feat(header): Alt+W closes the active session tab, customizable in Settings

The close-with-neighbour-activation logic moved into a shared helper
(the strip and the shortcut use the same path). Alt+W is the default
because the browser owns Cmd/Ctrl+W on web; desktop users can rebind it
— the action is registered as customizable, so it appears in the
Settings shortcuts section and the shortcuts help automatically. VS
Code is excluded (it has no session tabs).

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

@@ -31,6 +31,7 @@ import { Icon } from '@/components/icon/Icon';
 import { cn } from '@/lib/utils';
 import { useI18n } from '@/lib/i18n';
 import { useSessionTabsStore } from '@/stores/useSessionTabsStore';
+import { closeSessionTabAndActivateNeighbour } from '@/lib/sessionTabs';
 import { useGlobalSessionsStore, resolveGlobalSessionDirectory } from '@/stores/useGlobalSessionsStore';
 import { useSessionUIStore } from '@/sync/session-ui-store';
 import { useGlobalSessionStatus } from '@/sync/sync-context';
@@ -391,13 +392,11 @@ export const SessionTabsStrip: React.FC<{
   const { t } = useI18n();
   const tabIds = useSessionTabsStore((state) => state.tabIds);
   const ensureTab = useSessionTabsStore((state) => state.ensureTab);
-  const closeTab = useSessionTabsStore((state) => state.closeTab);
   const closeOtherTabs = useSessionTabsStore((state) => state.closeOtherTabs);
   const reorderTabs = useSessionTabsStore((state) => state.reorderTabs);
 
   const currentSessionId = useSessionUIStore((state) => state.currentSessionId);
   const setCurrentSession = useSessionUIStore((state) => state.setCurrentSession);
-  const openNewSessionDraft = useSessionUIStore((state) => state.openNewSessionDraft);
   const activeSessions = useGlobalSessionsStore((state) => state.activeSessions);
 
   // Opening a session anywhere (sidebar, palette, deep link) adds its tab.
@@ -425,20 +424,9 @@ export const SessionTabsStrip: React.FC<{
     setCurrentSession(tab.id, resolveGlobalSessionDirectory(tab.session));
   }, [setCurrentSession]);
 
-  const activateNeighbour = React.useCallback((closedId: string) => {
-    const index = tabs.findIndex((tab) => tab.id === closedId);
-    const neighbour = tabs[index + 1] ?? tabs[index - 1] ?? null;
-    if (neighbour) {
-      handleSelect(neighbour);
-    } else {
-      openNewSessionDraft();
-    }
-  }, [tabs, handleSelect, openNewSessionDraft]);
-
   const handleClose = React.useCallback((id: string) => {
-    if (id === currentSessionId) activateNeighbour(id);
-    closeTab(id);
-  }, [activateNeighbour, closeTab, currentSessionId]);
+    closeSessionTabAndActivateNeighbour(id);
+  }, []);
 
   const handleCloseOthers = React.useCallback((id: string) => {
     closeOtherTabs(id);

packages/ui/src/hooks/useKeyboardShortcuts.ts

@@ -1,6 +1,7 @@
 import React from 'react';
 import { isTerminalEventTarget } from '@/lib/terminalFocus';
 import { useSessionUIStore } from '@/sync/session-ui-store';
+import { closeSessionTabAndActivateNeighbour } from '@/lib/sessionTabs';
 import { useSelectionStore } from '@/sync/selection-store';
 import * as sessionActions from '@/sync/session-actions';
 import { normalizeContextPanelDirectoryKey, useUIStore } from '@/stores/useUIStore';
@@ -299,6 +300,14 @@ export const useKeyboardShortcuts = () => {
         return;
       }
 
+      if (!isVSCodeRuntime() && eventMatchesShortcut(e, combo('close_session_tab'))) {
+        e.preventDefault();
+        if (currentSessionId) {
+          closeSessionTabAndActivateNeighbour(currentSessionId);
+        }
+        return;
+      }
+
       const matchedNewSessionShortcut = eventMatchesShortcut(e, combo('new_chat'));
       const matchedWorktreeShortcut = eventMatchesShortcut(e, combo('new_chat_worktree'));
 

packages/ui/src/lib/sessionTabs.ts

@@ -0,0 +1,33 @@
+import { useSessionTabsStore } from '@/stores/useSessionTabsStore';
+import { useGlobalSessionsStore, resolveGlobalSessionDirectory } from '@/stores/useGlobalSessionsStore';
+import { useSessionUIStore } from '@/sync/session-ui-store';
+
+/**
+ * Close one header session tab. Closing the active tab activates its right
+ * neighbour (falling back left), or opens a new-session draft when it was the
+ * last tab. Only tabs whose session is present in the loaded session list
+ * count as neighbours — the same rule the strip uses for rendering. The
+ * session itself is never touched.
+ */
+export const closeSessionTabAndActivateNeighbour = (sessionId: string): void => {
+  const { tabIds, closeTab } = useSessionTabsStore.getState();
+  if (!tabIds.includes(sessionId)) return;
+
+  const { currentSessionId, setCurrentSession, openNewSessionDraft } = useSessionUIStore.getState();
+  if (sessionId === currentSessionId) {
+    const sessionsById = new Map(
+      useGlobalSessionsStore.getState().activeSessions.map((session) => [session.id, session] as const),
+    );
+    const renderable = tabIds.filter((id) => sessionsById.has(id));
+    const index = renderable.indexOf(sessionId);
+    const neighbourId = renderable[index + 1] ?? renderable[index - 1] ?? null;
+    const neighbour = neighbourId ? sessionsById.get(neighbourId) : null;
+    if (neighbour) {
+      setCurrentSession(neighbour.id, resolveGlobalSessionDirectory(neighbour));
+    } else {
+      openNewSessionDraft();
+    }
+  }
+
+  closeTab(sessionId);
+};

packages/ui/src/lib/shortcuts.ts

@@ -239,6 +239,13 @@ const SHORTCUT_ACTIONS: ReadonlyArray<ShortcutAction> = [
     description: 'Create a new worktree and open a draft in it',
     customizable: true,
   },
+  {
+    id: 'close_session_tab',
+    defaultCombo: 'alt+w',
+    label: 'Close session tab',
+    description: 'Close the active session tab in the header (the session itself stays)',
+    customizable: true,
+  },
   {
     id: 'new_mini_chat',
     defaultCombo: 'mod+alt+n',