fix(desktop): fall back to the engine's most recent session when the boot-restored chat is dead

apps/desktop/src/app/desktop-controller-utils.test.ts

@@ -2,10 +2,13 @@ import { describe, expect, it } from 'vitest'
 
 import type { SessionInfo } from '@/hermes'
 
-import { sameCronSignature } from './desktop-controller-utils'
+import { pickMostRecentSessionId, sameCronSignature } from './desktop-controller-utils'
 
 const session = (id: string, title: string | null): SessionInfo => ({ id, title }) as SessionInfo
 
+const recent = (id: string, over: Partial<SessionInfo> = {}): SessionInfo =>
+  ({ id, archived: false, is_active: false, last_active: 0, ...over }) as SessionInfo
+
 describe('sameCronSignature', () => {
   it('is false when the lengths differ', () => {
     expect(sameCronSignature([session('a', 't')], [])).toBe(false)
@@ -29,3 +32,39 @@ describe('sameCronSignature', () => {
     expect(sameCronSignature(a, b)).toBe(false)
   })
 })
+
+describe('pickMostRecentSessionId', () => {
+  it('returns null for an empty list', () => {
+    expect(pickMostRecentSessionId([], null)).toBeNull()
+  })
+
+  it('picks the newest session by last_active', () => {
+    const sessions = [recent('old', { last_active: 100 }), recent('new', { last_active: 300 }), recent('mid', { last_active: 200 })]
+    expect(pickMostRecentSessionId(sessions, null)).toBe('new')
+  })
+
+  it('prefers an active session over a newer inactive one', () => {
+    const sessions = [recent('live', { is_active: true, last_active: 100 }), recent('newer-but-ended', { last_active: 900 })]
+    expect(pickMostRecentSessionId(sessions, null)).toBe('live')
+  })
+
+  it('skips archived sessions', () => {
+    const sessions = [recent('archived-new', { archived: true, last_active: 900 }), recent('plain-old', { last_active: 100 })]
+    expect(pickMostRecentSessionId(sessions, null)).toBe('plain-old')
+  })
+
+  it('excludes the stale session by stored id and by lineage root', () => {
+    const sessions = [
+      recent('dead', { last_active: 900 }),
+      recent('dead-tip', { _lineage_root_id: 'dead', last_active: 800 }),
+      recent('alive', { last_active: 100 })
+    ]
+
+    expect(pickMostRecentSessionId(sessions, 'dead')).toBe('alive')
+  })
+
+  it('returns null when everything is excluded or archived', () => {
+    const sessions = [recent('dead', { last_active: 900 }), recent('gone', { archived: true, last_active: 800 })]
+    expect(pickMostRecentSessionId(sessions, 'dead')).toBeNull()
+  })
+})

apps/desktop/src/app/desktop-controller-utils.ts

@@ -1,5 +1,38 @@
 import type { SessionInfo } from '@/hermes'
 
+/**
+ * Engine-most-recent fallback for a cold-boot restore whose pinned session id
+ * turned out to be dead (deleted/rotated while the app was closed). Prefers a
+ * currently-active session (a runtime is live on it right now), then the
+ * newest by last_active; skips archived rows and the dead session itself —
+ * matched by stored id or lineage root, mirroring sessionMatchesStoredId().
+ * Returns null when nothing qualifies (caller falls back to the new-chat
+ * route).
+ */
+export function pickMostRecentSessionId(sessions: SessionInfo[], excludeStoredId: null | string): null | string {
+  let best: null | SessionInfo = null
+
+  for (const session of sessions) {
+    if (session.archived) {
+      continue
+    }
+
+    if (excludeStoredId && (session.id === excludeStoredId || session._lineage_root_id === excludeStoredId)) {
+      continue
+    }
+
+    if (
+      !best ||
+      (session.is_active && !best.is_active) ||
+      (session.is_active === best.is_active && (session.last_active ?? 0) > (best.last_active ?? 0))
+    ) {
+      best = session
+    }
+  }
+
+  return best?.id ?? null
+}
+
 // Cheap signature compare so a poll only swaps the atom (and re-renders the
 // sidebar) when the visible rows actually changed.
 export function sameCronSignature(a: SessionInfo[], b: SessionInfo[]): boolean {

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

@@ -88,6 +88,7 @@ import {
 } from './chat/right-rail'
 import { ChatSidebar } from './chat/sidebar'
 import { CommandPalette } from './command-palette'
+import { pickMostRecentSessionId } from './desktop-controller-utils'
 import { useGatewayBoot } from './gateway/hooks/use-gateway-boot'
 import { useGatewayRequest } from './gateway/hooks/use-gateway-request'
 import { useKeybinds } from './hooks/use-keybinds'
@@ -278,9 +279,11 @@ export function DesktopController() {
   }, [routedSessionId])
 
   // Restore that chat once, on cold start only (we're at the new-chat route and
-  // haven't navigated yet). A dead/deleted id self-clears via the exhausted latch
-  // below, so we never boot-loop into an error screen.
+  // haven't navigated yet). The restore is optimistic — the pinned id is not
+  // validated first, so the happy path costs no round trip and no new-chat
+  // flash. A dead/deleted id self-heals via the exhausted latch below.
   const restoredLastSessionRef = useRef(false)
+  const bootRestoredSessionIdRef = useRef<null | string>(null)
   useEffect(() => {
     if (restoredLastSessionRef.current) {
       return
@@ -290,15 +293,41 @@ export function DesktopController() {
     const last = getRememberedSessionId()
 
     if (last && location.pathname === NEW_CHAT_ROUTE) {
+      bootRestoredSessionIdRef.current = last
       navigate(sessionRoute(last), { replace: true })
     }
   }, [location.pathname, navigate])
 
+  // Once the user routes anywhere else, the boot restore is no longer ours to
+  // correct — coming back to that session later is a deliberate open and keeps
+  // the normal error + Retry UI if it turns out dead.
   useEffect(() => {
-    if (resumeExhaustedSessionId && getRememberedSessionId() === resumeExhaustedSessionId) {
+    if (bootRestoredSessionIdRef.current && routedSessionId && routedSessionId !== bootRestoredSessionIdRef.current) {
+      bootRestoredSessionIdRef.current = null
+    }
+  }, [routedSessionId])
+
+  useEffect(() => {
+    if (!resumeExhaustedSessionId) {
+      return
+    }
+
+    if (getRememberedSessionId() === resumeExhaustedSessionId) {
       setRememberedSessionId(null)
     }
-  }, [resumeExhaustedSessionId])
+
+    // The session this window cold-booted onto proved dead (the exhausted
+    // latch only arms with the gateway open, after the bounded resume retries
+    // gave up — so this is a stale pin, not a down backend). Fall back to the
+    // engine's most recent session instead of stranding the boot on an error
+    // screen the user never chose. Sessions the user opened deliberately keep
+    // the explicit error + Retry UI — this fires only for the boot restore.
+    if (bootRestoredSessionIdRef.current === resumeExhaustedSessionId && routedSessionId === resumeExhaustedSessionId) {
+      bootRestoredSessionIdRef.current = null
+      const fallback = pickMostRecentSessionId($sessions.get(), resumeExhaustedSessionId)
+      navigate(fallback ? sessionRoute(fallback) : NEW_CHAT_ROUTE, { replace: true })
+    }
+  }, [resumeExhaustedSessionId, routedSessionId, navigate])
 
   // Notification click: the main process already focused the window; jump to its
   // session. Notifications are tagged with the gateway *runtime* session id, but