perf: avoid duplicate markdown render on full load

WebViewMarkdownView.loadContent() 之前对同一份 content 调用了两次
MarkdownHTMLService.render：一次在 buildFullHTML 内部装配页面壳，
一次仅为写入从未被读取的 currentHeadings。后者额外执行了 Markdown
预处理、Document 解析与 formatter 遍历，对功能无贡献。

新增 buildFullHTML(renderResult:...) 重载，只装配 HTML 页面壳，不再
调用 render；loadContent() 先渲染一次再把结果交给该重载。原
buildFullHTML(content:...) 签名保留给 PDF 等调用方，内部只渲染一次
后委托新重载，HTML 模板、属性转义、CSS/JS 顺序逐字不变。

同时删除从未被读取的 currentHeadings 与 lastLoadedURL 状态及其赋值。
新增 MarkdownHTMLServiceTests 覆盖新重载与旧便利入口的输出合同。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: davidhoo

Sources/MarkdownReader/Views/WebViewMarkdownView.swift

@@ -106,10 +106,8 @@ struct WebViewMarkdownView: View {
     @Binding var exportedPage: WebPage?
     @State private var scrollPosition = ScrollPosition(edge: .top)
     @State private var lastLoadedContent: String = ""
-    @State private var lastLoadedURL: URL?
     @State private var scrollSyncTimer: Timer?
     @State private var isConfigured = false
-    @State private var currentHeadings: [MarkdownHTMLService.HeadingInfo] = []
     @State private var pendingScrollToLine: Int?
     @State private var zoomLevel: CGFloat = 1.0
     /// 上次处理的 contentVersion，用于检测程序化内容更新（reload/load）
@@ -260,8 +258,9 @@ struct WebViewMarkdownView: View {
 
     private func loadContent() {
         let baseURL = fileURL?.deletingLastPathComponent()
+        let renderResult = MarkdownHTMLService.render(content, baseURL: baseURL)
         let html = MarkdownHTMLService.buildFullHTML(
-            content: content,
+            renderResult: renderResult,
             themeCSS: themeCSS,
             contentPadding: contentPadding,
             maxContentWidthFollowsWindow: maxContentWidthFollowsWindow,
@@ -271,15 +270,11 @@ struct WebViewMarkdownView: View {
             documentCopiedTitle: L10n.tr(.contentCopied, language: language)
         )
 
-        let renderResult = MarkdownHTMLService.render(content, baseURL: baseURL)
-        currentHeadings = renderResult.headings
-
         scrollPosition = ScrollPosition(edge: .top)
 
         let effectiveBaseURL = baseURL ?? URL(string: "about:blank")!
         _ = page.load(html: html, baseURL: effectiveBaseURL)
         lastLoadedContent = content
-        lastLoadedURL = fileURL
 
         // 页面加载后同步查找栏显隐（查找栏打开期间渲染按钮隐藏）。
         syncDocumentCopyButtonVisibility()
@@ -299,7 +294,6 @@ struct WebViewMarkdownView: View {
     private func updateContent(_ content: String) {
         let baseURL = fileURL?.deletingLastPathComponent()
         let renderResult = MarkdownHTMLService.render(content, baseURL: baseURL)
-        currentHeadings = renderResult.headings
 
         let escapedHTML = renderResult.html
             .replacingOccurrences(of: "\\", with: "\\\\")

Sources/MarkdownReaderKit/Services/MarkdownHTMLService.swift

@@ -48,8 +48,21 @@ public enum MarkdownHTMLService {
     }
 
     public static func buildFullHTML(content: String, themeCSS: String, contentPadding: CGFloat, maxContentWidthFollowsWindow: Bool = false, baseURL: URL?, isDark: Bool = true, documentCopyTitle: String = "", documentCopiedTitle: String = "") -> String {
-        let renderResult = render(content, baseURL: baseURL)
+        buildFullHTML(
+            renderResult: render(content, baseURL: baseURL),
+            themeCSS: themeCSS,
+            contentPadding: contentPadding,
+            maxContentWidthFollowsWindow: maxContentWidthFollowsWindow,
+            baseURL: baseURL,
+            isDark: isDark,
+            documentCopyTitle: documentCopyTitle,
+            documentCopiedTitle: documentCopiedTitle
+        )
+    }
 
+    /// 以已有 `RenderResult` 装配完整 HTML 页面壳。不接收原始 Markdown，也不再次调用
+    /// `render`，仅供调用方（如 WebView 完整加载）复用单次解析结果，避免重复 Markdown 预处理与解析。
+    public static func buildFullHTML(renderResult: RenderResult, themeCSS: String, contentPadding: CGFloat, maxContentWidthFollowsWindow: Bool = false, baseURL: URL?, isDark: Bool = true, documentCopyTitle: String = "", documentCopiedTitle: String = "") -> String {
         let baseURLAttr = baseURL != nil ? " data-base-url=\"\(baseURL!.path.addingXMLAttributeEscapes)\"" : ""
         let copyTitleAttr = " data-document-copy-title=\"\(documentCopyTitle.addingXMLAttributeEscapes)\""
         let copiedTitleAttr = " data-document-copied-title=\"\(documentCopiedTitle.addingXMLAttributeEscapes)\""

Tests/MarkdownReaderTests/MarkdownHTMLServiceTests.swift

@@ -0,0 +1,47 @@
+import MarkdownReaderKit
+import XCTest
+
+/// MarkdownHTMLService 页面壳装配单测：覆盖新增的 `buildFullHTML(renderResult:...)`
+/// 重载与原 `buildFullHTML(content:...)` 便利入口的输出合同。不创建 WebView，不联网。
+final class MarkdownHTMLServiceTests: XCTestCase {
+
+    // MARK: - 新重载：以 RenderResult 为输入装配页面壳
+
+    func testBuildFullHTMLFromRenderResultEmbedsRenderedBodyAndShell() {
+        let result = MarkdownHTMLService.render("# Single parse")
+
+        let html = MarkdownHTMLService.buildFullHTML(
+            renderResult: result,
+            themeCSS: "--ink: #ffffff;",
+            contentPadding: 20,
+            baseURL: nil,
+            isDark: true,
+            documentCopyTitle: "Copy",
+            documentCopiedTitle: "Copied"
+        )
+
+        XCTAssertTrue(html.contains(result.html))
+        XCTAssertTrue(html.contains("id=\"mr-content\""))
+        XCTAssertTrue(html.contains("data-document-copy-title=\"Copy\""))
+        XCTAssertTrue(html.contains("data-is-dark=\"true\""))
+    }
+
+    // MARK: - 旧便利入口：签名与输出合同回归（PDF 等调用方未迁移）
+
+    func testBuildFullHTMLFromContentPreservesShellContract() {
+        let html = MarkdownHTMLService.buildFullHTML(
+            content: "# Heading",
+            themeCSS: "--ink: #000000;",
+            contentPadding: 16,
+            baseURL: nil,
+            isDark: false,
+            documentCopyTitle: "Copy",
+            documentCopiedTitle: "Copied"
+        )
+
+        XCTAssertTrue(html.contains("<h1 id=\"heading-1\""))
+        XCTAssertTrue(html.contains("id=\"mr-theme-style\""))
+        XCTAssertTrue(html.contains("mr:///js/markdown-reader.js"))
+        XCTAssertTrue(html.contains("id=\"mr-content\""))
+    }
+}