fix(web): inset sidebar scrollbar by 2px

apps/web/tests/sidebar-scrollbar.e2e.ts

@@ -106,7 +106,9 @@ interface ListMetrics {
   overflows: boolean
   /** Border-box width minus client width: the space the scrollbar takes out of the content area. */
   band: number
-  /** Distance from the first row background's right edge to the list border box. */
+  /** Distance from the scrollbar's right edge to the sidebar edge. */
+  scrollbarEdgeOffset: number
+  /** Distance from the first row background's right edge to the sidebar edge. */
   rowEdgeInset: number
   /** Client-area right edge in viewport coordinates (`clientWidth` excludes the scrollbar band). */
   clientRight: number
@@ -172,6 +174,8 @@ function measureList(page: Page): Promise<ListMetrics> {
     const pseudoWidth = getComputedStyle(list, '::-webkit-scrollbar').width
     const barWidth = pseudoWidth === 'auto' ? 15 : Number.parseFloat(pseudoWidth)
     const listRect = list.getBoundingClientRect()
+    const sidebarEdge = list.parentElement?.getBoundingClientRect().right
+    if (sidebarEdge === undefined) throw new Error('sidebar session list has no layout parent')
     return {
       gutter: style.scrollbarGutter,
       width: pseudoWidth,
@@ -183,7 +187,8 @@ function measureList(page: Page): Promise<ListMetrics> {
       hoverToken: resolve('--dsh-scrollbar-thumb-hover'),
       overflows: list.scrollHeight > list.clientHeight,
       band: listRect.width - list.clientWidth,
-      rowEdgeInset: listRect.right - row.getBoundingClientRect().right,
+      scrollbarEdgeOffset: sidebarEdge - listRect.right,
+      rowEdgeInset: sidebarEdge - row.getBoundingClientRect().right,
       clientRight: listRect.left + list.clientWidth,
       borderRight: listRect.right,
       timeRight: time.getBoundingClientRect().right,
@@ -211,9 +216,11 @@ function measureRowInset(page: Page): Promise<Pick<ListMetrics, 'overflows' | 'r
     if (list === null) throw new Error('sidebar session list not in the DOM')
     const row = list.querySelector<HTMLElement>('[role="treeitem"]')
     if (row === null) throw new Error('no row in the sidebar list')
+    const sidebarEdge = list.parentElement?.getBoundingClientRect().right
+    if (sidebarEdge === undefined) throw new Error('sidebar session list has no layout parent')
     return {
       overflows: list.scrollHeight > list.clientHeight,
-      rowEdgeInset: list.getBoundingClientRect().right - row.getBoundingClientRect().right,
+      rowEdgeInset: sidebarEdge - row.getBoundingClientRect().right,
     }
   })
 }
@@ -247,6 +254,7 @@ function renderGeometry(light: ListMetrics, dark: ListMetrics): string {
     `- --dsh-scrollbar-thumb-hover: ${metrics.hoverToken}`,
     `- list overflows: ${String(metrics.overflows)}`,
     `- reserved band: ${String(metrics.band)}px`,
+    `- scrollbar inset from the sidebar edge: ${String(metrics.scrollbarEdgeOffset)}px`,
     `- row background inset from the sidebar edge: ${String(metrics.rowEdgeInset)}px`,
     `- relative time covered by the bar: ${String(metrics.timeCoveredBy)}px`,
     `- relative time ends inside the content area: ${String(metrics.timeRight <= metrics.clientRight)}`,
@@ -325,6 +333,7 @@ describe('web e2e: sidebar session list scrollbar (reserved gutter / themed thum
     // drawn over it. Removing the declaration makes it exactly 0. The value
     // itself is not pinned — it tracks `scrollbar-width` and the platform.
     expect(metrics.band).toBeGreaterThan(0)
+    expect(metrics.scrollbarEdgeOffset).toBe(2)
     expect(metrics.rowEdgeInset).toBe(12)
     // The reported symptom, stated directly: no part of the row's relative time
     // lies under the bar. Measures 7 on clean master — the `h` of `1h` is the

