@@ -11,7 +11,7 @@
  */
 :root {
   --sidebar-width: 0px; /* 0 outside workspace; blocking script always sets actual value on workspace pages */
-  --sidebar-collapsed-width: 51px; /* icon rail on web; desktop overrides to 0 before first paint */
+  --sidebar-collapsed-width: 48px; /* icon rail on web; desktop overrides to 0 before first paint */
   --sidebar-expanded-width: 238px; /* SIDEBAR_WIDTH.DEFAULT; the width to restore to, held even while collapsed */
   --desktop-title-bar-height: 0px; /* macOS traffic-light lane; desktop overrides before first paint */
   --workspace-content-title-bar-inset: 0px; /* lane the content pane must leave clear; only non-zero when the pane, not the sidebar, sits under it */
 
@@ -75,7 +75,7 @@ export default function RootLayout({ children }: { children: React.ReactNode })
                 // The macOS desktop shell overlays native traffic lights on the
                 // workspace. Mark it before first paint so the sidebar reserves
                 // its inset title-bar lane without a post-hydration layout shift.
-                var collapsedSidebarWidth = 51;
+                var collapsedSidebarWidth = 48;
                 try {
                   if (window.simDesktop && /Mac/i.test(navigator.userAgent)) {
                     document.documentElement.setAttribute('data-sim-desktop-title-bar', 'inset');
 
@@ -7,13 +7,18 @@ export const RESOURCE_TAB_ICON_CLASS = 'size-[16px] text-[var(--text-icon)]'
 /** Shared geometry for the resource header and controls positioned over it. */
 export const RESOURCE_HEADER_CLASSES = {
   layout:
-    '[--resource-header-controls-height:43px] [--resource-header-end-inset:16px] [--resource-header-fixed-reserve:54px]',
+    '[--resource-header-controls-height:43px] [--resource-header-end-inset:16px] [--resource-header-fixed-reserve:54px] [--resource-header-toggle-size:30px]',
   bar: 'h-[calc(var(--resource-header-controls-height)_+_1px)]',
-  controls: 'h-[var(--resource-header-controls-height)]',
-  contentTop: 'top-[8.5px]',
+  overlay: 'absolute top-0 flex h-[var(--resource-header-controls-height)] items-center',
   startPadding: 'pl-[var(--resource-header-end-inset)]',
   endPadding: 'pr-[var(--resource-header-fixed-reserve)]',
   endPosition: 'right-[var(--resource-header-end-inset)]',
-  adjacentEndPosition: 'right-[var(--resource-header-fixed-reserve)]',
+  /**
+   * Sits a control 1px clear of the overlaid 30px collapse toggle — the same
+   * chip-to-chip gap the sidebar header cluster uses (`gap-[1px]`), so the
+   * credits chip and the toggle read as one cluster across both surfaces.
+   */
+  adjacentEndPosition:
+    'right-[calc(var(--resource-header-end-inset)_+_var(--resource-header-toggle-size)_+_1px)]',
   emptyAddOffset: '-translate-x-1.5',
 } as const
@@ -283,21 +283,32 @@ export function Home({ chatId, userName, userId, tableViewsEnabled }: HomeProps)
     setIsResourceCollapsed(true)
   }, [clearWidth])
 
+  const clearResourceActivity = useCallback((resourceId: string) => {
+    setResourceActivityIds((current) => {
+      if (!current.has(resourceId)) return current
+      const next = new Set(current)
+      next.delete(resourceId)
+      return next
+    })
+  }, [])
+
+  const expandResource = () => {
+    userOwnsResourceViewRef.current = true
+    const activeResourceId = activeResourceParamRef.current
+    if (activeResourceId) clearResourceActivity(activeResourceId)
+    setIsResourceCollapsed(false)
+  }
+
   const selectResourceFromUser = useCallback(
     (resourceId: string) => {
       userOwnsResourceViewRef.current = true
-      setResourceActivityIds((current) => {
-        if (!current.has(resourceId)) return current
-        const next = new Set(current)
-        next.delete(resourceId)
-        return next
-      })
+      clearResourceActivity(resourceId)
       if (effectiveActiveResourceIdRef.current === resourceId) return
       effectiveActiveResourceIdRef.current = resourceId
       activeResourceParamRef.current = resourceId
       setActiveResourceId(resourceId)
     },
-    [setActiveResourceId]
+    [setActiveResourceId, clearResourceActivity]
   )
 
