diff --git a/apps/desktop/src/app/chat/sidebar/session-actions-menu.test.ts b/apps/desktop/src/app/chat/sidebar/session-actions-menu.test.ts
new file mode 100644
index 00000000000..321300ee8d3
--- /dev/null
+++ b/apps/desktop/src/app/chat/sidebar/session-actions-menu.test.ts
@@ -0,0 +1,92 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+import { $activeSessionId, $selectedStoredSessionId } from '@/store/session'
+
+import { renameSessionPreferringRpc } from './session-actions-menu'
+
+// The branched-session rename bug: a freshly branched session lives only in the
+// gateway's runtime _sessions map (no state.db row yet), so REST PATCH
+// /api/sessions/{id} 404s with "Session not found". renameSessionPreferringRpc
+// must route the ACTIVE row through the session.title RPC (runtime id), which
+// persists the row on demand, and otherwise fall back to REST.
+
+const renameSession = vi.fn(async () => ({ ok: true, title: 'rest-title' }))
+const request = vi.fn(async () => ({ title: 'rpc-title' }) as never)
+const activeGateway = vi.fn<() => { request: typeof request } | null>(() => ({ request }))
+
+vi.mock('@/hermes', () => ({
+  renameSession: (...args: unknown[]) => renameSession(...(args as [])),
+  HermesGateway: class {}
+}))
+
+vi.mock('@/store/gateway', () => ({
+  activeGateway: () => activeGateway()
+}))
+
+const RUNTIME_ID = 'rt-runtime-1'
+const STORED_ID = 'stored-branch-1'
+
+afterEach(() => {
+  renameSession.mockClear()
+  request.mockClear()
+  activeGateway.mockReset()
+  activeGateway.mockReturnValue({ request })
+  $activeSessionId.set(null)
+  $selectedStoredSessionId.set(null)
+})
+
+describe('renameSessionPreferringRpc', () => {
+  it('renames the active branched session via the session.title RPC, not REST', async () => {
+    $selectedStoredSessionId.set(STORED_ID)
+    $activeSessionId.set(RUNTIME_ID)
+
+    const result = await renameSessionPreferringRpc(STORED_ID, 'My branch')
+
+    expect(request).toHaveBeenCalledWith('session.title', { session_id: RUNTIME_ID, title: 'My branch' })
+    expect(renameSession).not.toHaveBeenCalled()
+    expect(result.title).toBe('rpc-title')
+  })
+
+  it('falls back to REST when the RPC fails (e.g. socket mid-reconnect)', async () => {
+    $selectedStoredSessionId.set(STORED_ID)
+    $activeSessionId.set(RUNTIME_ID)
+    request.mockRejectedValueOnce(new Error('not connected'))
+
+    const result = await renameSessionPreferringRpc(STORED_ID, 'My branch', 'work')
+
+    expect(request).toHaveBeenCalledOnce()
+    expect(renameSession).toHaveBeenCalledWith(STORED_ID, 'My branch', 'work')
+    expect(result.title).toBe('rest-title')
+  })
+
+  it('uses REST for a non-active row (background/persisted session)', async () => {
+    $selectedStoredSessionId.set('some-other-active-session')
+    $activeSessionId.set(RUNTIME_ID)
+
+    await renameSessionPreferringRpc(STORED_ID, 'My branch', 'work')
+
+    expect(request).not.toHaveBeenCalled()
+    expect(renameSession).toHaveBeenCalledWith(STORED_ID, 'My branch', 'work')
+  })
+
+  it('uses REST when clearing the title (RPC rejects empty titles)', async () => {
+    $selectedStoredSessionId.set(STORED_ID)
+    $activeSessionId.set(RUNTIME_ID)
+
+    await renameSessionPreferringRpc(STORED_ID, '')
+
+    expect(request).not.toHaveBeenCalled()
+    expect(renameSession).toHaveBeenCalledWith(STORED_ID, '', undefined)
+  })
+
+  it('uses REST when no gateway is connected', async () => {
+    $selectedStoredSessionId.set(STORED_ID)
+    $activeSessionId.set(RUNTIME_ID)
+    activeGateway.mockReturnValue(null)
+
+    await renameSessionPreferringRpc(STORED_ID, 'My branch')
+
+    expect(request).not.toHaveBeenCalled()
+    expect(renameSession).toHaveBeenCalledWith(STORED_ID, 'My branch', undefined)
+  })
+})