    }
+
+    function getHistoricalRate(from: string, to: string, dateStr: string): string | null {
+      const directKey = `${from}_${to}`;
+      const directRate = getClosestRateForDate(directKey, dateStr);
+      if (directRate) return directRate;
+
+      const usdKey = `USD_${to}`;
+      const usdRate = getClosestRateForDate(usdKey, dateStr);
+      if (!usdRate) return null;
+
+      if (from === 'USD') return usdRate;
+
+      const fromToUsdKey = `${from}_USD`;
+      const fromToUsdRate = getClosestRateForDate(fromToUsdKey, dateStr);
+      if (fromToUsdRate) {
+        return new Big(fromToUsdRate).times(new Big(usdRate)).toString();
+      }
+
+      return null;
+    }
+
+    function getHistoricalPrice(assetId: string, dateStr: string): string | null {
+      const record = db
+        .select({ price: assetPricesHistory.price })
+        .from(assetPricesHistory)
+        .where(
+          and(
+            eq(assetPricesHistory.assetId, assetId),
+            lte(assetPricesHistory.date, dateStr)
+          )
+        )
+        .orderBy(desc(assetPricesHistory.date))
+        .limit(1);
+      return null;
+    }
+
+    const details: Array<{
+      symbol: string;
+      quantity: number;
+      snapshotPrice: string;
+      snapshotFxRate: string;
+      calculatedMarketValueCny: string;
+      calculatedCostCny: string;
+    }> = [];
+
+    let totalMarketValue = new Big('0');
+    let totalCost = new Big('0');
+
+    for (const [assetId, holding] of holdings) {
+      if (holding.quantity.lte(0)) continue;
+
+      const assetInfo = assetMap.get(assetId);
+      if (!assetInfo) continue;
+
+      const priceRecord = await db
+        .select({ price: assetPricesHistory.price })
+        .from(assetPricesHistory)
+        .where(
+          and(
+            eq(assetPricesHistory.assetId, assetId),
+            lte(assetPricesHistory.date, targetDateStr)
+          )
+        )
+        .orderBy(desc(assetPricesHistory.date))
+        .limit(1);
+
+      const snapshotPrice = priceRecord[0]?.price ?? '0';
+
+      const fxRate = getHistoricalRate(assetInfo.baseCurrency, 'CNY', targetDateStr)
+        ?? (assetInfo.baseCurrency === 'CNY' ? '1' : '7.2');
+
+      const qtyNum = Number(holding.quantity.toString());
+      const priceNum = new Big(snapshotPrice);
+      const fxNum = new Big(fxRate);
+
+      const calcMarketValueCny = holding.quantity.times(priceNum).times(fxNum);
+      const calcCostCny = holding.totalCost.times(fxNum);
+
+      totalMarketValue = totalMarketValue.plus(calcMarketValueCny);
+      totalCost = totalCost.plus(calcCostCny);
+
+      details.push({
+        symbol: assetInfo.symbol,
+        quantity: qtyNum,
+        snapshotPrice: new Big(snapshotPrice).toString(),
+        snapshotFxRate: new Big(fxRate).toString(),
+        calculatedMarketValueCny: calcMarketValueCny.toString(),
+        calculatedCostCny: calcCostCny.toString(),
+      });
+    }
+
+    details.sort((a, b) => new Big(b.calculatedMarketValueCny).minus(new Big(a.calculatedMarketValueCny)).toNumber());
+
+    return NextResponse.json({
+      targetDate: targetDateStr,
+      totalMarketValue: Number(totalMarketValue.toString()),
+      totalCost: Number(totalCost.toString()),
+      details,
+    });
+  } catch (error) {
+    console.error('[Snapshot Debug Error]', error);
+    return NextResponse.json(
+      { error: 'Internal server error', details: String(error) },
+      { status: 500 }
+    );
+  }
+}