   const addResourceFromUser = useCallback(
@@ -581,9 +592,17 @@ export function Home({ chatId, userName, userId, tableViewsEnabled }: HomeProps)
         {showEmptyState && (
           <div
             className={cn(
-              'absolute z-10',
-              RESOURCE_HEADER_CLASSES.contentTop,
-              RESOURCE_HEADER_CLASSES.adjacentEndPosition
+              'z-10',
+              RESOURCE_HEADER_CLASSES.overlay,
+              // Collapsed, the expand toggle overlays this corner, so the chip
+              // yields the fixed reserve; open, the toggle lives in the panel's
+              // corner and the chip takes the standard end inset itself.
+              isResourceCollapsed
+                ? RESOURCE_HEADER_CLASSES.adjacentEndPosition
+                : RESOURCE_HEADER_CLASSES.endPosition,
+              skipResourceTransition
+                ? 'transition-none'
+                : 'transition-[right] duration-200 [transition-timing-function:cubic-bezier(0.25,0.1,0.25,1)]'
             )}
           >
             <CreditsChip />
@@ -690,34 +709,14 @@ export function Home({ chatId, userName, userId, tableViewsEnabled }: HomeProps)
       </MothershipResourcesProvider>
 
       <div
-        className={cn(
-          'absolute top-0 z-30 flex items-center',
-          RESOURCE_HEADER_CLASSES.controls,
-          RESOURCE_HEADER_CLASSES.endPosition
-        )}
+        className={cn('z-30', RESOURCE_HEADER_CLASSES.overlay, RESOURCE_HEADER_CLASSES.endPosition)}
       >
         <Button
           variant='ghost'
           size={null}
           type='button'
-          onClick={
-            isResourceCollapsed
-              ? () => {
-                  userOwnsResourceViewRef.current = true
-                  const activeResourceId = activeResourceParamRef.current
-                  if (activeResourceId) {
-                    setResourceActivityIds((current) => {
-                      if (!current.has(activeResourceId)) return current
-                      const next = new Set(current)
-                      next.delete(activeResourceId)
-                      return next
-                    })
-                  }
-                  setIsResourceCollapsed(false)
-                }
-              : collapseResource
-          }
-          className='size-[30px] rounded-[8px] hover-hover:bg-[var(--surface-active)]'
+          onClick={isResourceCollapsed ? expandResource : collapseResource}
+          className='size-[var(--resource-header-toggle-size)] rounded-[8px] hover-hover:bg-[var(--surface-active)]'
           aria-label={isResourceCollapsed ? 'Expand resource view' : 'Collapse resource view'}
         >
           <span className='relative'>
 
@@ -16,6 +16,7 @@ import { File, Folder, MoreHorizontal, Pencil, Plus, SquareArrowUpRight } from '
 import Link from 'next/link'
 import type { WorkspaceFileRecord } from '@/lib/uploads/contexts/workspace'
 import { ConversationListItem } from '@/app/workspace/[workspaceId]/components'
+import { SIDEBAR_RAIL_CHIP_CLASS } from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
 import type { useHoverMenu } from '@/app/workspace/[workspaceId]/w/components/sidebar/hooks'
 import { interleaveSiblings } from '@/app/workspace/[workspaceId]/w/components/sidebar/utils'
 import type { WorkspaceFileFolderApi } from '@/hooks/queries/workspace-file-folders'
@@ -209,7 +210,7 @@ export function CollapsedSidebarMenu({
             <button
               type='button'
               aria-label={ariaLabel}
-              className={chipVariants({ fullWidth: true })}
+              className={cn(chipVariants({ fullWidth: true }), SIDEBAR_RAIL_CHIP_CLASS)}
             >
               {icon}
             </button>
 
@@ -31,6 +31,7 @@ import {
   SIDEBAR_DIVIDER_PAD_ABOVE_CLASS,
   SIDEBAR_DIVIDER_PAD_BELOW_CLASS,
   SIDEBAR_ITEM_GAP_CLASS,
+  SIDEBAR_RAIL_CHIP_CLASS,
   SIDEBAR_SECTION_GAP_CLASS,
 } from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
 import { SidebarTooltip } from '@/app/workspace/[workspaceId]/w/components/sidebar/sidebar'
@@ -305,7 +306,11 @@ export function SettingsSidebar({
         )}
       >
         <SidebarTooltip label='Back' enabled={showCollapsedTooltips}>
-          <button type='button' onClick={handleBack} className={chipVariants({ fullWidth: true })}>
+          <button
+            type='button'
+            onClick={handleBack}
+            className={cn(chipVariants({ fullWidth: true }), SIDEBAR_RAIL_CHIP_CLASS)}
+          >
             {/* The 16px slot every settings row gives its icon, so Back's label starts on their baseline. */}
             <span aria-hidden className={cn(chipIconSlotClass, 'text-[var(--text-icon)]')}>
               <ChevronLeft className='size-[14px]' />
@@ -352,7 +357,10 @@ export function SettingsSidebar({
                       (item.id === 'inbox'
                         ? !inboxEntitled
                         : !subscriptionAccess.hasUsableMaxAccess)
-                    const itemClassName = chipVariants({ active, fullWidth: true })
+                    const itemClassName = cn(
+                      chipVariants({ active, fullWidth: true }),
+                      SIDEBAR_RAIL_CHIP_CLASS
+                    )
                     const content = (
                       <>
                         <Icon className={chipContentIconClass} />
 
