diff --git a/packages/ui/src/components/chat/MessageList.tsx b/packages/ui/src/components/chat/MessageList.tsx
index 8957f216..653f370d 100644
--- a/packages/ui/src/components/chat/MessageList.tsx
+++ b/packages/ui/src/components/chat/MessageList.tsx
@@ -19,25 +19,22 @@ import type { StreamPhase } from './message/types';
 import { useGlobalSessionsStore } from '@/stores/useGlobalSessionsStore';
 import { useSessionParts } from '@/sync/sync-context';
 import type { ReviewTransferDirection } from '@/lib/reviewFlow';
+import { isMobileSurfaceRuntime } from '@/lib/runtimeSurface';
 
 const MESSAGE_LIST_VIRTUALIZE_THRESHOLD = 5;
 const EMPTY_STATIC_ENTRY_MESSAGES: ChatMessageEntry[] = [];
 const EMPTY_UNGROUPED_MESSAGE_IDS = new Set<string>();
 const MESSAGE_LIST_BUFFER_SIZE = 900;
+// Touch surfaces fling-scroll natively and dispatch scroll events less often
+// than the virtualizer can repaint, so a desktop-sized buffer leaves blank gaps
+// during momentum that only fill once measurement catches up. A larger overscan
+// keeps more rows mounted around the viewport so fast flings stay populated.
+const MOBILE_MESSAGE_LIST_BUFFER_SIZE = 2400;
+const resolveMessageListBufferSize = (): number => (
+    isMobileSurfaceRuntime() ? MOBILE_MESSAGE_LIST_BUFFER_SIZE : MESSAGE_LIST_BUFFER_SIZE
+);
 const TIMELINE_CACHE_LIMIT = 16;
 
-const estimateHistoryEntryHeight = (entry: RenderEntry | undefined): number => {
-    if (!entry) {
-        return 160;
-    }
-
-    if (entry.kind === 'turn') {
-        return 180 + Math.min(entry.turn.assistantMessages.length, 4) * 100;
-    }
-
-    return 140;
-};
-
 const sameKeys = (a: readonly string[] | undefined, b: readonly string[] | undefined): boolean => {
     if (a === b) return true;
     if (!a || !b) return false;
@@ -982,8 +979,7 @@ const StaticHistoryList = React.memo(({ entries, shouldVirtualize, contentRef, s
             ref={virtualizerRef}
             data={entries}
             cache={virtualCache}
-            itemSize={virtualCache ? undefined : estimateHistoryEntryHeight(undefined)}
-            bufferSize={MESSAGE_LIST_BUFFER_SIZE}
+            bufferSize={resolveMessageListBufferSize()}
             shift={shift}
             scrollRef={scrollRef}
         >
diff --git a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
index a8e72106..13a0793c 100644
--- a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
+++ b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
@@ -60,6 +60,24 @@ export interface UseChatTimelineControllerResult {
 
 const TURN_MODEL_CACHE_MAX = 30
 const HISTORY_SCROLL_THRESHOLD = 200
+// On touch surfaces the user can drag continuously toward the top, and
+// loadEarlier is an async (network) fetch. A 200px lead is enough on desktop
+// (wheel + fast render) but the finger can outrun an in-flight fetch on mobile
+// and hit the very top before history lands. Give touch a much larger,
+// viewport-relative head start so the fetch completes before the top is
+// reached, regardless of how fast the user drags.
+const MOBILE_HISTORY_SCROLL_THRESHOLD_MIN = 1200
+const MOBILE_HISTORY_SCROLL_VIEWPORT_FACTOR = 2
+
+const resolveHistoryScrollThreshold = (clientHeight: number): number => {
+    if (!isMobileSurfaceRuntime()) {
+        return HISTORY_SCROLL_THRESHOLD
+    }
+    return Math.max(
+        MOBILE_HISTORY_SCROLL_THRESHOLD_MIN,
+        clientHeight * MOBILE_HISTORY_SCROLL_VIEWPORT_FACTOR,
+    )
+}
 const VSCODE_TURN_MODEL_CACHE_MAX = 4
 const VSCODE_TURN_MODEL_CACHE_MAX_MESSAGES = 30
 const MOBILE_TURN_MODEL_CACHE_MAX = 4
@@ -521,7 +539,7 @@ export const useChatTimelineController = ({
         const container = scrollRef.current;
         if (!container) return;
         if (isPinnedRef.current) return;
-        if (container.scrollTop >= HISTORY_SCROLL_THRESHOLD) return;
+        if (container.scrollTop >= resolveHistoryScrollThreshold(container.clientHeight)) return;
         if (!historySignalsRef.current.canLoadEarlier) return;
         if (isLoadingOlderRef.current || pendingRevealWorkRef.current) return;