邻接窗口淘汰不再清除前瞻预取章节

scheduleAdjacentChapterPrefetches 的窗口外淘汰会把
maybePrefetchUpcomingChapters 刚预取的后续章节清掉,下一次
prepare 又触发重建,形成"淘汰-重建"循环。淘汰时保留当前章之后
lookahead 范围内的章节,lookahead 数量提为共享常量。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBChapterWarmupOrchestrator.swift

@@ -32,6 +32,8 @@ final class RDEPUBChapterWarmupOrchestrator {
 
     private let prepareRequestDebounceInterval: CFTimeInterval = 0.15
 
+    private static let upcomingChapterLookaheadCount = 2
+
     init(
         context: RDEPUBReaderContext,
         store: RDEPUBChapterRuntimeStore,
@@ -392,7 +394,10 @@ final class RDEPUBChapterWarmupOrchestrator {
             windowRadius: context.configuration.chapterWindowRadius
         )
 
-        for evictable in store.evictableSpineIndices() {
+        // Keep chapters that maybePrefetchUpcomingChapters is responsible for,
+        // otherwise the two policies evict/rebuild the same chapter in a loop.
+        let retainedLookaheadIndices = upcomingLookaheadSpineIndices(after: spineIndex)
+        for evictable in store.evictableSpineIndices() where !retainedLookaheadIndices.contains(evictable) {
             store.evict(spineIndex: evictable)
         }
 
@@ -410,11 +415,18 @@ final class RDEPUBChapterWarmupOrchestrator {
         }
     }
 
+    private func upcomingLookaheadSpineIndices(after spineIndex: Int) -> Set<Int> {
+        guard let publication = context.publication else { return [] }
+        let buildableIndices = buildableSpineIndices(in: publication)
+        guard let currentPosition = buildableIndices.firstIndex(of: spineIndex) else { return [] }
+        return Set(buildableIndices.dropFirst(currentPosition + 1).prefix(Self.upcomingChapterLookaheadCount))
+    }
+
     private func maybePrefetchUpcomingChapters(
         aroundAbsolutePageNumber pageNumber: Int,
         in bookPageMap: RDEPUBBookPageMap,
         threshold: Int = 3,
-        lookaheadChapterCount: Int = 2
+        lookaheadChapterCount: Int = RDEPUBChapterWarmupOrchestrator.upcomingChapterLookaheadCount
     ) {
         guard let publication = context.publication else { return }
         let absolutePageIndex = pageNumber - 1