@@ -24,7 +24,10 @@ import { getDesktopUpdates } from '@/lib/desktop'
 import { getUserColor } from '@/lib/workspaces/colors'
 import { useWorkspaceHostContext } from '@/app/workspace/[workspaceId]/providers/workspace-host-provider'
 import type { SettingsSection } from '@/app/workspace/[workspaceId]/settings/navigation'
-import { SIDEBAR_ITEM_GAP_CLASS } from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
+import {
+  SIDEBAR_ITEM_GAP_CLASS,
+  SIDEBAR_RAIL_CHIP_CLASS,
+} from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
 import { SidebarTooltip } from '@/app/workspace/[workspaceId]/w/components/sidebar/sidebar'
 import { useUserProfile } from '@/hooks/queries/user-profile'
 import { useWorkspaceInvitePolicy } from '@/hooks/use-workspace-invite-policy'
@@ -237,11 +240,11 @@ export function SidebarFooter({
           <button
             type='button'
             data-item-id='profile'
-            className={
-              isCollapsed
-                ? cn(chipVariants({ fullWidth: true }), 'min-w-0')
-                : cn(chipVariants(), 'max-w-full')
-            }
+            className={cn(
+              chipVariants({ fullWidth: isCollapsed }),
+              isCollapsed ? 'min-w-0' : 'max-w-full',
+              SIDEBAR_RAIL_CHIP_CLASS
+            )}
           >
             {avatar}
             {profile ? (
@@ -293,7 +296,7 @@ export function SidebarFooter({
                than the rail, and a shrinking chip would be squeezed onto the avatar.
                Holding its size pushes it past the edge, where the aside's clip hides
                it until there is room. */
-            className='flex-shrink-0'
+            className={cn('flex-shrink-0', SIDEBAR_RAIL_CHIP_CLASS)}
           />
         </DropdownMenuTrigger>
       </SidebarTooltip>
 
@@ -30,6 +30,7 @@ import { DeleteModal } from '@/app/workspace/[workspaceId]/w/components/sidebar/
 import { CreateWorkspaceModal } from '@/app/workspace/[workspaceId]/w/components/sidebar/components/workspace-header/components/create-workspace-modal/create-workspace-modal'
 import { ViewInvitationsMenuItem } from '@/app/workspace/[workspaceId]/w/components/sidebar/components/workspace-header/components/pending-invitations/view-invitations-menu-item'
 import { ViewInvitationsModal } from '@/app/workspace/[workspaceId]/w/components/sidebar/components/workspace-header/components/pending-invitations/view-invitations-modal'
+import { SIDEBAR_RAIL_CHIP_CLASS } from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
 import { invitationKeys } from '@/hooks/queries/invitations'
 import {
   type Workspace,
@@ -442,7 +443,7 @@ function WorkspaceHeaderImpl({
           type='button'
           aria-label='Expand sidebar'
           onClick={onExpandSidebar}
-          className={chipVariants({ fullWidth: true })}
+          className={cn(chipVariants({ fullWidth: true }), SIDEBAR_RAIL_CHIP_CLASS)}
         >
           <div className='relative flex size-[16px] flex-shrink-0 items-center justify-center'>
             {activeWorkspaceFull?.logoUrl ? (
 
@@ -30,6 +30,34 @@ export const SIDEBAR_ITEM_GAP_CLASS = 'gap-[1px]'
 export const SIDEBAR_DIVIDER_PAD_ABOVE_CLASS = 'pb-2'
 export const SIDEBAR_DIVIDER_PAD_BELOW_CLASS = 'pt-2'
 
