fix(desktop): resolve session usage footer by stored id with lineage match

CDP verification on the live app showed the footer never rendered: ChatView
passed the runtime id (view.$runtimeId) while $sessions rows key off stored
ids, and compression chains hand the view a lineage id rather than the row's
own id. Look up with selectedSessionId || routedSessionId and
sessionMatchesStoredId, same as ChatHeader.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/desktop/src/app/chat/index.tsx

@@ -697,9 +697,12 @@ const ChatViewContent = memo(function ChatViewContent({
   // memo'd Thread/ThreadMessageList, and a fresh element per render would
   // defeat their bail-out. Stats changes re-render inside SessionUsageFooter
   // via its own useStore($sessions) subscription, not through these props.
+  // The footer needs a STORED id ($sessions rows key off it): activeSessionId
+  // is the runtime id, so fall back through the routed id for fresh resumes.
+  const footerSessionId = selectedSessionId || routedSessionId
   const threadFooter = useMemo(
-    () => (activeSessionId ? <SessionUsageFooter sessionId={activeSessionId} /> : undefined),
-    [activeSessionId]
+    () => (footerSessionId ? <SessionUsageFooter sessionId={footerSessionId} /> : undefined),
+    [footerSessionId]
   )
 
   return (

apps/desktop/src/app/chat/session-usage-footer.test.tsx

@@ -58,6 +58,16 @@ describe('SessionUsageFooter', () => {
     expect(container.querySelector('[data-slot="session-usage-footer"]')).toBeNull()
   })
 
+  it('matches a live lineage id to the stored row, like the header does', () => {
+    // Auto-compression rotates the session id: the view holds a chain tip while
+    // the list row still carries its own id plus the lineage ids.
+    setSessions([makeSessionInfo({ _lineage_ids: ['root', 'tip'], id: 'root', input_tokens: 2_000, output_tokens: 400 })])
+
+    const { container } = render(<SessionUsageFooter sessionId="tip" />)
+
+    expect(container.querySelector('[data-slot="session-usage-footer"]')?.textContent).toContain('2.4k tok')
+  })
+
   it('re-renders when the sessions atom refreshes after a turn', () => {
     setSessions([makeSessionInfo({ id: 's1', input_tokens: 1_000, output_tokens: 200 })])
 

apps/desktop/src/app/chat/session-usage-footer.tsx

@@ -2,7 +2,7 @@ import { useStore } from '@nanostores/react'
 
 import { useI18n } from '@/i18n'
 import { compactNumber } from '@/lib/format'
-import { $sessions } from '@/store/session'
+import { $sessions, sessionMatchesStoredId } from '@/store/session'
 import { sessionCostUsd } from '@/store/sidebar-archive'
 
 /** Cumulative token/cost totals for one session, rendered at the end of the
@@ -13,7 +13,9 @@ import { sessionCostUsd } from '@/store/sidebar-archive'
 export function SessionUsageFooter({ sessionId }: { sessionId: string }) {
   const { t } = useI18n()
   const sessions = useStore($sessions)
-  const session = sessions.find(candidate => candidate.id === sessionId)
+  // Match like ChatHeader does: a compression chain hands the live view a
+  // lineage id, not necessarily the row's own id.
+  const session = sessions.find(candidate => sessionMatchesStoredId(candidate, sessionId))
 
   if (!session) {
     return null