fix(codex): 修复额度窗口过期展示并补齐高覆盖测试

- 后端新增绝对重置时间字段计算（codex_5h_reset_at/codex_7d_reset_at）

- 前端统一窗口解析逻辑：绝对时间优先，updated_at+seconds 回退，过期自动归零

- 新增后端与前端单元测试，覆盖关键边界与异常场景

frontend/src/utils/codexUsage.ts

@@ -0,0 +1,130 @@
+import type { CodexUsageSnapshot } from '@/types'
+
+export interface ResolvedCodexUsageWindow {
+  usedPercent: number | null
+  resetAt: string | null
+}
+
+type WindowKind = '5h' | '7d'
+
+function asNumber(value: unknown): number | null {
+  if (typeof value === 'number' && Number.isFinite(value)) return value
+  if (typeof value === 'string' && value.trim() !== '') {
+    const n = Number(value)
+    if (Number.isFinite(n)) return n
+  }
+  return null
+}
+
+function asString(value: unknown): string | null {
+  if (typeof value !== 'string') return null
+  const trimmed = value.trim()
+  return trimmed === '' ? null : trimmed
+}
+
+function asISOTime(value: unknown): string | null {
+  const raw = asString(value)
+  if (!raw) return null
+  const date = new Date(raw)
+  if (Number.isNaN(date.getTime())) return null
+  return date.toISOString()
+}
+
+function resolveLegacy5h(snapshot: Record<string, unknown>): { used: number | null; resetAfterSeconds: number | null } {
+  const primaryWindow = asNumber(snapshot.codex_primary_window_minutes)
+  const secondaryWindow = asNumber(snapshot.codex_secondary_window_minutes)
+  const primaryUsed = asNumber(snapshot.codex_primary_used_percent)
+  const secondaryUsed = asNumber(snapshot.codex_secondary_used_percent)
+  const primaryReset = asNumber(snapshot.codex_primary_reset_after_seconds)
+  const secondaryReset = asNumber(snapshot.codex_secondary_reset_after_seconds)
+
+  if (primaryWindow != null && primaryWindow <= 360) {
+    return { used: primaryUsed, resetAfterSeconds: primaryReset }
+  }
+  if (secondaryWindow != null && secondaryWindow <= 360) {
+    return { used: secondaryUsed, resetAfterSeconds: secondaryReset }
+  }
+  return { used: secondaryUsed, resetAfterSeconds: secondaryReset }
+}
+
+function resolveLegacy7d(snapshot: Record<string, unknown>): { used: number | null; resetAfterSeconds: number | null } {
+  const primaryWindow = asNumber(snapshot.codex_primary_window_minutes)
+  const secondaryWindow = asNumber(snapshot.codex_secondary_window_minutes)
+  const primaryUsed = asNumber(snapshot.codex_primary_used_percent)
+  const secondaryUsed = asNumber(snapshot.codex_secondary_used_percent)
+  const primaryReset = asNumber(snapshot.codex_primary_reset_after_seconds)
+  const secondaryReset = asNumber(snapshot.codex_secondary_reset_after_seconds)
+
+  if (primaryWindow != null && primaryWindow >= 10000) {
+    return { used: primaryUsed, resetAfterSeconds: primaryReset }
+  }
+  if (secondaryWindow != null && secondaryWindow >= 10000) {
+    return { used: secondaryUsed, resetAfterSeconds: secondaryReset }
+  }
+  return { used: primaryUsed, resetAfterSeconds: primaryReset }
+}
+
+function resolveFromSeconds(snapshot: Record<string, unknown>, resetAfterSeconds: number | null): string | null {
+  if (resetAfterSeconds == null) return null
+
+  const baseRaw = asString(snapshot.codex_usage_updated_at)
+  const base = baseRaw ? new Date(baseRaw) : new Date()
+  if (Number.isNaN(base.getTime())) {
+    return null
+  }
+
+  const sec = Math.max(0, resetAfterSeconds)
+  const resetAt = new Date(base.getTime() + sec * 1000)
+  return resetAt.toISOString()
+}
+
+function applyExpiredRule(window: ResolvedCodexUsageWindow, now: Date): ResolvedCodexUsageWindow {
+  if (window.usedPercent == null || !window.resetAt) return window
+  const resetDate = new Date(window.resetAt)
+  if (Number.isNaN(resetDate.getTime())) return window
+  if (resetDate.getTime() <= now.getTime()) {
+    return { usedPercent: 0, resetAt: resetDate.toISOString() }
+  }
+  return window
+}
+
+export function resolveCodexUsageWindow(
+  snapshot: (CodexUsageSnapshot & Record<string, unknown>) | null | undefined,
+  window: WindowKind,
+  now: Date = new Date()
+): ResolvedCodexUsageWindow {
+  if (!snapshot) {
+    return { usedPercent: null, resetAt: null }
+  }
+
+  const typedSnapshot = snapshot as Record<string, unknown>
+  let usedPercent: number | null
+  let resetAfterSeconds: number | null
+  let resetAt: string | null
+
+  if (window === '5h') {
+    usedPercent = asNumber(typedSnapshot.codex_5h_used_percent)
+    resetAfterSeconds = asNumber(typedSnapshot.codex_5h_reset_after_seconds)
+    resetAt = asISOTime(typedSnapshot.codex_5h_reset_at)
+    if (usedPercent == null || (resetAfterSeconds == null && !resetAt)) {
+      const legacy = resolveLegacy5h(typedSnapshot)
+      if (usedPercent == null) usedPercent = legacy.used
+      if (resetAfterSeconds == null) resetAfterSeconds = legacy.resetAfterSeconds
+    }
+  } else {
+    usedPercent = asNumber(typedSnapshot.codex_7d_used_percent)
+    resetAfterSeconds = asNumber(typedSnapshot.codex_7d_reset_after_seconds)
+    resetAt = asISOTime(typedSnapshot.codex_7d_reset_at)
+    if (usedPercent == null || (resetAfterSeconds == null && !resetAt)) {
+      const legacy = resolveLegacy7d(typedSnapshot)
+      if (usedPercent == null) usedPercent = legacy.used
+      if (resetAfterSeconds == null) resetAfterSeconds = legacy.resetAfterSeconds
+    }
+  }
+
+  if (!resetAt) {
+    resetAt = resolveFromSeconds(typedSnapshot, resetAfterSeconds)
+  }
+
+  return applyExpiredRule({ usedPercent, resetAt }, now)
+}