fix(desktop): await gateway swap in selectProfile before requesting fresh session

[pcaruba]

Problem

When clicking a profile square in the desktop sidebar's ProfileRail, the profile pill highlights correctly but the chat continues talking to the old profile's agent. The user sees the new profile selected in the UI but their messages still go to the previous profile's backend.

Root cause

selectProfile() in store/profile.ts calls ensureGatewayProfile(target) with void (fire-and-forget), then immediately calls requestFreshSession() to navigate to a new chat. This creates a race condition:

1. void ensureGatewayProfile(target) starts the async gateway swap (spawning a pooled backend, establishing WebSocket)
2. requestFreshSession() runs synchronously — clears state, navigates to NEW_CHAT_ROUTE, shows a fresh draft
3. The gateway swap is still in flight — the secondary socket to the target profile's backend isn't connected yet
4. User types a message → createBackendSessionForSend does eventually await ensureGatewayProfile(), but by then the session state is already cleared and the fresh chat is rendered as ready

The same bug exists in newSessionInProfile().

Fix

Make selectProfile and newSessionInProfile async. When a real profile switch is happening (switching === true), await the gateway swap before calling requestFreshSession(). For the no-switch case (re-tapping the same profile), keep the fire-and-forget as a keepalive ping.

Changes

-export function selectProfile(name: string): void {
+export async function selectProfile(name: string): Promise<void> {
   ...
   if (switching) {
+    await ensureGatewayProfile(target)
     requestFreshSession()
-  }
-  void ensureGatewayProfile(target)
+  } else {
+    void ensureGatewayProfile(target)
+  }
}

-export function newSessionInProfile(name: string): void {
+export async function newSessionInProfile(name: string): Promise<void> {
   ...
+  await ensureGatewayProfile(target)
   requestFreshSession()
-  void ensureGatewayProfile(target)
 }

Related

• Add desktop profile switcher and stabilize composer scrolling #38157 "Add desktop profile switcher and stabilize composer scrolling" — takes a different approach (full window reload via mainWindow?.reload())
• feat: complete profile switcher — backend + frontend #33973 "feat: complete profile switcher — backend + frontend" — web dashboard only

[teknium1]

Thanks for the targeted profile-routing investigation. This is now redundant because current main fixes the wrong-profile behavior at the session-creation chokepoint rather than by delaying fresh-draft navigation.

• apps/desktop/src/app/session/hooks/use-session-actions/index.ts:194-195 resolves the selected profile and awaits ensureGatewayProfile() before creating a session.
• apps/desktop/src/app/session/hooks/use-session-actions/index.ts:218-226 sends that profile explicitly in session.create, so backend ownership does not depend on the ProfileRail reset timing.
• apps/desktop/src/app/session/hooks/use-session-actions.test.tsx:154-161 covers explicit per-profile creation routing.
• This was implemented in 79c3ed3cc91a53e910f403e7f026a1f4ef9c1f1c (fix(desktop): new chat honours the active profile instead of rubberbanding to default, shipped in v2026.6.19).

Automated hermes-sweeper review.