refactor(desktop): tighten right-rail tab close API

Promote closeRightRailTab/closeActiveRightRailTab as the single
public entry point. Drops the activeTabRef + handleCloseDocument
indirection in ChatPreviewRail, the unused $rightRailHasContent
atom, and the legacy dismissFilePreviewTarget alias. -70 LOC.

apps/desktop/src/app/chat/right-rail/preview.tsx

@@ -1,5 +1,5 @@
 import { useStore } from '@nanostores/react'
-import { type MouseEvent, useCallback, useEffect, useMemo, useRef } from 'react'
+import { useEffect, useMemo } from 'react'
 
 import type { SetTitlebarToolGroup } from '@/app/shell/titlebar-controls'
 import { X } from '@/lib/icons'
@@ -14,9 +14,8 @@ import {
   $filePreviewTabs,
   $previewReloadRequest,
   $previewTarget,
-  closeFilePreviewTab,
-  dismissPreviewTarget,
-  type FilePreviewTab,
+  closeActiveRightRailTab,
+  closeRightRailTab,
   type PreviewTarget
 } from '@/store/preview'
 
@@ -39,21 +38,16 @@ interface ChatPreviewRailProps {
 }
 
 interface RailTab {
-  closeLabel: string
   id: RightRailTabId
   label: string
   target: PreviewTarget
 }
 
-function previewTabLabel(target: PreviewTarget): string {
+function tabLabelFor(target: PreviewTarget): string {
   const value = target.label || target.path || target.source || target.url
-  const parts = value.split(/[\\/]/).filter(Boolean)
+  const tail = value.split(/[\\/]/).filter(Boolean).at(-1)
 
-  return parts.at(-1) || value || 'Preview'
-}
-
-function tabLabel(tab: FilePreviewTab): string {
-  return previewTabLabel(tab.target)
+  return tail || value || 'Preview'
 }
 
 export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatPreviewRailProps) {
@@ -64,30 +58,13 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
 
   const tabs = useMemo<readonly RailTab[]>(
     () => [
-      ...(previewTarget
-        ? [
-            {
-              closeLabel: 'Close preview',
-              id: RIGHT_RAIL_PREVIEW_TAB_ID,
-              label: 'Preview',
-              target: previewTarget
-            } satisfies RailTab
-          ]
-        : []),
-      ...filePreviewTabs.map(tab => ({
-        closeLabel: `Close ${tabLabel(tab)}`,
-        id: tab.id,
-        label: tabLabel(tab),
-        target: tab.target
-      }))
+      ...(previewTarget ? [{ id: RIGHT_RAIL_PREVIEW_TAB_ID, label: 'Preview', target: previewTarget } as RailTab] : []),
+      ...filePreviewTabs.map(({ id, target }) => ({ id, label: tabLabelFor(target), target }) as RailTab)
     ],
     [filePreviewTabs, previewTarget]
   )
 
   const activeTab = tabs.find(tab => tab.id === activeTabId) ?? tabs[0]
-  // Read-by-ref so close handlers stay reference-stable across renders.
-  const activeTabRef = useRef<RailTab | undefined>(activeTab)
-  activeTabRef.current = activeTab
 
   useEffect(() => {
     if (activeTab && activeTab.id !== activeTabId) {
@@ -95,32 +72,6 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
     }
   }, [activeTab, activeTabId])
 
-  const closeRailTab = useCallback((tab: RailTab) => {
-    if (tab.id === RIGHT_RAIL_PREVIEW_TAB_ID) {
-      dismissPreviewTarget()
-
-      return
-    }
-
-    closeFilePreviewTab(tab.id)
-  }, [])
-
-  // Stable: PreviewPane lists onClose in a useEffect dep array that pushes
-  // titlebar tools. A fresh closure every render → setTitlebarToolGroup every
-  // render → DesktopController setState → re-render → ∞.
-  const handleCloseDocument = useCallback(() => {
-    const tab = activeTabRef.current
-
-    if (tab) {
-      closeRailTab(tab)
-    }
-  }, [closeRailTab])
-
-  const closeTab = (event: MouseEvent, tab: RailTab) => {
-    event.stopPropagation()
-    closeRailTab(tab)
-  }
-
   if (!activeTab) {
     return null
   }
@@ -158,13 +109,13 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
                 {tab.label}
               </button>
               <button
-                aria-label={tab.closeLabel}
+                aria-label={`Close ${tab.label}`}
                 className={cn(
                   'mr-1.5 hidden size-4 shrink-0 place-items-center rounded-sm text-muted-foreground/55 transition-colors hover:bg-accent hover:text-foreground focus-visible:grid group-hover/tab:grid',
                   active && 'grid'
                 )}
-                onClick={event => closeTab(event, tab)}
-                title={tab.closeLabel}
+                onClick={() => closeRightRailTab(tab.id)}
+                title={`Close ${tab.label}`}
                 type="button"
               >
                 <X className="size-3" />
@@ -177,7 +128,7 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
       <div className="min-h-0 flex-1 overflow-hidden">
         <PreviewPane
           embedded
-          onClose={handleCloseDocument}
+          onClose={closeActiveRightRailTab}
           onRestartServer={isPreview ? onRestartServer : undefined}
           reloadRequest={previewReloadRequest}
           setTitlebarToolGroup={setTitlebarToolGroup}