apps/web/tests/snapshots/sidebar-scrollbar/geometry.expected.md

@@ -12,6 +12,7 @@
 - --dsh-scrollbar-thumb-hover: rgb(212, 212, 212)
 - list overflows: true
 - reserved band: 8px
+- scrollbar inset from the sidebar edge: 2px
 - row background inset from the sidebar edge: 12px
 - relative time covered by the bar: 0px
 - relative time ends inside the content area: true
@@ -29,6 +30,7 @@
 - --dsh-scrollbar-thumb-hover: rgb(84, 85, 87)
 - list overflows: true
 - reserved band: 8px
+- scrollbar inset from the sidebar edge: 2px
 - row background inset from the sidebar edge: 12px
 - relative time covered by the bar: 0px
 - relative time ends inside the content area: true

packages/client/ui-workspace/src/client/WorkspaceBrowser.module.css

@@ -6,6 +6,7 @@
 .root {
   --dsh-session-list-edge-inset: var(--dsh-sidebar-inline-padding);
   --dsh-session-list-scrollbar-width: 8px;
+  --dsh-session-list-scrollbar-offset: 2px;
   flex: 1;
   min-height: 0;
   display: flex;
@@ -214,13 +215,19 @@
 }
 
 /* List: the only scrolling region. Block children keep their design heights
-   under content overflow. The stable 8px themed scrollbar and the remaining
+   under content overflow. The 2px edge offset, stable 8px themed scrollbar,
-   padding together equal the shell's right inset, with or without overflow. */
+   and remaining padding equal the shell's right inset, with or without
+   overflow, so moving the bar does not move the rows. */
 .list {
   flex: 1;
   min-height: 0;
   overflow-y: auto;
-  padding-right: calc(var(--dsh-session-list-edge-inset) - var(--dsh-session-list-scrollbar-width));
+  margin-right: var(--dsh-session-list-scrollbar-offset);
+  padding-right: calc(
+    var(--dsh-session-list-edge-inset)
+    - var(--dsh-session-list-scrollbar-width)
+    - var(--dsh-session-list-scrollbar-offset)
+  );
   padding-bottom: 12px;
   scrollbar-gutter: stable;
 }

packages/client/ui-workspace/tests/browser-styles.spec.ts

@@ -43,12 +43,18 @@ describe('WorkspaceBrowser.module.css list', () => {
   it('counts the themed scrollbar inside the shell trailing inset', () => {
     expect(root?.get('--dsh-session-list-edge-inset')).toBe('var(--dsh-sidebar-inline-padding)')
     expect(root?.get('--dsh-session-list-scrollbar-width')).toBe('8px')
+    expect(root?.get('--dsh-session-list-scrollbar-offset')).toBe('2px')
     expect(root?.get('padding-right')).toBe('var(--dsh-session-list-edge-inset)')
     expect(listArea?.get('margin-right')).toBe('calc(-1 * var(--dsh-session-list-edge-inset))')
     expect(declarations('.fade')?.get('right')).toBe('var(--dsh-session-list-edge-inset)')
-    expect(list?.get('padding-right')).toBe(
+    expect(list?.get('margin-right')).toBe('var(--dsh-session-list-scrollbar-offset)')
-      'calc(var(--dsh-session-list-edge-inset) - var(--dsh-session-list-scrollbar-width))',
+    expect(list?.get('padding-right')).toBe([
-    )
+      'calc(',
+      'var(--dsh-session-list-edge-inset)',
+      '- var(--dsh-session-list-scrollbar-width)',
+      '- var(--dsh-session-list-scrollbar-offset)',
+      ')',
+    ].join(' '))
     expect(declarations('.list::-webkit-scrollbar')).toBeUndefined()
   })