style(header): session tabs follow the titlebar tab design language

Uniform compact tabs (h-7, 6px radius, 13px medium) that share the strip
width and shrink before scrolling, thin separators between inactive
neighbours that disappear around the active or hovered tab, a
hover-revealed menu button anchored to the tab's end, a soft selection
pill for the active tab, and hidden scrollbars with fade edges. The
active tab is single-line: the project/branch meta row stays only in the
VS Code header, which keeps the plain title.

packages/ui/src/components/layout/Header.tsx

@@ -1739,6 +1739,7 @@ export const Header: React.FC = () => {
                 <form
                   ref={headerRenameFormRef}
                   className="flex w-full min-w-0 items-center gap-2 leading-tight"
+                  onPointerDown={(event) => event.stopPropagation()}
                   onSubmit={(event) => {
                     event.preventDefault();
                     void saveHeaderSessionRename();
@@ -1755,7 +1756,7 @@ export const Header: React.FC = () => {
                       }
                     }}
                     placeholder={t('sessions.sidebar.session.menu.rename')}
-                    className="min-w-0 flex-1 bg-transparent typography-ui-label text-[14px] font-normal leading-tight outline-none placeholder:text-muted-foreground"
+                    className="min-w-0 flex-1 bg-transparent text-[13px] font-medium leading-4 outline-none placeholder:text-muted-foreground"
                   />
                   <button
                     type="submit"
@@ -1776,36 +1777,16 @@ export const Header: React.FC = () => {
                   </button>
                 </form>
               ) : (
-                <span className="truncate typography-ui-label text-[14px] font-normal leading-tight text-foreground max-w-full">
+                <span className="truncate text-[13px] font-medium leading-4 text-foreground max-w-full">
                   {isNewSessionDraftOpen ? t('sessions.switcher.draftTitle') : currentSessionTitle}
                 </span>
               )}
-              {showHeaderMetaRow ? (
-                <span className="flex min-w-0 max-w-full items-center gap-1.5 truncate typography-micro text-[10.5px] font-normal leading-tight text-muted-foreground/75">
-                  {activeProjectLabel ? <span className="truncate">{activeProjectLabel}</span> : null}
-                  {currentBranchLabel ? (
-                    <span className="inline-flex min-w-0 items-center gap-0.5">
-                      <Icon name="git-branch" className="h-3 w-3 flex-shrink-0 text-muted-foreground/70" />
-                      <span className="truncate">{currentBranchLabel}</span>
-                    </span>
-                  ) : null}
-                  {!isNewSessionDraftOpen && worktreeBadgeKind ? (
-                    <span className={cn(
-                      "inline-flex min-w-0 items-center gap-0.5",
-                      worktreeBadgeKind === 'attention' || worktreeBadgeKind === 'invalid' || worktreeBadgeKind === 'missing' ? 'text-status-warning' : 'text-muted-foreground/60'
-                    )}>
-                      <Icon name="alert" className="h-3 w-3 flex-shrink-0" />
-                      <span className="truncate">{worktreeBadge}</span>
-                    </span>
-                  ) : null}
-                </span>
-              ) : null}
             </div>
             <div className={cn(
               'flex h-[18px] shrink-0 items-center justify-center',
               // Top-aligned only when the title has a metadata line under it;
               // alone, the title is centred and the button must follow.
-              showHeaderMetaRow ? 'self-start' : 'self-center',
+              'self-center',
             )}>
               {currentSessionId && !isNewSessionDraftOpen && !isRenamingHeaderSession ? (
                 <DropdownMenu

