fix(desktop): give ⌘T session tabs a live gateway so slash completions load

`useGatewayRequest` only exposed the gateway through a ref that its own
subscription effect fills in, so a component reading it during render saw
null on mount. Session tiles — what ⌘T and the tab-strip "+" open — did
exactly that and passed `gateway={null}` down to ChatBar. The slash
adapter is disabled without a gateway, so a new tab had no completions at
all while ⌘N, which resolves its gateway through a state-driven memo,
worked fine. Nothing re-rendered the tile afterwards unless the connection
state happened to flip, so it never recovered.

Return the `$gateway` atom as a reactive value alongside the ref and use
it wherever the gateway is needed as a render-time value. The ref stays
for `requestGateway`, which wants a stable identity. The model picker,
model visibility, and settings overlays read the same ref during render,
so they're moved over too.

apps/desktop/src/app/chat/session-tile.tsx

@@ -113,7 +113,7 @@ function TileChat({
   storedSessionId: string
   view: SessionView
 }) {
-  const { gatewayRef, requestGateway } = useGatewayRequest()
+  const { gateway, requestGateway } = useGatewayRequest()
   const queryClient = useQueryClient()
   const { selectModel } = useModelControls({ queryClient, requestGateway })
   const activeGatewayProfile = useStore($activeGatewayProfile)
@@ -151,20 +151,20 @@ function TileChat({
     () =>
       gatewayOpen ? (
         <ModelMenuPanel
-          gateway={gatewayRef.current || undefined}
+          gateway={gateway || undefined}
           onSelectModel={selectModel}
           profile={activeGatewayProfile}
           requestGateway={requestGateway}
         />
       ) : null,
-    [activeGatewayProfile, gatewayOpen, gatewayRef, requestGateway, selectModel]
+    [activeGatewayProfile, gateway, gatewayOpen, requestGateway, selectModel]
   )
 
   return (
     <SessionViewProvider value={view}>
       <ComposerScopeProvider value={scope}>
         <ChatView
-          gateway={gatewayRef.current}
+          gateway={gateway}
           modelMenuContent={modelMenuContent}
           onAddContextRef={composer.addContextRefAttachment}
           onAddUrl={url => composer.addContextRefAttachment(`@url:${formatRefValue(url)}`, url)}

apps/desktop/src/app/contrib/wiring.tsx

@@ -222,7 +222,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
     setMessages
   })
 
-  const { connectionRef, gatewayRef, requestGateway } = useGatewayRequest()
+  const { connectionRef, gateway, gatewayRef, requestGateway } = useGatewayRequest()
 
   const {
     loadMoreMessagingForPlatform,
@@ -943,13 +943,13 @@ export function ContribWiring({ children }: { children: ReactNode }) {
         />
       )}
       <ModelPickerOverlay
-        gateway={gatewayRef.current || undefined}
+        gateway={gateway || undefined}
         onSelect={selectModel}
         profile={activeGatewayProfile}
       />
       <SessionPickerOverlay onResume={resumeSession} />
       <ModelVisibilityOverlay
-        gateway={gatewayRef.current || undefined}
+        gateway={gateway || undefined}
         onOpenProviders={openProviderSettings}
         profile={activeGatewayProfile}
       />
@@ -965,7 +965,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
       {settingsOpen && (
         <Suspense fallback={null}>
           <SettingsView
-            gateway={gatewayRef.current}
+            gateway={gateway}
             onClose={closeOverlayToPreviousRoute}
             onConfigSaved={() => {
               void refreshHermesConfig()

apps/desktop/src/app/gateway/hooks/use-gateway-request.test.ts

@@ -0,0 +1,39 @@
+import { act, renderHook } from '@testing-library/react'
+import { afterEach, describe, expect, it } from 'vitest'
+
+import type { HermesGateway } from '@/hermes'
+import { $gateway } from '@/store/gateway'
+
+import { useGatewayRequest } from './use-gateway-request'
+
+const fakeGateway = { connectionState: 'open' } as unknown as HermesGateway
+
+afterEach(() => {
+  $gateway.set(null)
+})
+
+describe('useGatewayRequest', () => {
+  // The composer's `/` completions only exist when ChatBar receives a non-null
+  // gateway PROP. `gatewayRef` is populated by a subscription effect, so it is
+  // still null on the first render — a surface that read the ref while
+  // rendering (session tiles / ⌘T tabs) shipped `gateway={null}` and silently
+  // lost slash completions. The returned `gateway` value must be live
+  // immediately so that never happens again.
+  it('exposes the live gateway on the first render, before effects run', () => {
+    $gateway.set(fakeGateway)
+
+    const { result } = renderHook(() => useGatewayRequest())
+
+    expect(result.current.gateway).toBe(fakeGateway)
+  })
+
+  it('tracks the gateway when the active socket changes', () => {
+    const { result } = renderHook(() => useGatewayRequest())
+
+    expect(result.current.gateway).toBeNull()
+
+    act(() => $gateway.set(fakeGateway))
+
+    expect(result.current.gateway).toBe(fakeGateway)
+  })
+})

apps/desktop/src/app/gateway/hooks/use-gateway-request.ts

@@ -9,6 +9,14 @@ import { $gatewayState, setConnection } from '@/store/session'
 
 export function useGatewayRequest() {
   const gatewayState = useStore($gatewayState)
+  // Reactive companion to `gatewayRef`. The ref exists so `requestGateway`
+  // keeps a stable identity and always reaches the live socket, but it is only
+  // populated by the subscription effect below — i.e. AFTER the first render.
+  // A component that reads `gatewayRef.current` while rendering therefore sees
+  // null on mount, and if the connection state doesn't happen to flip
+  // afterwards it never re-renders to pick the instance up. Anything that needs
+  // the gateway as a render-time VALUE (props, memo deps) must use this.
+  const gateway = useStore($gateway) as HermesGateway | null
   const gatewayRef = useRef<HermesGateway | null>(null)
 
   const connectionRef = useRef<Awaited<ReturnType<NonNullable<typeof window.hermesDesktop>['getConnection']>> | null>(
@@ -136,5 +144,5 @@ export function useGatewayRequest() {
     [ensureGatewayOpen]
   )
 
-  return { connectionRef, gatewayRef, requestGateway }
+  return { connectionRef, gateway, gatewayRef, requestGateway }
 }