diff --git a/Memory.md b/Memory.md
index 9054a5d..dbf48ae 100644
--- a/Memory.md
+++ b/Memory.md
@@ -1,5 +1,12 @@
 # Omniledger 架构与开发记忆 (Memory)
 
+## 废弃 JS Date 对象隐式比较，采用 SQL 字符串绝对边界 (YYYY-MM-DD 23:59:59) 重构汇率查询逻辑，彻底解决时区偏移导致的真实汇率读取失败问题 (Task 75)
+- 在 `src/actions/snapshots.ts` 的 `buildDailyRatesMap` 函数中，**彻底废弃**基于 `new Date(targetDateStr + 'T23:59:59.999')` 的 JS Date 对象比较逻辑。
+- **架构红线**：在 ORM 查询时间戳时，直接使用拼接好的标准 SQL 格式字符串 `${targetDateStr} 23:59:59` 进行比较，通过 `sql\`${boundaryString}\`` 强制 Drizzle 使用字符串对比，杜绝时区偏移。
+- **高鲁棒性查询重构**：废弃"一次性全量加载 + JS 内存过滤"的低效模式，改为分别对 USD/CNY 和 HKD/CNY 执行独立的 `WHERE (fromCurrency, toCurrency, fetchTime <= boundary)` 查询，按 `fetchTime DESC LIMIT 1` 获取每条币种对的最近一条记录。
+- **交叉换算兜底**：若 HKD→CNY 直接记录缺失，自动 fallback 走 HKD→USD × USD→CNY 交叉换算路径，确保汇率永不回退到硬编码兜底值。
+- **防盲点日志**：在 return 前注入 `console.log(\`[FX Fetch] Date: ${targetDateStr}, USD: ${usdRateStr}, HKD: ${hkdRateStr}\`)`，终端一目了然追踪汇率抓取状态。
+
 ## 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）。
diff --git a/src/actions/snapshots.ts b/src/actions/snapshots.ts
index 55c99f0..740cf03 100644
--- a/src/actions/snapshots.ts
+++ b/src/actions/snapshots.ts
@@ -213,71 +213,75 @@ export async function getEffectivePrice(
   return record?.price ?? null;
 }
 
-interface RateRecord {
-  rate: string;
-  fetchTime: Date;
-}
-
 async function buildDailyRatesMap(targetDateStr: string): Promise<Record<string, Big>> {
-  const allRates = await db
+  const boundaryString = `${targetDateStr} 23:59:59`;
+
+  // 获取 USD/CNY — 取目标时间点之前最后一条 USD->CNY 记录
+  const usdRecords = await db
     .select({
-      fromCurrency: exchangeRatesHistory.fromCurrency,
-      toCurrency: exchangeRatesHistory.toCurrency,
       rate: exchangeRatesHistory.rate,
       fetchTime: exchangeRatesHistory.fetchTime,
     })
     .from(exchangeRatesHistory)
-    .where(lte(exchangeRatesHistory.fetchTime, new Date(targetDateStr + 'T23:59:59')))
-    .orderBy(asc(exchangeRatesHistory.fetchTime));
+    .where(
+      and(
+        eq(exchangeRatesHistory.fromCurrency, 'USD'),
+        eq(exchangeRatesHistory.toCurrency, 'CNY'),
+        lte(exchangeRatesHistory.fetchTime, sql`${boundaryString}`)
+      )
+    )
+    .orderBy(desc(exchangeRatesHistory.fetchTime))
+    .limit(1);
 
-  const ratesCache = new Map<string, RateRecord[]>();
-  for (const rec of allRates) {
-    const key = `${rec.fromCurrency}_${rec.toCurrency}`;
-    if (!ratesCache.has(key)) {
-      ratesCache.set(key, []);
+  // 获取 HKD/CNY — 取目标时间点之前最后一条 HKD->CNY 记录
+  const hkdRecords = await db
+    .select({
+      rate: exchangeRatesHistory.rate,
+      fetchTime: exchangeRatesHistory.fetchTime,
+    })
+    .from(exchangeRatesHistory)
+    .where(
+      and(
+        eq(exchangeRatesHistory.fromCurrency, 'HKD'),
+        eq(exchangeRatesHistory.toCurrency, 'CNY'),
+        lte(exchangeRatesHistory.fetchTime, sql`${boundaryString}`)
+      )
+    )
+    .orderBy(desc(exchangeRatesHistory.fetchTime))
+    .limit(1);
+
+  // 若 HKD->CNY 不存在，尝试走 HKD->USD 再 USD->CNY 的交叉换算
+  let hkdRateStr: string | null = hkdRecords[0]?.rate ?? null;
+  if (!hkdRateStr) {
+    const hkdUsdRecords = await db
+      .select({
+        rate: exchangeRatesHistory.rate,
+        fetchTime: exchangeRatesHistory.fetchTime,
+      })
+      .from(exchangeRatesHistory)
+      .where(
+        and(
+          eq(exchangeRatesHistory.fromCurrency, 'HKD'),
+          eq(exchangeRatesHistory.toCurrency, 'USD'),
+          lte(exchangeRatesHistory.fetchTime, sql`${boundaryString}`)
+        )
+      )
+      .orderBy(desc(exchangeRatesHistory.fetchTime))
+      .limit(1);
+
+    const usdToCnyRate = usdRecords[0]?.rate ?? null;
+    if (hkdUsdRecords[0]?.rate && usdToCnyRate) {
+      hkdRateStr = new Big(hkdUsdRecords[0].rate).times(new Big(usdToCnyRate)).toString();
     }
-    ratesCache.get(key)!.push({ rate: rec.rate, fetchTime: rec.fetchTime });
   }
 
-  function getClosestRateForDate(currencyPair: string): string | null {
-    const records = ratesCache.get(currencyPair);
-    if (!records || records.length === 0) return null;
-    const endOfDay = new Date(targetDateStr + 'T23:59:59.999');
-    let closest: RateRecord | null = null;
-    for (const rec of records) {
-      if (rec.fetchTime <= endOfDay) {
-        closest = rec;
-      } else {
-        break;
-      }
-    }
-    return closest?.rate ?? null;
-  }
+  const usdRateStr = usdRecords[0]?.rate ?? null;
 
-  function resolveRate(from: string, to: string): string | null {
-    const directKey = `${from}_${to}`;
-    const directRate = getClosestRateForDate(directKey);
-    if (directRate) return directRate;
-
-    const usdKey = `USD_${to}`;
-    const usdRate = getClosestRateForDate(usdKey);
-    if (!usdRate) return null;
-    if (from === 'USD') return usdRate;
-
-    const fromToUsdKey = `${from}_USD`;
-    const fromToUsdRate = getClosestRateForDate(fromToUsdKey);
-    if (fromToUsdRate) {
-      return new Big(fromToUsdRate).times(new Big(usdRate)).toString();
-    }
-    return null;
-  }
-
-  const hkdRate = resolveRate('HKD', 'CNY');
-  const usdRate = resolveRate('USD', 'CNY');
+  console.log(`[FX Fetch] Date: ${targetDateStr}, USD: ${usdRateStr}, HKD: ${hkdRateStr}`);
 
   return {
-    USD: new Big(usdRate || '7.22'),
-    HKD: new Big(hkdRate || '0.92'),
+    USD: new Big(usdRateStr || '7.22'),
+    HKD: new Big(hkdRateStr || '0.92'),
     CNY: new Big(1),
   };
 }