diff --git a/Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBChapterLoader.swift b/Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBChapterLoader.swift
index fb50c18..687fd51 100644
--- a/Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBChapterLoader.swift
+++ b/Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBChapterLoader.swift
@@ -65,6 +65,10 @@ final class RDEPUBChapterLoader {
         completion: @escaping (Result<RDEPUBRuntimeChapter, Error>) -> Void
     ) {
         if let cached = store.chapterData(for: spineIndex) {
+            RDEPUBBackgroundTrace.log(
+                "ChapterLoad",
+                "memory HIT spine=\(spineIndex) pages=\(cached.pages.count) priority=\(priority)"
+            )
             if let context {
                 scheduleDeferredCFIMapBuildIfNeeded(
                     for: cached,
@@ -92,6 +96,10 @@ final class RDEPUBChapterLoader {
 
         switch registration {
         case .joined(let existingPriority, let effectivePriority):
+            RDEPUBBackgroundTrace.log(
+                "ChapterLoad",
+                "join pendingLoad spine=\(spineIndex) existing=\(existingPriority) effective=\(effectivePriority)"
+            )
             return
         case .created:
             break
@@ -120,6 +128,20 @@ final class RDEPUBChapterLoader {
             let diskPageRanges = diskSummary?.pageRanges.map { $0.nsRange }
             let availablePageRanges = precomputedPageRanges ?? diskPageRanges
 
+            let pageRangeSource: String
+            if precomputedPageRanges != nil {
+                pageRangeSource = "HIT(memoryPageCount)"
+            } else if diskPageRanges != nil {
+                pageRangeSource = "HIT(diskSummary)"
+            } else {
+                pageRangeSource = "MISS(fullRender)"
+            }
+            RDEPUBBackgroundTrace.log(
+                "ChapterLoad",
+                "build start spine=\(spineIndex) priority=\(queuePriority) pageRanges=\(pageRangeSource)"
+            )
+            let buildStart = CFAbsoluteTimeGetCurrent()
+
             do {
 
                 let chapter = try self.buildChapter(
@@ -130,6 +152,10 @@ final class RDEPUBChapterLoader {
                     layoutSnapshot: layoutSnapshot
                 )
 
+                RDEPUBBackgroundTrace.log(
+                    "ChapterLoad",
+                    "build done spine=\(spineIndex) pages=\(chapter.pages.count) elapsedMs=\(Int((CFAbsoluteTimeGetCurrent() - buildStart) * 1000)) pageRanges=\(pageRangeSource)"
+                )
                 store.insertChapter(chapter)
                 let pc = RDEPUBRuntimePageCount(
                     cacheKey: cacheKey,
@@ -172,6 +198,10 @@ final class RDEPUBChapterLoader {
                     self.resolvePendingLoad(spineIndex: spineIndex, result: .success(chapter))
                 }
             } catch {
+                RDEPUBBackgroundTrace.log(
+                    "ChapterLoad",
+                    "build failed spine=\(spineIndex) pageRanges=\(pageRangeSource) error=\(String(describing: error))"
+                )
                 store.endPendingChapterLoad(for: spineIndex)
                 store.markBuilding(false)
                 self.resolvePendingLoad(spineIndex: spineIndex, result: .failure(error))