diff --git a/apps/desktop/electron/main.cjs b/apps/desktop/electron/main.cjs
index 2690ae450f7f2..581b032760dd5 100644
--- a/apps/desktop/electron/main.cjs
+++ b/apps/desktop/electron/main.cjs
@@ -5765,7 +5765,7 @@ function focusWindow(win) {
   win.focus()
 }
 
-function spawnSecondaryWindow({ sessionId, watch, newSession } = {}) {
+function spawnSecondaryWindow({ sessionId, watch, newSession, profile } = {}) {
   const icon = getAppIconPath()
   const win = new BrowserWindow({
     width: SESSION_WINDOW_MIN_WIDTH,
@@ -5810,7 +5810,8 @@ function spawnSecondaryWindow({ sessionId, watch, newSession } = {}) {
       devServer: DEV_SERVER,
       rendererIndexPath: DEV_SERVER ? undefined : resolveRendererIndex(),
       watch,
-      newSession
+      newSession,
+      profile
     })
   )
 
@@ -5818,8 +5819,8 @@ function spawnSecondaryWindow({ sessionId, watch, newSession } = {}) {
 }
 
 // Open (or focus) a standalone window for a single chat session.
-function createSessionWindow(sessionId, { watch = false } = {}) {
-  return sessionWindows.openOrFocus(sessionId, () => spawnSecondaryWindow({ sessionId, watch }))
+function createSessionWindow(sessionId, { watch = false, profile = null } = {}) {
+  return sessionWindows.openOrFocus(sessionId, () => spawnSecondaryWindow({ sessionId, watch, profile }))
 }
 
 // Open a fresh compact window on the new-session draft (#/). Not registry-keyed:
@@ -6148,7 +6149,10 @@ ipcMain.handle('hermes:window:openSession', async (_event, sessionId, opts) => {
     return { ok: false, error: 'invalid-session-id' }
   }
 
-  createSessionWindow(sessionId.trim(), { watch: opts?.watch === true })
+  createSessionWindow(sessionId.trim(), {
+    watch: opts?.watch === true,
+    profile: typeof opts?.profile === 'string' ? opts.profile.trim() : null
+  })
 
   return { ok: true }
 })
diff --git a/apps/desktop/electron/session-windows.cjs b/apps/desktop/electron/session-windows.cjs
index 5e2f3d4c680c7..ed072efaa9892 100644
--- a/apps/desktop/electron/session-windows.cjs
+++ b/apps/desktop/electron/session-windows.cjs
@@ -41,9 +41,26 @@ function chatWindowWebPreferences(preloadPath) {
 // onboarding overlays and the global session sidebar. `new=1` marks the compact
 // scratch window; `watch=1` marks a spectator window (e.g. a running subagent's
 // session): the renderer resumes it lazily so the gateway never builds an agent
-// just to stream into it.
-function buildSessionWindowUrl(sessionId, { devServer, rendererIndexPath, watch, newSession } = {}) {
-  const query = `?win=secondary${newSession ? '&new=1' : ''}${watch ? '&watch=1' : ''}`
+// just to stream into it. `profile` is a routing hint for multi-profile installs:
+// the new renderer process starts with empty in-memory stores, so it must not
+// race its first route resume against the wrong default-profile backend.
+function buildSessionWindowUrl(sessionId, { devServer, rendererIndexPath, watch, newSession, profile } = {}) {
+  const params = new URLSearchParams({ win: 'secondary' })
+  const profileHint = typeof profile === 'string' ? profile.trim() : ''
+
+  if (newSession) {
+    params.set('new', '1')
+  }
+
+  if (watch) {
+    params.set('watch', '1')
+  }
+
+  if (profileHint) {
+    params.set('profile', profileHint)
+  }
+
+  const query = `?${params.toString()}`
   const route = newSession ? '#/' : `#/${encodeURIComponent(sessionId)}`
 
   if (devServer) {
diff --git a/apps/desktop/electron/session-windows.test.cjs b/apps/desktop/electron/session-windows.test.cjs
index 78f19b859e411..53f1af3503cb1 100644
--- a/apps/desktop/electron/session-windows.test.cjs
+++ b/apps/desktop/electron/session-windows.test.cjs
@@ -86,6 +86,13 @@ test('buildSessionWindowUrl adds the watch flag for spectator windows, before th
   assert.equal(url, 'http://localhost:5173/?win=secondary&watch=1#/abc')
 })
 
