Performance audit: identified hotspots in desktop app

[Copilot]

Follow-up to the perf-log instrumentation: a static walk of apps/desktop/ to actually name the bottlenecks, with file:line citations. No code changes in this PR — review the findings, then I'll open targeted fixes.

P0 — "the longer it runs, the slower it gets"

• Workspace never unmounts. App.tsx:593-604 toggles display:none instead of unmounting, so every Workspace effect keeps running on Settings/History/Analytics tabs.
• RuntimeOverviewCard polls 3 IPCs every 7s with no isActive gate. components/workspace/RuntimeOverviewCard.tsx:111-113. Only checks document.visibilityState.
• Per-bubble 1s timer runs in background. components/workspace/WorkspaceMessageBubble.tsx:845 — setInterval(() => setNow(Date.now()), 1000) on every streaming bubble, regardless of tab/visibility.
• Overlapping pollers, unaligned periods. 2.5s / 3s / 3s / 5s / 7s across InteractiveToolEventsPanel:193, HeadlessSessionsPanel:198, useWorkspaceSessionDecorations.ts:467, pages/Sessions.tsx:260, RuntimeOverviewCard.tsx:111. Most duplicate already-wired listen() event streams.

P1 — long-conversation jank

• MarkdownRenderer is not memoized and passes an inline components={{...}} to react-markdown. components/history/MarkdownRenderer.tsx:313-326. New object identity every parent render → full markdown subtree (incl. Prism) re-renders for every visible bubble. Single biggest contributor to scroll/segment-switch jank.
• History only grows. components/history/HistoryDetail.tsx:79-103 — renderedMessageCount increments via IntersectionObserver but older messages never unmount. No virtualization library in package.json.
• ProxyDebug rebuilds the full list per event. pages/ProxyDebug.tsx:118-122 — [payload, ...prev.filter(i => i.id !== payload.id)].slice(0, 200) runs O(n) on every proxy-traffic event.

P2

• 7 useAppStore call sites missing shallow — notably high-churn HeadlessSessionsPanel and WorkspaceNativeSessionView (×2). Also BindToChatDialog, AiCronPanel, PetEntry, BindToTelegramDialog, SessionsCard.
• focus-sync chain redundant with event bus. App.tsx:401-460 fires loadCurrentEnv + loadEnvironments (+ loadSessions) on every refocus despite env-changed / perm-changed event coverage.

P3

• backdrop-filter surface area — already mitigated by performanceMode='reduced', not the primary issue.
• CronTasks (1226 LOC) / Sessions (924) / Skills (601) lack virtualization. Memoization gains first.

Suggested fix sequence

1. First PR (smallest, biggest payoff): isActive gate on RuntimeOverviewCard + memo(MarkdownRenderer) with components hoisted to module scope + add shallow to the 7 sites.
2. Second PR: unify pollers behind usePoll(fn, ms, { active, visibilityGated, idle }); gate the per-bubble 1s timer on streaming && visible; ProxyDebug → Map<id, item> + useDeferredValue.
3. Third PR: focus-sync → staleness-triggered; evaluate @tanstack/react-virtual for History once re-render storms are gone; add Rust-side tracing on the high-frequency commands surfaced by perf-log.

Want me to proceed with step 1?