Remove temporary scroll-padding centering for boundary sidebar rows

Boundary reveals (first/last row) previously widened the virtual list
with paddingStart/paddingEnd to force centering, but nothing cleared
that padding once the reveal finished, leaving a phantom gap in the
sidebar (#8019 follow-up). Clamp boundary targets to the list edge via
revealElementInScrollContainer instead, and drop the now-unused
centering-padding helpers and state.

src/renderer/src/components/sidebar/WorktreeList.tsx

@@ -100,7 +100,6 @@ import {
   type RenderRow
 } from './worktree-list-virtual-rows'
 import {
-  getElementCenteringScrollPadding,
   revealElementInScrollContainer,
   WORKTREE_SIDEBAR_REVEAL_TOP_INSET
 } from './worktree-sidebar-reveal'
@@ -288,7 +287,6 @@ import {
 import { getFolderWorkspaceCardPrDisplay } from './folder-workspace-card-pr-display'
 
 export {
-  getCenteringScrollPadding,
   getScrollTopToRevealBounds,
   WORKTREE_SIDEBAR_REVEAL_TOP_INSET
 } from './worktree-sidebar-reveal'
@@ -1322,11 +1320,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
   const [worktreeDragState, setWorktreeDragState] = useState<WorktreeRowDragState>(
     WORKTREE_ROW_DRAG_INITIAL_STATE
   )
-  const [centeringScrollPadding, setCenteringScrollPadding] = useState<{
-    targetKey: string
-    start: number
-    end: number
-  } | null>(null)
   const [pendingRevealRetryTick, setPendingRevealRetryTick] = useState(0)
   const [documentVisibilityRevision, setDocumentVisibilityRevision] = useState(0)
   const [highlightedRevealRowKey, setHighlightedRevealRowKey] = useState<string | null>(null)
@@ -1976,8 +1969,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
     ),
     overscan: 10,
     gap: 6,
-    paddingStart: centeringScrollPadding?.start ?? 0,
-    paddingEnd: centeringScrollPadding?.end ?? 0,
     // Why: the active sticky group header is rendered inside the virtual list,
     // so TanStack's scroll math needs the same top inset as the exact DOM reveal.
     scrollPaddingStart: WORKTREE_SIDEBAR_REVEAL_TOP_INSET,
@@ -2129,30 +2120,10 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
           }
         }
         const optionId = getRenderRowOptionId(targetRow, pendingRevealWorktree.worktreeId)
-        const centeringTargetKey = `worktree:${optionId ?? pendingRevealWorktree.worktreeId}`
-        if (centeringScrollPadding && centeringScrollPadding.targetKey !== centeringTargetKey) {
-          setCenteringScrollPadding(null)
-          retryExactRevealOnNextFrame()
-          return
-        }
         const option = optionId
           ? document.getElementById(optionId)
           : getMountedWorktreeOptions(pendingRevealWorktree.worktreeId, container)[0]
         const mountedOption = container && option && container.contains(option) ? option : null
-        if (container && mountedOption) {
-          const additionalPadding = getElementCenteringScrollPadding(container, mountedOption)
-          if (additionalPadding && (additionalPadding.start > 0 || additionalPadding.end > 0)) {
-            // Why: the first and last virtual rows need temporary boundary space
-            // or the browser clamps their centered position to the list edge.
-            setCenteringScrollPadding({
-              targetKey: centeringTargetKey,
-              start: (centeringScrollPadding?.start ?? 0) + additionalPadding.start,
-              end: (centeringScrollPadding?.end ?? 0) + additionalPadding.end
-            })
-            retryExactRevealOnNextFrame()
-            return
-          }
-        }
         const revealedOption =
           container && mountedOption && revealElementInScrollContainer(container, mountedOption)
             ? mountedOption
@@ -2228,7 +2199,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
     pendingRevealRetryTick,
     flashRevealedRow,
     setRenamingWorktreeId,
-    centeringScrollPadding,
     schedulePendingRevealFrame,
     cancelPendingRevealFrames
   ])
@@ -2312,14 +2282,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
       }
 
       const container = scrollRef.current
-      // Why: only clear stale boundary padding here. While a worktree reveal is
-      // still pending, clearing would wipe the padding it just accumulated and
-      // its boundary target could exhaust retries without ever centering.
-      if (centeringScrollPadding && !pendingRevealWorktree) {
-        setCenteringScrollPadding(null)
-        retryExactRevealOnNextFrame()
-        return
-      }
       const revealedElement = container
         ? revealMountedSidebarRowElement(container, pendingRevealSidebarRow.rowKey)
         : null
@@ -2345,7 +2307,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
     }
   }, [
     pendingRevealSidebarRow,
-    pendingRevealWorktree,
     repoMap,
     projectGroups,
     projectGrouping,
@@ -2357,7 +2318,6 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
     pendingRevealRetryTick,
     flashRevealedRow,
     clearPendingRevealSidebarRow,
-    centeringScrollPadding,
     schedulePendingRevealFrame,
     cancelPendingRevealFrames
   ])

