根据提供的code differences信息，由于没有具体的代码变更内容，我将生成一个通用的commit message模板：

```
docs(readme): 更新文档说明

- 添加了项目使用指南
- 完善了API接口说明
- 修正了一些文字错误
```

注：由于未提供具体的代码差异信息，以上为示例格式。请提供具体的代码变更内容以便生成准确的commit message。

康康/Features/Trends/SeriesChartCard.swift

@@ -4,11 +4,23 @@ import Charts
 struct SeriesChartCard: View {
     let bucket: SeriesBucket
 
-    private var allPoints: [(line: SeriesBucket.SeriesLine, point: SeriesBucket.Point)] {
-        bucket.lines.flatMap { line in line.points.map { (line, $0) } }
+    // bucket 不可变,这些派生量在 init 里一次性算好存为 let,避免 body 内被
+    // header / chart / daysSpanLabel 多次访问时反复 flatMap / min / max 重算。
+    private let allPoints: [(line: SeriesBucket.SeriesLine, point: SeriesBucket.Point)]
+    private let dateDomain: ClosedRange<Date>?
+    private let valueDomain: ClosedRange<Double>?
+
+    init(bucket: SeriesBucket) {
+        self.bucket = bucket
+        let pts = bucket.lines.flatMap { line in line.points.map { (line, $0) } }
+        self.allPoints = pts
+        self.dateDomain = Self.makeDateDomain(pts)
+        self.valueDomain = Self.makeValueDomain(pts, lines: bucket.lines)
     }
 
-    private var dateDomain: ClosedRange<Date>? {
+    private static func makeDateDomain(
+        _ allPoints: [(line: SeriesBucket.SeriesLine, point: SeriesBucket.Point)]
+    ) -> ClosedRange<Date>? {
         let dates = allPoints.map(\.point.date)
         guard let lo = dates.min(), let hi = dates.max() else { return nil }
         if lo == hi {
@@ -21,14 +33,17 @@ struct SeriesChartCard: View {
         return lo...hi
     }
 
-    private var valueDomain: ClosedRange<Double>? {
+    private static func makeValueDomain(
+        _ allPoints: [(line: SeriesBucket.SeriesLine, point: SeriesBucket.Point)],
+        lines: [SeriesBucket.SeriesLine]
+    ) -> ClosedRange<Double>? {
         var lo = Double.greatestFiniteMagnitude
         var hi = -Double.greatestFiniteMagnitude
         for (_, p) in allPoints {
             lo = min(lo, p.value)
             hi = max(hi, p.value)
         }
-        for line in bucket.lines {
+        for line in lines {
             if let r = line.referenceRange {
                 lo = min(lo, r.lowerBound)
                 hi = max(hi, r.upperBound)