+test('buildSessionWindowUrl carries a profile hint before the hash route', () => {
+  const url = buildSessionWindowUrl('abc', { devServer: 'http://localhost:5173', profile: 'mission control' })
+
+  assert.equal(url, 'http://localhost:5173/?win=secondary&profile=mission+control#/abc')
+  assert.ok(url.indexOf('profile=mission+control') < url.indexOf('#'))
+})
+
 test('buildSessionWindowUrl routes new-session windows to the draft (#/)', () => {
   const url = buildSessionWindowUrl(null, { devServer: 'http://localhost:5173', newSession: true })
 
diff --git a/apps/desktop/src/app/chat/index.tsx b/apps/desktop/src/app/chat/index.tsx
index a5216210a7996..bdf65be094a49 100644
--- a/apps/desktop/src/app/chat/index.tsx
+++ b/apps/desktop/src/app/chat/index.tsx
@@ -147,6 +147,7 @@ function ChatHeader({
           onDelete={selectedSessionId ? onDeleteSelectedSession : undefined}
           onPin={selectedSessionId ? onToggleSelectedPin : undefined}
           pinned={selectedIsPinned}
+          profile={activeStoredSession?.profile}
           sessionId={selectedSessionId || activeSessionId || ''}
           sideOffset={8}
           title={title}
diff --git a/apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx b/apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx
index 08c13550a4356..91d1efb9f423b 100644
--- a/apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx
+++ b/apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx
@@ -126,7 +126,7 @@ function useSessionActions({
             label: r.newWindow,
             onSelect: () => {
               triggerHaptic('selection')
-              void openSessionInNewWindow(sessionId)
+              void openSessionInNewWindow(sessionId, { profile })
             }
           }
         ]
diff --git a/apps/desktop/src/app/chat/sidebar/session-row.tsx b/apps/desktop/src/app/chat/sidebar/session-row.tsx
index d2543b9058aa7..f8b2940eff0cf 100644
--- a/apps/desktop/src/app/chat/sidebar/session-row.tsx
+++ b/apps/desktop/src/app/chat/sidebar/session-row.tsx
@@ -171,7 +171,7 @@ export function SidebarSessionRow({
               event.preventDefault()
               event.stopPropagation()
               triggerHaptic('selection')
-              void openSessionInNewWindow(session.id)
+              void openSessionInNewWindow(session.id, { profile: session.profile })
 
               return
             }
diff --git a/apps/desktop/src/app/session/hooks/use-session-actions/index.ts b/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
index 0f88fc9481003..59e2c44ba91e7 100644
--- a/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
+++ b/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
@@ -42,7 +42,7 @@ import {
   workspaceCwdForNewSession
 } from '@/store/session'
 import { broadcastSessionsChanged } from '@/store/session-sync'
-import { isWatchWindow } from '@/store/windows'
+import { isWatchWindow, sessionWindowProfile } from '@/store/windows'
 import type { SessionCreateResponse, SessionResumeResponse, UsageStats } from '@/types/hermes'
 
 import { NEW_CHAT_ROUTE, sessionRoute, SETTINGS_ROUTE } from '../../../routes'
@@ -343,8 +343,9 @@ export function useSessionActions({
       // gateway call (no-op when it's already on that profile / single-profile).
       // resolveStoredSession finds the row by id (cheap), so an uncached pasted
       // id loads as fast as a sidebar click instead of hanging on a list scan.
-      const storedForProfile = await resolveStoredSession(storedSessionId)
-      const sessionProfile = storedForProfile?.profile
+      const profileHint = sessionWindowProfile()
+      const storedForProfile = await resolveStoredSession(storedSessionId, profileHint)
+      const sessionProfile = storedForProfile?.profile ?? profileHint
 
       if (resumeRequestRef.current !== requestId) {
         return
diff --git a/apps/desktop/src/app/session/hooks/use-session-actions/utils.test.ts b/apps/desktop/src/app/session/hooks/use-session-actions/utils.test.ts
index 680cc754286e0..821cd02c3510f 100644
--- a/apps/desktop/src/app/session/hooks/use-session-actions/utils.test.ts
+++ b/apps/desktop/src/app/session/hooks/use-session-actions/utils.test.ts
@@ -1,12 +1,15 @@
-import { describe, expect, it } from 'vitest'
+import { afterEach, describe, expect, it, vi } from 'vitest'
 
 import type { ChatMessage } from '@/lib/chat-messages'
+import { $activeGatewayProfile, $profiles } from '@/store/profile'
+import { $sessions } from '@/store/session'
 import type { SessionInfo } from '@/types/hermes'
 