+/**
+ * Rail-chip geometry for the collapsed sidebar, gated by the `group/rail`
+ * marker on the sidebar `aside` (the hover-peek card drops `data-collapsed`,
+ * so peeked rows stay expanded). Collapses a full-width row to the natural
+ * icon-only chip — 32px, the chip's own `px-2` + 16px glyph, matching the
+ * header's Search/Collapse pills. Only the WIDTH is overridden: the rail is
+ * 48px precisely so that the plain 8px item gutter centers the chip
+ * ((48 − 32) / 2 = 8) and puts the glyph (24px in) on the rail's midline —
+ * the same 24px column the expanded rows use, so NOTHING moves on toggle.
+ * At the previous 51px rail those goals were mutually exclusive by 1.5px
+ * (rail midline 25.5 vs glyph column 24), which produced either a
+ * left-biased rail or a drift on toggle; keep the rail width and this chip
+ * width commensurate (rail = chip + 2 × gutter) if either ever changes.
+ * Collapsing, the width tweens down to 32px on the 175ms curve the rail
+ * closes on; expanding targets `auto` (not interpolable), so the chip snaps
+ * to the still-narrow rail's width and stretch-tracks it open. The duration
+ * is `!important` because the aside zeroes chip transition durations
+ * (`[&_.group.cursor-pointer]:duration-0`) for instant hover fills — colors
+ * are excluded from the property list here, so hover fills keep snapping.
+ */
+export const SIDEBAR_RAIL_CHIP_CLASS = [
+  'transition-[width]',
+  '![transition-duration:175ms]',
+  '[transition-timing-function:cubic-bezier(0.25,0.1,0.25,1)]',
+  'motion-reduce:!transition-none',
+  'group-data-[collapsed]/rail:w-[32px]',
+].join(' ')
+
 /**
  * Nested-selector variants for cmdk-based surfaces (e.g. the search modal).
  * Written as complete literal strings so Tailwind's JIT can detect them.
 
@@ -77,6 +77,7 @@ import {
   SIDEBAR_DIVIDER_PAD_ABOVE_CLASS,
   SIDEBAR_DIVIDER_PAD_BELOW_CLASS,
   SIDEBAR_ITEM_GAP_CLASS,
+  SIDEBAR_RAIL_CHIP_CLASS,
   SIDEBAR_SECTION_GAP_CLASS,
 } from '@/app/workspace/[workspaceId]/w/components/sidebar/constants'
 import {
@@ -355,6 +356,7 @@ const SidebarNavItem = memo(function SidebarNavItem({
       leftIcon={item.icon}
       active={active}
       fullWidth
+      className={SIDEBAR_RAIL_CHIP_CLASS}
       onClick={
         item.onClick
           ? (e) => {
@@ -374,6 +376,7 @@ const SidebarNavItem = memo(function SidebarNavItem({
       leftIcon={item.icon}
       active={active}
       fullWidth
+      className={SIDEBAR_RAIL_CHIP_CLASS}
       onClick={item.onClick}
     >
       {item.label}
@@ -1351,7 +1354,7 @@ export const Sidebar = memo(function Sidebar({
       />
       <div className='relative h-full'>
         <aside
-          className='sidebar-container relative h-full overflow-hidden bg-[var(--surface-1)] [&_.group.cursor-pointer]:duration-0'
+          className='group/rail sidebar-container relative h-full overflow-hidden bg-[var(--surface-1)] [&_.group.cursor-pointer]:duration-0'
           data-collapsed={isCollapsed || undefined}
           aria-label='Workspace sidebar'
           onClick={handleSidebarClick}
@@ -1404,11 +1407,24 @@ export const Sidebar = memo(function Sidebar({
                * between them. `gap-[1px]` rather than `gap-px`: the `px` spacing key
                * is remapped to `--border-width`, which thins to 0.5px on hidpi so
                * hairline rules stay hairlines.
+               *
+               * The expanded width is EXPLICIT (2 icon chips × 32px + the 1px gap;
+               * 32px when the desktop inset title bar hides the collapse chip), never
+               * `auto`: `w-0 → auto` cannot interpolate, so on expand the cluster
+               * snapped to full width while the rail was still 51px wide — and since
+               * the cluster refuses to flex-shrink (min-width: auto) while the
+               * workspace chip's wrapper is `min-w-0 flex-1`, the workspace chip
+               * crushed to zero and the hover-filled Search chip landed exactly under
+               * the cursor on the workspace icon: a visible flash on every expand.
+               * With both endpoints explicit, the width tweens in step with the rail
+               * and the workspace chip keeps its space throughout.
                */}
               <div
                 className={cn(
-                  'flex h-[30px] items-center gap-[1px] overflow-hidden transition-all duration-200',
-                  isCollapsed && 'w-0 opacity-0'
+                  'flex h-[30px] items-center gap-[1px] overflow-hidden transition-all duration-200 [transition-timing-function:cubic-bezier(0.25,0.1,0.25,1)]',
+                  isCollapsed
+                    ? 'w-0 opacity-0'
+                    : 'w-[65px] [[data-sim-desktop-title-bar=inset]_&]:w-[32px]'
                 )}
               >
                 <SidebarTooltip