packages/ui/src/components/layout/SessionTabsStrip.tsx

@@ -45,15 +45,16 @@ const ActiveTabShell: React.FC<{ id: string; children: React.ReactNode }> = ({ i
     <div
       ref={setNodeRef}
       style={{ transform: DndCSS.Translate.toString(transform), transition }}
-      className={cn('h-9 shrink-0 touch-none', isDragging && 'z-10 opacity-60')}
+      className={cn('session-tab-slot flex h-7 w-56 min-w-16 max-w-56 flex-shrink touch-none', isDragging && 'z-10 opacity-60')}
       data-active-session-tab
+      data-active="true"
       {...attributes}
       {...listeners}
     >
       <div
         role="tab"
         aria-selected
-        className="flex h-9 min-w-0 max-w-[340px] items-center rounded-[10px] bg-interactive-selection px-3"
+        className="flex h-7 w-full min-w-0 items-center rounded-md bg-interactive-selection px-2"
       >
         {children}
       </div>
@@ -85,7 +86,8 @@ const InactiveSessionTab: React.FC<{
     <div
       ref={setNodeRef}
       style={{ transform: DndCSS.Translate.toString(transform), transition }}
-      className={cn('h-8 shrink-0', isDragging && 'z-10 opacity-60')}
+      className={cn('session-tab-slot flex h-7 w-56 min-w-10 max-w-56 flex-shrink', isDragging && 'z-10 opacity-60')}
+      data-active="false"
       {...attributes}
       {...listeners}
     >
@@ -107,13 +109,19 @@ const InactiveSessionTab: React.FC<{
           }
         }}
         className={cn(
-          'group/session-tab flex h-8 max-w-[200px] cursor-pointer touch-none select-none items-center rounded-[10px] px-3',
-          'text-muted-foreground transition-colors duration-150 hover:bg-interactive-hover/40 hover:text-foreground',
-          menuOpen && 'bg-interactive-hover/40 text-foreground',
+          'group/session-tab relative flex h-7 w-full min-w-0 cursor-pointer touch-none select-none items-center rounded-md px-2',
+          'text-muted-foreground transition-colors duration-150 hover:bg-interactive-hover hover:text-foreground',
+          menuOpen && 'bg-interactive-hover text-foreground',
         )}
         title={title}
       >
-        <span className="min-w-0 truncate typography-ui-label text-[13px] font-normal leading-tight">
+        <span
+          className={cn(
+            'min-w-0 flex-1 truncate text-[13px] font-medium leading-4',
+            'group-hover/session-tab:pr-5',
+            menuOpen && 'pr-5',
+          )}
+        >
           {title}
         </span>
         <DropdownMenu open={menuOpen} onOpenChange={setMenuOpen}>
@@ -124,10 +132,10 @@ const InactiveSessionTab: React.FC<{
               onClick={(event) => event.stopPropagation()}
               onPointerDown={(event) => event.stopPropagation()}
               className={cn(
-                'ml-0 hidden w-0 shrink-0 items-center justify-center overflow-hidden rounded-md text-muted-foreground',
+                'absolute right-1 top-1/2 hidden size-5 -translate-y-1/2 items-center justify-center rounded text-muted-foreground',
                 'opacity-0 transition-opacity duration-150 hover:text-foreground',
-                'group-hover/session-tab:ml-1.5 group-hover/session-tab:flex group-hover/session-tab:h-5 group-hover/session-tab:w-5 group-hover/session-tab:opacity-100',
-                menuOpen && 'ml-1.5 flex h-5 w-5 opacity-100',
+                'group-hover/session-tab:flex group-hover/session-tab:opacity-100',
+                menuOpen && 'flex opacity-100',
               )}
             >
               <Icon name="more" className="size-4" />
@@ -298,7 +306,7 @@ export const SessionTabsStrip: React.FC<{ children: React.ReactNode }> = ({ chil
       <div
         ref={scrollRef}
         onScroll={updateEdges}
-        className="flex min-w-0 items-center gap-1 overflow-x-auto py-1 [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
+        className="flex min-w-0 flex-1 items-center gap-1.5 overflow-x-auto overscroll-x-contain [scrollbar-width:none] [-ms-overflow-style:none] [&::-webkit-scrollbar]:hidden"
         style={maskImage ? { maskImage, WebkitMaskImage: maskImage } : undefined}
       >
         <DndContext
@@ -315,7 +323,8 @@ export const SessionTabsStrip: React.FC<{ children: React.ReactNode }> = ({ chil
           <div
             role="tab"
             aria-selected
-            className="flex h-9 min-w-0 max-w-[340px] shrink-0 items-center rounded-[10px] bg-interactive-selection px-3"
+            className="session-tab-slot flex h-7 w-56 min-w-16 max-w-56 flex-shrink items-center rounded-md bg-interactive-selection px-2"
+            data-active="true"
           >
             {children}
           </div>

packages/ui/src/index.css

@@ -1781,3 +1781,25 @@ html.desktop-runtime [class*="cursor-pointer"] {
 html.desktop-runtime .markdown-content [data-openchamber-file-link="true"] {
   cursor: default;
 }
+
+/* Header session tabs: thin separators between inactive neighbours, hidden
+   around the active or hovered tab (mirrors the titlebar tab language). */
+.session-tab-slot {
+  position: relative;
+}
+.session-tab-slot:not(:first-child):not([data-active='true'])::before {
+  content: '';
+  position: absolute;
+  top: 8px;
+  inset-inline-start: -2.75px;
+  width: 1.5px;
+  height: 12px;
+  border-radius: 9999px;
+  background: var(--border);
+  opacity: 0.6;
+}
+.session-tab-slot[data-active='true'] + .session-tab-slot::before,
+.session-tab-slot:not([data-active='true']):hover::before,
+.session-tab-slot:not([data-active='true']):hover + .session-tab-slot::before {
+  display: none;
+}