fix(core): 明细用量美元保留 6 位小数

packages/core/src/money.ts

@@ -18,6 +18,15 @@ export function microUsdToQuotaUsdStr(micro: number): string {
   return `${dollars}.${String(rem).padStart(2, "0")}`;
 }
 
+/** 明细行等小额场景：保留更多小数位（默认 4 位，仍是字符串两位小数契约的展示增强） */
+export function microUsdToQuotaUsdStrPrecise(
+  micro: number,
+  fractionDigits = 4,
+): string {
+  const usd = micro / 1_000_000;
+  return usd.toFixed(fractionDigits);
+}
+
 export function quotaToUsdStr(quota: number, qpu: number): string {
   return microUsdToQuotaUsdStr(quotaToMicroUsd(quota, qpu));
 }

packages/core/src/usage.ts

@@ -3,6 +3,7 @@
  */
 import {
   microSumToUsdStr,
+  microUsdToQuotaUsdStrPrecise,
   qpuAt,
   quotaToMicroUsd,
   quotaToUsdStr,
@@ -54,6 +55,21 @@ export function usageAt(
   return { count: 1, quota, quota_usd: quotaToUsdStr(quota, qpu) };
 }
 
+/** 明细行：按当时 QPU 换算，展示保留 6 位小数（微美元级，小额不被抹成 0） */
+export function usageRowPrecise(
+  quota: number,
+  created_at: Date | number,
+  timeline: readonly QpuPoint[],
+): UsageSum {
+  const qpu = qpuAt(created_at, timeline);
+  const micro = quotaToMicroUsd(quota, qpu);
+  return {
+    count: 1,
+    quota,
+    quota_usd: microUsdToQuotaUsdStrPrecise(micro, 6),
+  };
+}
+
 export function addUsage(a: UsageSum, b: UsageSum): UsageSum {
   // 合并已成形的两段时，quota_usd 需重算——调用方应尽量走 sumUsage
   return {