Stop zoom slider flicker during drag

Dragging the Settings zoom slider was applying app-wide zoom on every range change. That resized the Settings panel and the range control under the pointer, creating visible flicker and a poor drag feel.

The slider now keeps drag movement local to the Settings preview and commits the shared app zoom only when the drag is released or when keyboard/non-pointer changes occur. The control step is also reduced to one percent so adjustments feel less coarse.

Constraint: App-wide zoom changes resize the control currently being dragged
Rejected: Throttle live app zoom during drag | still resizes the target under the pointer and can flicker on slower WebViews
Confidence: high
Scope-risk: narrow
Directive: Do not apply app-wide zoom continuously during pointer drag; keep live resizing to keyboard shortcuts and final slider commit
Tested: bun run check:desktop
Tested: agent-browser Settings smoke confirms drag preview keeps cssZoom at 1 until release, then commits 1.23

desktop/src/__tests__/generalSettings.test.tsx

@@ -268,7 +268,7 @@ describe('Settings > General tab', () => {
     expect((uiZoomHeading.compareDocumentPosition(webFetchHeading) & Node.DOCUMENT_POSITION_FOLLOWING) !== 0).toBe(true)
   })
 
-  it('applies UI zoom while dragging so the slider and app zoom stay synchronized', async () => {
+  it('previews UI zoom while dragging and applies it once on release', async () => {
     render(<Settings />)
 
     fireEvent.click(screen.getByText('General'))
@@ -278,6 +278,7 @@ describe('Settings > General tab', () => {
     expect(screen.getByText('0 resets zoom to 100%.')).toBeInTheDocument()
 
     const slider = screen.getByLabelText('UI Zoom')
+    expect(slider).toHaveAttribute('step', '0.01')
 
     fireEvent.pointerDown(slider, { pointerId: 1 })
     await act(async () => {
@@ -287,8 +288,8 @@ describe('Settings > General tab', () => {
     })
 
     expect(screen.getAllByText('125%')).toHaveLength(2)
-    expect(useSettingsStore.getState().setUiZoom).toHaveBeenCalledWith(1.25)
-    expect(useSettingsStore.getState().uiZoom).toBe(1.25)
+    expect(useSettingsStore.getState().setUiZoom).not.toHaveBeenCalledWith(1.25)
+    expect(useSettingsStore.getState().uiZoom).toBe(1)
     expect(slider).toHaveValue('1.25')
     expect(slider).toHaveClass('settings-zoom-range')
     expect(slider.closest('.settings-zoom-control')).toHaveClass('is-dragging')

desktop/src/lib/appZoom.ts

@@ -4,7 +4,7 @@ export const DEFAULT_APP_ZOOM = 1
 export const MIN_APP_ZOOM = 0.5
 export const MAX_APP_ZOOM = 2
 export const APP_ZOOM_STEP = 0.1
-export const APP_ZOOM_CONTROL_STEP = 0.05
+export const APP_ZOOM_CONTROL_STEP = 0.01
 
 export type AppZoomAction = 'in' | 'out' | 'reset'
 

desktop/src/pages/Settings.tsx

@@ -1394,6 +1394,7 @@ function GeneralSettings() {
   const [notificationActionRunning, setNotificationActionRunning] = useState(false)
   const [uiZoomDraft, setUiZoomDraft] = useState(uiZoom)
   const [isUiZoomDragging, setIsUiZoomDragging] = useState(false)
+  const isUiZoomDraggingRef = useRef(false)
   const webSearchDirty = JSON.stringify(webSearchDraft) !== JSON.stringify(webSearch)
   const uiZoomPercent = Math.round(uiZoomDraft * 100)
   const uiZoomRangeProgress = `${Math.round(((uiZoomDraft - UI_ZOOM_MIN) / (UI_ZOOM_MAX - UI_ZOOM_MIN)) * 1000) / 10}%`
@@ -1523,11 +1524,14 @@ function GeneralSettings() {
     }
   }
 
-  const commitUiZoom = (value: number, options: { keepDragging?: boolean } = {}) => {
+  const setUiZoomDraggingState = (dragging: boolean) => {
+    isUiZoomDraggingRef.current = dragging
+    setIsUiZoomDragging(dragging)
+  }
+
+  const commitUiZoom = (value: number) => {
     const nextZoom = Number.isFinite(value) ? value : UI_ZOOM_DEFAULT
-    if (!options.keepDragging) {
-      setIsUiZoomDragging(false)
-    }
+    setUiZoomDraggingState(false)
     setUiZoomDraft(nextZoom)
     setUiZoom(nextZoom)
   }
@@ -1602,16 +1606,27 @@ function GeneralSettings() {
             step={UI_ZOOM_STEP}
             value={uiZoomDraft}
             onPointerDown={() => {
-              setIsUiZoomDragging(true)
+              setUiZoomDraggingState(true)
+            }}
+            onPointerUp={(e) => commitUiZoom(e.currentTarget.valueAsNumber)}
+            onPointerCancel={() => {
+              setUiZoomDraggingState(false)
+              setUiZoomDraft(uiZoom)
+            }}
+            onChange={(e) => {
+              const nextZoom = Number.isFinite(e.currentTarget.valueAsNumber)
+                ? e.currentTarget.valueAsNumber
+                : UI_ZOOM_DEFAULT
+              setUiZoomDraft(nextZoom)
+              if (!isUiZoomDraggingRef.current) {
+                setUiZoom(nextZoom)
+              }
             }}
-            onPointerUp={() => setIsUiZoomDragging(false)}
-            onPointerCancel={() => setIsUiZoomDragging(false)}
-            onChange={(e) => commitUiZoom(e.currentTarget.valueAsNumber, { keepDragging: isUiZoomDragging })}
             onBlur={(e) => {
               if (uiZoomDraft !== uiZoom) {
                 commitUiZoom(e.currentTarget.valueAsNumber)
               } else {
-                setIsUiZoomDragging(false)
+                setUiZoomDraggingState(false)
               }
             }}
             className="settings-zoom-range w-full"