diff --git a/ui-tui/src/app/useInputHandlers.ts b/ui-tui/src/app/useInputHandlers.ts
index fff73d9cfa..b18dcbbd16 100644
--- a/ui-tui/src/app/useInputHandlers.ts
+++ b/ui-tui/src/app/useInputHandlers.ts
@@ -296,7 +296,14 @@ export function useInputHandlers(ctx: InputHandlerContext): InputHandlerResult {
 
     if (key.pageUp || key.pageDown) {
       const viewport = terminal.scrollRef.current?.getViewportHeight() ?? Math.max(6, (terminal.stdout?.rows ?? 24) - 8)
-      const step = Math.max(4, viewport - 2)
+      // Half-viewport per keystroke.  A whole-viewport jump (our old
+      // `viewport - 2`) fully replaces what's on screen — no visual
+      // continuity, the user can't scan — AND it lands right at Ink's
+      // `delta < innerHeight` fast-path threshold, disqualifying the
+      // DECSTBM blit on every press.  Half-viewport keeps 50% continuity,
+      // well under the threshold, and two presses still scroll the same
+      // total distance.
+      const step = Math.max(4, Math.floor(viewport / 2))
 
       return scrollTranscript(key.pageUp ? -step : step)
     }
diff --git a/ui-tui/src/config/limits.ts b/ui-tui/src/config/limits.ts
index a2e817d862..889ac4d686 100644
--- a/ui-tui/src/config/limits.ts
+++ b/ui-tui/src/config/limits.ts
@@ -4,4 +4,20 @@ export const LIVE_RENDER_MAX_LINES = 240
 export const LONG_MSG = 300
 export const MAX_HISTORY = 800
 export const THINKING_COT_MAX = 160
-export const WHEEL_SCROLL_STEP = 6
+// Rows scrolled per wheel-notch event.
+//
+// One notch of a mechanical wheel emits multiple wheel events (3-5 per
+// click in most terminals; trackpad flicks emit 100+). Each event scrolls
+// WHEEL_SCROLL_STEP rows.  The product = rows-per-click.
+//
+// 1 = pure line-by-line.  Small per-event delta keeps Ink's DECSTBM fast
+// path firing (each scroll < viewport-1) and produces smooth visible
+// motion — the user can scan content mid-scroll.  We were at 6 before
+// (= ~20-30 rows per notch) which visually teleported and forced the
+// virtualization to reshape the mount range on every event.
+//
+// If this feels sluggish on precision scrolls, porting claude-code's
+// wheel accel state machine (ScrollKeybindingHandler.tsx) is the right
+// next step — it ramps step up during sustained fast clicks and decays
+// on pause.
+export const WHEEL_SCROLL_STEP = 1