debug: auto-scroll jitter instrumentation — tick timing, contentSize, loadMore, markRead

ios/Platform/Platform/Features/Reader/ViewModels/ReaderViewModel.swift

@@ -94,15 +94,19 @@ final class ReaderViewModel {
     func loadMore() async {
         guard !isLoadingMore, hasMore else { return }
         isLoadingMore = true
+        print("[SCROLL-DBG] 📥 loadMore START offset=\(offset)")
 
         do {
             let list = try await fetchEntries(offset: offset)
+            let count = list.entries.count
             entries.append(contentsOf: list.entries)
             total = list.total
-            offset += list.entries.count
+            offset += count
             hasMore = offset < list.total
+            print("[SCROLL-DBG] 📥 loadMore END appended=\(count) total=\(entries.count) hasMore=\(hasMore)")
         } catch {
             self.error = error.localizedDescription
+            print("[SCROLL-DBG] 📥 loadMore FAILED: \(error)")
         }
         isLoadingMore = false
     }

ios/Platform/Platform/Features/Reader/Views/EntryListView.swift

@@ -112,6 +112,7 @@ struct EntryListView: View {
                                   frame.maxY < 30 else { return }
 
                             markedByScroll.insert(entryId)
+                            print("[SCROLL-DBG] 📖 markRead id=\(entryId) entriesCount=\(vm.entries.count)")
 
                             if let idx = vm.entries.firstIndex(where: { $0.id == entryId }) {
                                 vm.entries[idx].status = "read"

ios/Platform/Platform/Features/Reader/Views/ScrollViewDriver.swift

@@ -94,25 +94,45 @@ struct ScrollViewDriver: UIViewRepresentable {
             displayLink = nil
         }
 
+        private var lastTickTime: CFAbsoluteTime = 0
+        private var lastContentSize: CGFloat = 0
+        private var tickCount = 0
+
         @objc private func tick(_ link: CADisplayLink) {
             guard let sv = scrollView else {
                 stopAndNotify()
                 return
             }
 
+            let now = CFAbsoluteTimeGetCurrent()
             let maxOffset = sv.contentSize.height - sv.bounds.height + sv.contentInset.bottom
             guard maxOffset > 0 else { return }
 
-            // 60pt/sec at 1.0x speed, scaled by actual frame duration
-            let delta = CGFloat(speed) * 60.0 * CGFloat(link.targetTimestamp - link.timestamp)
-            let newY = min(sv.contentOffset.y + delta, maxOffset)
+            let frameDuration = link.targetTimestamp - link.timestamp
+            let expectedDelta = CGFloat(speed) * 60.0 * CGFloat(frameDuration)
+            let beforeY = sv.contentOffset.y
+            let newY = min(beforeY + expectedDelta, maxOffset)
 
             sv.contentOffset.y = newY
 
-            // Notify delegate so tab bar minimize behavior triggers
+            let actualDelta = sv.contentOffset.y - beforeY
+
+            // Detect jitter: contentSize changed, or actual delta differs from expected
+            let contentSizeChanged = sv.contentSize.height != lastContentSize
+            let wallDelta = lastTickTime > 0 ? (now - lastTickTime) * 1000 : 0
+            let isJitter = contentSizeChanged || wallDelta > 25 // >25ms between frames = dropped frame
+
+            tickCount += 1
+            if isJitter || tickCount % 120 == 0 {
+                // Log on jitter or every 2 seconds
+                print("[SCROLL-DBG] \(isJitter ? "⚠️ JITTER" : "✅ ok") wallΔ=\(String(format:"%.1f", wallDelta))ms frameDur=\(String(format:"%.1f", frameDuration*1000))ms expΔ=\(String(format:"%.1f", expectedDelta))pt actΔ=\(String(format:"%.1f", actualDelta))pt y=\(Int(sv.contentOffset.y)) contentH=\(Int(sv.contentSize.height)) csChanged=\(contentSizeChanged) speed=\(String(format:"%.2f", speed))")
+            }
+
+            lastTickTime = now
+            lastContentSize = sv.contentSize.height
+
             originalDelegate?.scrollViewDidScroll?(sv)
 
-            // Stop at bottom
             if newY >= maxOffset - 1 {
                 stopAndNotify()
             }