src/renderer/src/components/sidebar/worktree-list-scroll-adjustment.test.ts

@@ -1,12 +1,12 @@
 import { describe, expect, it, vi } from 'vitest'
 import {
   countRecordKeysByReference,
-  getCenteringScrollPadding,
   getScrollTopToRevealBounds,
   resolvePendingSidebarReveal,
   WORKTREE_SIDEBAR_REVEAL_TOP_INSET,
   shouldAdjustWorktreeSidebarMeasuredRowScroll
 } from './WorktreeList'
+import { revealElementInScrollContainer } from './worktree-sidebar-reveal'
 import {
   extractWorktreeVirtualRowIndexes,
   estimateRenderRowSize,
@@ -125,21 +125,6 @@ describe('shouldAdjustWorktreeSidebarMeasuredRowScroll', () => {
 })
 
 describe('getScrollTopToRevealBounds', () => {
-  it('requests leading space when the first target would be clamped above center', () => {
-    const container = makeScrollContainer(0, 400)
-
-    expect(
-      getCenteringScrollPadding(
-        container,
-        {
-          start: 34,
-          end: 74
-        },
-        WORKTREE_SIDEBAR_REVEAL_TOP_INSET
-      )
-    ).toEqual({ start: 163, end: 0 })
-  })
-
   it('centers a fully visible target', () => {
     const container = makeScrollContainer(100, 400)
 
@@ -170,19 +155,22 @@ describe('getScrollTopToRevealBounds', () => {
     ).toBe(136)
   })
 
-  it('requests trailing space when the last target would be clamped below center', () => {
-    const container = makeScrollContainer(100, 400, 500)
+  it('clamps a boundary target to the list edge instead of padding the list', () => {
+    // Regression (#8019 follow-up): centering first/last rows via temporary
+    // paddingStart/paddingEnd left a permanent phantom gap in the sidebar once
+    // the reveal finished, since nothing cleared the padding afterwards.
+    const container = {
+      scrollTop: 100,
+      clientHeight: 200,
+      contains: () => true,
+      getBoundingClientRect: () => ({ top: 0, bottom: 200 })
+    } as unknown as HTMLElement
+    const firstRow = {
+      getBoundingClientRect: () => ({ top: -40, bottom: 20 })
+    } as unknown as Element
 
-    expect(
-      getCenteringScrollPadding(
-        container,
-        {
-          start: 430,
-          end: 470
-        },
-        WORKTREE_SIDEBAR_REVEAL_TOP_INSET
-      )
-    ).toEqual({ start: 0, end: 133 })
+    expect(revealElementInScrollContainer(container, firstRow)).toBe(true)
+    expect(container.scrollTop).toBe(0)
   })
 })
 

src/renderer/src/components/sidebar/worktree-scroll-to-current-button.test.ts

@@ -9,8 +9,8 @@ describe('getScrollTopToRevealBounds', () => {
     }) as HTMLElement
 
   it('centers a mounted current workspace card that starts above the viewport', () => {
-    // Raw result may be negative; boundary reveals convert the deficit into
-    // temporary paddingStart instead of clamping (see getCenteringScrollPadding).
+    // Raw result may be negative; revealElementInScrollContainer clamps it to
+    // the list edge so boundary reveals never pad the list.
     expect(getScrollTopToRevealBounds(makeContainer(100, 200), { start: 60, end: 120 })).toBe(-10)
   })
 

src/renderer/src/components/sidebar/worktree-sidebar-reveal.ts

@@ -9,11 +9,6 @@ type SidebarRevealBounds = {
   end: number
 }
 
-type SidebarCenteringScrollPadding = {
-  start: number
-  end: number
-}
-
 function getElementScrollBounds(container: HTMLElement, element: Element): SidebarRevealBounds {
   const containerRect = container.getBoundingClientRect()
   const elementRect = element.getBoundingClientRect()
@@ -36,30 +31,6 @@ export function getScrollTopToRevealBounds(
   return targetCenter - viewportCenterOffset
 }
 
-export function getCenteringScrollPadding(
-  container: HTMLElement,
-  bounds: SidebarRevealBounds,
-  topInset = 0
-): SidebarCenteringScrollPadding {
-  const desiredScrollTop = getScrollTopToRevealBounds(container, bounds, topInset)
-  const maxScrollTop = Math.max(0, container.scrollHeight - container.clientHeight)
-  return {
-    start: Math.ceil(Math.max(0, -desiredScrollTop)),
-    end: Math.ceil(Math.max(0, desiredScrollTop - maxScrollTop))
-  }
-}
-
-export function getElementCenteringScrollPadding(
-  container: HTMLElement,
-  element: Element,
-  topInset = WORKTREE_SIDEBAR_REVEAL_TOP_INSET
-): SidebarCenteringScrollPadding | null {
-  if (!container.contains(element)) {
-    return null
-  }
-  return getCenteringScrollPadding(container, getElementScrollBounds(container, element), topInset)
-}
-
 export function revealElementInScrollContainer(container: HTMLElement, element: Element): boolean {
   if (!container.contains(element)) {
     return false
@@ -70,7 +41,8 @@ export function revealElementInScrollContainer(container: HTMLElement, element:
     WORKTREE_SIDEBAR_REVEAL_TOP_INSET
   )
   // Why: sidebar reveal is a focus handoff, so reposition immediately instead
-  // of making the user track an animated list.
+  // of making the user track an animated list. Boundary rows clamp to the list
+  // edge — padding the list so they can center leaves a phantom gap behind.
   container.scrollTop = Math.max(0, nextScrollTop)
   return true
 }