feat: 实现大书远距目录跳转与后台补全优化方案

Phase 1: 稳定性优先
- 新增 RDEPUBJumpSession 保护机制，防止远距跳转后翻页串章
- 升级页图接管条件，增加 JumpSession 保护区检查
- 窗口扩展改为基于当前权威窗口方向

Phase 2: 补全优先级重排
- 新增 RDEPUBBackgroundPriorityPolicy 策略配置
- 实现 hot/warm/cold zone 优先级排序
- 添加失败重试机制（指数退避，最多3次）

Phase 3: 分段覆盖与最终收敛
- 新增 RDEPUBBackgroundCoverageStore 分段存储
- 新增 RDEPUBPageMapReconciliationCoordinator 页图接管仲裁
- 实现 LRU 淘汰和内存警告处理

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBReaderLocationCoordinator.swift

@@ -10,6 +10,9 @@ import Foundation
 final class RDEPUBReaderLocationCoordinator {
     private unowned let context: RDEPUBReaderContext
 
+    /// 上次翻页时的 spineIndex，用于检测跨章翻页
+    private var lastPageChangeSpineIndex: Int?
+
     init(context: RDEPUBReaderContext) {
         self.context = context
     }
@@ -23,6 +26,9 @@ final class RDEPUBReaderLocationCoordinator {
     ) -> Bool {
         guard let controller = context.controller,
               let readerView = context.readerView else { return false }
+        if context.bookPageMap != nil {
+            _ = context.runtime?.ensureOnDemandNavigationTargetAvailable(for: location)
+        }
         guard let targetPageNumber = controller.pageNumber(for: location) else {
             readerView.transitionToPage(pageNum: 0)
             context.readingSession?.transition(to: .idle)
@@ -50,6 +56,10 @@ final class RDEPUBReaderLocationCoordinator {
             context.readingSession?.transition(to: .jumping)
         }
         readerView.transitionToPage(pageNum: max(targetPageNumber - 1, 0), animated: animated)
+
+        // 记录翻页到 JumpSession
+        recordPageChangeIfNeeded()
+
         return true
     }
 
@@ -95,4 +105,40 @@ final class RDEPUBReaderLocationCoordinator {
         controller.delegate?.epubReader(controller, didUpdateCurrentTableOfContentsItem: controller.currentTableOfContentsItem)
         controller.updateReaderChrome()
     }
+
+    /// 记录翻页到 JumpSession
+    func recordPageChangeIfNeeded() {
+        guard let runtime = context.runtime,
+              let bookPageMap = context.bookPageMap,
+              let readerView = context.readerView else { return }
+
+        let currentPageNumber = readerView.currentPage + 1
+        guard let currentSpineIndex = bookPageMap.spineIndex(forAbsolutePage: currentPageNumber - 1) else {
+            return
+        }
+
+        if let lastSpineIndex = lastPageChangeSpineIndex,
+           lastSpineIndex != currentSpineIndex {
+            runtime.jumpSessionManager.recordPageChange(
+                fromSpineIndex: lastSpineIndex,
+                toSpineIndex: currentSpineIndex
+            )
+        }
+
+        lastPageChangeSpineIndex = currentSpineIndex
+
+        // 检查是否应该结束 JumpSession
+        let isIdle = context.secondsSinceLastUserNavigation() > 2.0
+        if let endReason = runtime.jumpSessionManager.checkSessionEnd(
+            currentSpineIndex: currentSpineIndex,
+            isIdle: isIdle
+        ) {
+            runtime.jumpSessionManager.endSession(endReason)
+        }
+    }
+
+    /// 重置翻页状态（用于重新加载等场景）
+    func resetPageChangeState() {
+        lastPageChangeSpineIndex = nil
+    }
 }