 import {
   chatMessageArraysEquivalent,
   isSessionGoneError,
   reconcileResumeMessages,
+  resolveStoredSession,
   sessionMatchesStoredId,
   sessionShouldHaveTranscript,
   toBranchMessages
@@ -17,6 +20,14 @@ const msg = (id: string, role: ChatMessage['role'], text: string, extra: Partial
 
 const session = (over: Partial<SessionInfo>): SessionInfo => over as SessionInfo
 
+afterEach(() => {
+  $activeGatewayProfile.set('default')
+  $profiles.set([])
+  $sessions.set([])
+  vi.restoreAllMocks()
+  Reflect.deleteProperty(window, 'hermesDesktop')
+})
+
 describe('isSessionGoneError', () => {
   it('is true for 404 / session-not-found, false otherwise', () => {
     expect(isSessionGoneError(new Error('Request failed 404'))).toBe(true)
@@ -42,6 +53,25 @@ describe('sessionShouldHaveTranscript', () => {
   })
 })
 
+describe('resolveStoredSession', () => {
+  it('uses a session-window profile hint before probing the active/default backend', async () => {
+    const api = vi.fn(async (request: { path: string; profile?: string | null }) => {
+      expect(request.profile).toBe('mission-control')
+      expect(request.path).toBe('/api/sessions/s1?profile=mission-control')
+
+      return session({ id: 's1', message_count: 2, title: 'Mission' })
+    })
+
+    ;(window as unknown as { hermesDesktop?: unknown }).hermesDesktop = { api }
+
+    const resolved = await resolveStoredSession('s1', 'mission-control')
+
+    expect(api).toHaveBeenCalledTimes(1)
+    expect(resolved).toMatchObject({ id: 's1', profile: 'mission-control' })
+    expect($sessions.get()[0]).toMatchObject({ id: 's1', profile: 'mission-control' })
+  })
+})
+
 describe('toBranchMessages', () => {
   it('keeps only user/assistant turns that carry text', () => {
     const out = toBranchMessages([
diff --git a/apps/desktop/src/app/session/hooks/use-session-actions/utils.ts b/apps/desktop/src/app/session/hooks/use-session-actions/utils.ts
index 254a58e1298a5..dc0fc72a406d1 100644
--- a/apps/desktop/src/app/session/hooks/use-session-actions/utils.ts
+++ b/apps/desktop/src/app/session/hooks/use-session-actions/utils.ts
@@ -205,13 +205,37 @@ function upsertResolvedSession(session: SessionInfo, storedSessionId: string) {
   ])
 }
 
-export async function resolveStoredSession(storedSessionId: string): Promise<SessionInfo | undefined> {
+function withResolvedProfile(session: SessionInfo, profile: string | null | undefined): SessionInfo {
+  const key = normalizeProfileKey(profile)
+
+  return session.profile ? session : { ...session, profile: key }
+}
+
+export async function resolveStoredSession(
+  storedSessionId: string,
+  profileHint?: string | null
+): Promise<SessionInfo | undefined> {
   const cached = $sessions.get().find(session => sessionMatchesStoredId(session, storedSessionId))
 
   if (cached) {
     return cached
   }
 
+  const hintedProfile = profileHint?.trim()
+
+  if (hintedProfile) {
+    try {
+      const session = withResolvedProfile(await getSession(storedSessionId, hintedProfile), hintedProfile)
+
+      upsertResolvedSession(session, storedSessionId)
+
+      return session
+    } catch {
+      // Stale or invalid hint — fall through to the legacy active/cross-profile
+      // lookup so old windows and copied URLs remain recoverable.
+    }
+  }
+
   // Direct by-id on the live backend — one row lookup, no list scan. Covers
   // single-profile users and any id on the active profile (e.g. an old session
   // past the sidebar's recent window). 404 just means it's not on this profile.
@@ -237,7 +261,7 @@ export async function resolveStoredSession(storedSessionId: string): Promise<Ses
 
   for (const profile of otherProfiles) {
     try {
-      const session = await getSession(storedSessionId, profile)
+      const session = withResolvedProfile(await getSession(storedSessionId, profile), profile)
 
       upsertResolvedSession(session, storedSessionId)
 
