fix: eliminate auto-scroll jitter by deferring mark-as-read visual updates

ROOT CAUSE (confirmed by instrumentation):
Every markRead during auto-scroll mutated entries[idx].status,
causing SwiftUI to re-render the row (bold→regular, dot removed).
This changed card height, causing contentSize jumps of 10-128pt
per entry — visible as jitter.

FIX: During auto-scroll, collect entry IDs in deferredReadIDs
instead of mutating entries array. When auto-scroll stops,
flushDeferredReads() applies all status changes at once and
sends a single batched API call.

Manual scroll still marks immediately (no deferral needed since
the user controls the scroll position).

Removed all debug instrumentation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -94,19 +94,15 @@ 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 += count
+            offset += list.entries.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

@@ -13,6 +13,7 @@ struct EntryListView: View {
     @State private var cumulativeDown: CGFloat = 0
     @State private var cumulativeUp: CGFloat = 0
     @State private var markedByScroll: Set<Int> = []
+    @State private var deferredReadIDs: Set<Int> = []  // IDs to mark read when auto-scroll stops
 
     // Viewport height — use the first connected scene's screen.
     private var viewportHeight: CGFloat {
@@ -59,6 +60,11 @@ struct EntryListView: View {
                 // Stop auto-scroll on navigation return
                 isAutoScrolling = false
             }
+            .onChange(of: isAutoScrolling) { _, scrolling in
+                if !scrolling {
+                    flushDeferredReads()
+                }
+            }
             .refreshable {
                 await vm.refresh()
             }
@@ -112,22 +118,49 @@ 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"
-                            }
-
-                            Task {
-                                let api = ReaderAPI()
-                                try? await api.markEntries(ids: [entryId], status: "read")
-                                vm.counters = try? await api.getCounters()
+                            if isAutoScrolling {
+                                // Defer visual update — contentSize changes cause jitter
+                                // during auto-scroll. Collect IDs, apply when scroll stops.
+                                deferredReadIDs.insert(entryId)
+                            } else {
+                                // Manual scroll — apply immediately
+                                if let idx = vm.entries.firstIndex(where: { $0.id == entryId }) {
+                                    vm.entries[idx].status = "read"
+                                }
+                                Task {
+                                    let api = ReaderAPI()
+                                    try? await api.markEntries(ids: [entryId], status: "read")
+                                    vm.counters = try? await api.getCounters()
+                                }
                             }
                         }
                 }
             )
     }
 
+    // MARK: - Flush Deferred Reads
+
+    private func flushDeferredReads() {
+        guard !deferredReadIDs.isEmpty else { return }
+        let ids = Array(deferredReadIDs)
+        deferredReadIDs.removeAll()
+
+        // Apply all visual updates at once
+        for id in ids {
+            if let idx = vm.entries.firstIndex(where: { $0.id == id }) {
+                vm.entries[idx].status = "read"
+            }
+        }
+
+        // Single batched API call
+        Task {
+            let api = ReaderAPI()
+            try? await api.markEntries(ids: ids, status: "read")
+            vm.counters = try? await api.getCounters()
+        }
+    }
+
     // MARK: - Card Layout
 
     private var cardLayout: some View {

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

@@ -94,43 +94,20 @@ 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 }
 
-            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)
+            let delta = CGFloat(speed) * 60.0 * CGFloat(link.targetTimestamp - link.timestamp)
+            let newY = min(sv.contentOffset.y + delta, maxOffset)
 
             sv.contentOffset.y = newY
 
-            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)
 
             if newY >= maxOffset - 1 {