apps/desktop/src/app/desktop-controller.tsx

@@ -19,7 +19,7 @@ import {
   SIDEBAR_MAX_WIDTH,
   unpinSession
 } from '../store/layout'
-import { $filePreviewTarget, $previewTarget, dismissFilePreviewTarget, dismissPreviewTarget } from '../store/preview'
+import { $filePreviewTarget, $previewTarget, closeActiveRightRailTab } from '../store/preview'
 import {
   $activeSessionId,
   $currentCwd,
@@ -138,18 +138,6 @@ export function DesktopController() {
   }, [chatOpen, filePreviewTarget, previewTarget])
 
   useEffect(() => {
-    const closePreview = () => {
-      if ($filePreviewTarget.get()) {
-        dismissFilePreviewTarget()
-
-        return
-      }
-
-      if ($previewTarget.get()) {
-        dismissPreviewTarget()
-      }
-    }
-
     const onKeyDown = (event: KeyboardEvent) => {
       if (!$filePreviewTarget.get() && !$previewTarget.get()) {
         return
@@ -158,11 +146,11 @@ export function DesktopController() {
       if ((event.metaKey || event.ctrlKey) && !event.altKey && !event.shiftKey && event.key.toLowerCase() === 'w') {
         event.preventDefault()
         event.stopPropagation()
-        closePreview()
+        closeActiveRightRailTab()
       }
     }
 
-    const unsubscribe = window.hermesDesktop?.onClosePreviewRequested?.(closePreview)
+    const unsubscribe = window.hermesDesktop?.onClosePreviewRequested?.(closeActiveRightRailTab)
 
     window.addEventListener('keydown', onKeyDown, { capture: true })
 

apps/desktop/src/store/preview.test.ts

@@ -10,7 +10,7 @@ import {
   $sessionPreviewRegistry,
   beginPreviewServerRestart,
   clearSessionPreviewRegistry,
-  dismissFilePreviewTarget,
+  closeActiveRightRailTab,
   dismissPreviewTarget,
   getSessionPreviewRecord,
   type PreviewTarget,
@@ -114,7 +114,7 @@ describe('preview store', () => {
     expect($previewTarget.get()).toEqual(withRenderMode(preview, 'preview'))
     expect(getSessionPreviewRecord('session-1')?.normalized).toEqual(withRenderMode(preview, 'preview'))
 
-    dismissFilePreviewTarget()
+    closeActiveRightRailTab()
 
     expect($filePreviewTarget.get()).toBeNull()
     expect($previewTarget.get()).toEqual(withRenderMode(preview, 'preview'))

apps/desktop/src/store/preview.ts

@@ -58,9 +58,6 @@ export const $filePreviewTarget = computed([$filePreviewTabs, $rightRailActiveTa
 
   return tabs.find(tab => tab.id === activeTabId)?.target ?? null
 })
-export const $rightRailHasContent = computed([$previewTarget, $filePreviewTabs], (target, tabs) =>
-  Boolean(target || tabs.length)
-)
 export const $previewReloadRequest = atom(0)
 export const $previewServerRestart = atom<PreviewServerRestart | null>(null)
 export const $previewServerRestartStatus = computed($previewServerRestart, restart => restart?.status ?? 'idle')
@@ -368,7 +365,7 @@ export function dismissPreviewTarget() {
   }
 }
 
-export function closeFilePreviewTab(tabId: RightRailTabId) {
+function closeFilePreviewTab(tabId: RightRailTabId) {
   if (!tabId.startsWith('file:')) {
     return
   }
@@ -389,14 +386,8 @@ export function closeFilePreviewTab(tabId: RightRailTabId) {
   }
 }
 
-export function dismissFilePreviewTarget() {
-  closeFilePreviewTab($rightRailActiveTabId.get())
-}
-
-export function closeActiveRightRailTab() {
-  const activeTabId = $rightRailActiveTabId.get()
-
-  if (activeTabId === RIGHT_RAIL_PREVIEW_TAB_ID) {
+export function closeRightRailTab(tabId: RightRailTabId) {
+  if (tabId === RIGHT_RAIL_PREVIEW_TAB_ID) {
     if ($previewTarget.get()) {
       dismissPreviewTarget()
     }
@@ -404,11 +395,11 @@ export function closeActiveRightRailTab() {
     return
   }
 
-  if (activeTabId.startsWith('file:')) {
-    closeFilePreviewTab(activeTabId)
-  }
+  closeFilePreviewTab(tabId)
 }
 
+export const closeActiveRightRailTab = () => closeRightRailTab($rightRailActiveTabId.get())
+
 export function clearSessionPreviewRegistry() {
   $sessionPreviewRegistry.set({})
   setPreviewTarget(null)