diff --git a/apps/desktop/src/global.d.ts b/apps/desktop/src/global.d.ts
index 870d3311837e8..de836496ef58b 100644
--- a/apps/desktop/src/global.d.ts
+++ b/apps/desktop/src/global.d.ts
@@ -30,7 +30,10 @@ declare global {
       // with an error code when the sessionId is empty/invalid. `watch` opens
       // a spectator window (lazy resume — no agent build) for live-streaming
       // a running subagent's session.
-      openSessionWindow: (sessionId: string, opts?: { watch?: boolean }) => Promise<{ ok: boolean; error?: string }>
+      openSessionWindow: (
+        sessionId: string,
+        opts?: { watch?: boolean; profile?: string | null }
+      ) => Promise<{ ok: boolean; error?: string }>
       // Open (or focus) a compact secondary window on the new-session draft.
       openNewSessionWindow: () => Promise<{ ok: boolean; error?: string }>
       // The pop-out pet overlay: a transparent always-on-top window hosting only
diff --git a/apps/desktop/src/store/windows.test.ts b/apps/desktop/src/store/windows.test.ts
index 28ae3cc39c9f0..8789c3809fae7 100644
--- a/apps/desktop/src/store/windows.test.ts
+++ b/apps/desktop/src/store/windows.test.ts
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { canOpenSessionWindow, openNewSessionInNewWindow, openSessionInNewWindow } from './windows'
+import { canOpenSessionWindow, openNewSessionInNewWindow, openSessionInNewWindow, sessionWindowProfile } from './windows'
 
 const desktopWindow = window as unknown as { hermesDesktop?: Window['hermesDesktop'] }
 const initialHermesDesktop = desktopWindow.hermesDesktop
@@ -89,6 +89,16 @@ describe('openSessionInNewWindow', () => {
     expect(notifyError).not.toHaveBeenCalled()
   })
 
+  it('forwards the profile hint for multi-profile session windows', async () => {
+    const open = vi.fn().mockResolvedValue({ ok: true })
+    installBridge(open)
+
+    await openSessionInNewWindow('s1', { profile: 'mission-control' })
+
+    expect(open).toHaveBeenCalledWith('s1', { profile: 'mission-control' })
+    expect(notifyError).not.toHaveBeenCalled()
+  })
+
   it('notifies on an ok:false result', async () => {
     installBridge(vi.fn().mockResolvedValue({ ok: false, error: 'invalid-session-id' }))
 
@@ -141,3 +151,11 @@ describe('openNewSessionInNewWindow', () => {
     expect(notifyError).toHaveBeenCalledTimes(1)
   })
 })
+
+describe('sessionWindowProfile', () => {
+  it('reads the profile hint from the pre-hash query string', () => {
+    window.history.replaceState(null, '', '/?win=secondary&profile=mission-control#/s1')
+
+    expect(sessionWindowProfile()).toBe('mission-control')
+  })
+})
diff --git a/apps/desktop/src/store/windows.ts b/apps/desktop/src/store/windows.ts
index c5b36ca68554c..ce500597b3940 100644
--- a/apps/desktop/src/store/windows.ts
+++ b/apps/desktop/src/store/windows.ts
@@ -7,6 +7,7 @@ import { notifyError } from './notifications'
 // global session sidebar or the install / onboarding overlays.
 const SECONDARY_WINDOW_FLAG = 'secondary'
 const NEW_SESSION_WINDOW_FLAG = '1'
+const PROFILE_WINDOW_PARAM = 'profile'
 
 let secondaryWindowCache: boolean | null = null
 
@@ -72,6 +73,26 @@ export function isWatchWindow(): boolean {
   return result
 }
 
+let sessionWindowProfileCache: string | null | undefined
+
+export function sessionWindowProfile(): string | null {
+  if (sessionWindowProfileCache !== undefined) {
+    return sessionWindowProfileCache
+  }
+
+  let result: string | null = null
+
+  try {
+    result = new URLSearchParams(window.location.search).get(PROFILE_WINDOW_PARAM)?.trim() || null
+  } catch {
+    result = null
+  }
+
+  sessionWindowProfileCache = result
+
+  return result
+}
+
 // True when running inside the Electron desktop shell (the preload bridge is
 // present). The "open in new window" affordance is desktop-only.
 export function canOpenSessionWindow(): boolean {
@@ -97,7 +118,10 @@ async function openWindow(call: () => Promise<WindowOpenResult>, failMessage: st
 // Open (or focus) a standalone OS window for a single chat session. No-ops
 // gracefully outside Electron so callers can wire it unconditionally.
 // `watch: true` opens a spectator window (lazy resume, live-mirror stream).
-export async function openSessionInNewWindow(sessionId: string, opts?: { watch?: boolean }): Promise<void> {
+export async function openSessionInNewWindow(
+  sessionId: string,
+  opts?: { watch?: boolean; profile?: string | null }
+): Promise<void> {
   if (!sessionId || !canOpenSessionWindow()) {
     return
   }