fix(web): tighten sidebar session spacing

packages/client/ui-sidebar/src/client/SidebarRoot.module.css

@@ -196,9 +196,14 @@
   min-height: 0;
   display: flex;
   flex-direction: column;
+  margin-right: -12px;
   overflow: hidden;
 }
 
+.collapsed .regionArea {
+  margin-right: 0;
+}
+
 /* Foot seat: a pure layout socket pinned under the region; the ui-settings
    trigger row inside owns its own geometry (49px wide row / 36px rail
    circle) and hover chrome. */

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

@@ -8,6 +8,12 @@
   min-height: 0;
   display: flex;
   flex-direction: column;
+  box-sizing: border-box;
+  padding-right: 12px;
+}
+
+.root.rail {
+  padding-right: 0;
 }
 
 .iconButton {
@@ -167,9 +173,14 @@
   min-height: 0;
   display: flex;
   flex-direction: column;
+  margin-right: -12px;
   overflow: hidden;
 }
 
+.rail .listArea {
+  margin-right: 0;
+}
+
 /* Relative for the bottom fade overlay. */
 .treeBody {
   flex: 1;
@@ -202,27 +213,28 @@
 
 /* List: the only scrolling region. Block, not a flex column: as flex items
    the 54/34 rows would shrink under content overflow; block children keep
-   their design heights and the 4px rhythm rides margins instead of gap. */
+   their design heights do not shrink under content overflow. Its right
+   padding is the sole gap between row backgrounds and the sidebar edge; the
+   outer seats move their clip boundary out so they add no hidden inset. */
 .list {
+  --dsh-session-list-edge-inset: 12px;
+  --dsh-session-list-scrollbar-width: 8px;
   flex: 1;
   min-height: 0;
   overflow-y: auto;
+  padding-right: var(--dsh-session-list-edge-inset);
   padding-bottom: 12px;
-  /* Row trailing content (the relative time, and the hover action buttons
-     that replace it) sits flush against the row's 8px right padding, so an
-     overlaid scrollbar covers it. Reserving the gutter keeps the bar beside
-     the rows instead of on top of them; `stable` holds the reservation when
-     the list is short enough not to scroll, so expanding a group does not
-     shift every row left. */
   scrollbar-gutter: stable;
 }
 
-.list > [role='treeitem'] + [role='treeitem'] {
-  margin-top: 4px;
+.list::-webkit-scrollbar {
+  width: var(--dsh-session-list-scrollbar-width);
 }
 
-.searchTree > [role='treeitem'] + [role='treeitem'] {
-  margin-top: 4px;
+.list > [role='treeitem'] + [role='treeitem'],
+.searchTree > [role='treeitem'] + [role='treeitem'],
+.groupSection > * + * {
+  margin-top: 2px;
 }
 
 .searchStatus,
@@ -237,22 +249,11 @@
   color: var(--dsw-alias-label-secondary);
 }
 
-/* One workspace section: header row + expanded session run. Rows inside
-   keep the former flat-list 4px gap as sibling margins; the inter-group
-   breathing room (figma 133:7661 batch separator, 20px after an expanded
-   run) rides the NEXT section's top margin so the last group adds none. */
-.groupSection > * + * {
-  margin-top: 4px;
-}
-
+/* One workspace section: header row + a compact expanded session run. */
 .groupSection + .groupSection {
   margin-top: 4px;
 }
 
-.groupSection:has([aria-expanded='true']) + .groupSection {
-  margin-top: 20px;
-}
-
 .empty {
   padding: 16px 12px;
   color: var(--dsw-alias-label-tertiary);

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

@@ -1,8 +1,7 @@
 /**
  * WorkspaceBrowser scroll-region style contract, asserted against the CSS text
- * on disk: the session list reserves its scrollbar gutter so the scrollbar
- * cannot overlay row trailing content, and reserves it whether or not the list
- * currently overflows so expanding a group does not shift rows sideways.
+ * on disk: the session list keeps one stable right inset for row hover fills,
+ * with or without overflow, while outer clip seats add no hidden second inset.
  */
 import { readFileSync } from 'node:fs'
 import { fileURLToPath } from 'node:url'
@@ -32,17 +31,25 @@ function declarations(className: string): Map<string, string> | undefined {
 }
 
 describe('WorkspaceBrowser.module.css list', () => {
+  const root = declarations('root')
+  const listArea = declarations('listArea')
   const list = declarations('list')
+  const treeBody = declarations('treeBody')
 
   it('is the scrolling region', () => {
     expect(list).toBeDefined()
     expect(list!.get('overflow-y')).toBe('auto')
   })
 
-  it('reserves the scrollbar gutter unconditionally', () => {
-    // Row trailing content sits flush against the row's right padding, so an
-    // overlay scrollbar covers it. `stable` keeps the reservation when the list
-    // is short enough not to scroll, so expanding a group does not shift rows.
+  it('keeps row backgrounds edge-flush with the scrolling region', () => {
+    expect(root?.get('padding-right')).toBe('12px')
+    expect(listArea?.get('margin-right')).toBe('-12px')
+    expect(treeBody?.get('margin-right')).toBeUndefined()
+    expect(list?.get('margin-right')).toBeUndefined()
+    expect(list?.get('padding-right')).toBe('var(--dsh-session-list-edge-inset)')
+  })
+
+  it('reserves the scrollbar inside the stable visual inset', () => {
     expect(list!.get('scrollbar-gutter')).toBe('stable')
   })
 })