perf(desktop): pause hidden-pane timers in agents view, cron sidebar, and floating pet

Partial pick of the surviving renderer hunks from #75395 (perf commit
6502e441d plus fixup 3fbbc9c1d): gate the 500ms subagent now-ticker and
the cron sidebar 1s ticker/run-poll on usePaneVisible, and skip the
legacy floating-pet poll while the document is hidden. Dropped hunks
(electron/main.ts, vitest.setup.ts/config) intentionally excluded.

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

@@ -1,6 +1,7 @@
 import { useStore } from '@nanostores/react'
 import { type ReactNode, useEffect, useMemo, useState } from 'react'
 
+import { usePaneVisible } from '@/components/pane-shell/pane-visibility'
 import { useElapsedSeconds } from '@/components/chat/activity-timer'
 import { ActivityTimerText } from '@/components/chat/activity-timer-text'
 import { Codicon } from '@/components/ui/codicon'
@@ -189,15 +190,17 @@ function SubagentTree({ tree }: { tree: SubagentNode[] }) {
   const tokens = flat.reduce((sum, n) => sum + (n.inputTokens ?? 0) + (n.outputTokens ?? 0), 0)
   const cost = flat.reduce((sum, n) => sum + (n.costUsd ?? 0), 0)
 
+  const visible = usePaneVisible()
+
   useEffect(() => {
-    if (active <= 0 || typeof window === 'undefined') {
+    if (active <= 0 || !visible || typeof window === 'undefined') {
       return
     }
 
     const id = window.setInterval(() => setNowMs(Date.now()), 500)
 
     return () => window.clearInterval(id)
-  }, [active])
+  }, [active, visible])
 
   if (tree.length === 0) {
     return (

apps/desktop/src/app/chat/sidebar/cron-jobs-section.tsx

@@ -1,6 +1,8 @@
 import { useStore } from '@nanostores/react'
 import { useEffect, useMemo, useState } from 'react'
 
+import { usePaneVisible } from '@/components/pane-shell/pane-visibility'
+
 import { ActionsContextMenu, type MenuKit, renderActionItem } from '@/components/ui/actions-menu'
 import { Codicon } from '@/components/ui/codicon'
 import { DisclosureCaret } from '@/components/ui/disclosure-caret'
@@ -92,17 +94,19 @@ export function SidebarCronJobsSection({
   // Rows revealed so far; starts compact, grows in steps via "load more".
   const [visibleCount, setVisibleCount] = useState(INITIAL_VISIBLE_JOBS)
 
+  const visible = usePaneVisible()
+
   // One clock for the whole section (rows are pure) so the countdowns tick
-  // without re-rendering the rest of the sidebar. Only runs while expanded.
+  // without re-rendering the rest of the sidebar. Only runs while expanded and visible.
   useEffect(() => {
-    if (!open) {
+    if (!open || !visible) {
       return
     }
 
     const id = window.setInterval(() => setNowMs(Date.now()), 1000)
 
     return () => window.clearInterval(id)
-  }, [open])
+  }, [open, visible])
 
   // Upcoming first (soonest next run), jobs with no next run sink to the bottom,
   // then alphabetical for stability.
@@ -328,6 +332,7 @@ function CronJobSidebarRuns({ jobId, onOpenRun }: { jobId: string; onOpenRun: (s
   const changeEventsAvailable = useStore($changeEventsAvailable)
   const cronChangeTick = useStore($cronChangeTick)
   const [runs, setRuns] = useState<null | SessionInfo[]>(null)
+  const visible = usePaneVisible()
 
   useEffect(() => {
     let cancelled = false
@@ -345,11 +350,14 @@ function CronJobSidebarRuns({ jobId, onOpenRun }: { jobId: string; onOpenRun: (s
           }
         })
 
-    void load()
+    // Initial load when visible
+    if (visible) {
+      void load()
+    }
 
     const intervalId = window.setInterval(
       () => {
-        if (document.visibilityState === 'visible') {
+        if (visible && document.visibilityState === 'visible') {
           void load()
         }
       },
@@ -361,7 +369,7 @@ function CronJobSidebarRuns({ jobId, onOpenRun }: { jobId: string; onOpenRun: (s
       window.clearInterval(intervalId)
     }
     // cronChangeTick: a fired run reloads the peek immediately.
-  }, [changeEventsAvailable, cronChangeTick, jobId])
+  }, [changeEventsAvailable, cronChangeTick, jobId, visible])
 
   return (
     <div className="mb-1 ml-[1.375rem] flex flex-col gap-px">

apps/desktop/src/components/pet/floating-pet.tsx

@@ -214,7 +214,11 @@ export function FloatingPet() {
     // so no timer. Legacy backend: the historical poll.
     const timer = changeEventsAvailable
       ? null
-      : window.setInterval(() => void pull(), active ? PET_ACTIVE_REFRESH_MS : PET_POLL_MS)
+      : window.setInterval(() => {
+          if (document.visibilityState === 'visible') {
+            void pull()
+          }
+        }, active ? PET_ACTIVE_REFRESH_MS : PET_POLL_MS)
 
     return () => {
       cancelled = true