perf: reduce UI render fanout and scroll jitter

- Cut broad render fanout across the app by replacing shared-store whole-object subscriptions with leaf selectors, memoizing hot chrome boundaries, and isolating disabled global providers from live session/message state. This keeps header controls, composer toolbars, side panels, and other non-hot UI surfaces from repainting on every assistant update or keystroke.

- Rework sidebar session ordering so recent, project groups, and worktree groups derive from one ordering source while avoiding streaming-time thrash. The sidebar now uses a stabilized session snapshot, preserves structural identity for unchanged rows, reads live row status/details per session, and applies a one-shot sort bump on idle->busy instead of continuously resorting during activity.

- Fix chat/input scroll instability by separating viewport-resize handling from message-growth handling, disabling conflicting native scroll anchoring, and stopping textarea autosize from collapsing on every growth keystroke. This removes the multiline typing jiggle during streaming and reduces unnecessary composer rerenders.

- Also gate voice context wiring behind voice-mode enablement and codify the learned render/scroll/order anti-patterns in AGENTS.md so future changes avoid the same classes of regressions.

packages/ui/src/components/views/PierreDiffViewer.tsx

@@ -24,7 +24,6 @@ import { useWorkerPool } from '@/contexts/DiffWorkerProvider';
 import { ensurePierreThemeRegistered, getResolvedShikiTheme } from '@/lib/shiki/appThemeRegistry';
 import { getDefaultTheme } from '@/lib/theme/themes';
 
-import { useUIStore } from '@/stores/useUIStore';
 import { useDeviceInfo } from '@/lib/device';
 import { cn } from '@/lib/utils';
 
@@ -209,7 +208,6 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
   const lightTheme = themeContext?.availableThemes.find(t => t.metadata.id === themeContext.lightThemeId) ?? getDefaultTheme(false);
   const darkTheme = themeContext?.availableThemes.find(t => t.metadata.id === themeContext.darkThemeId) ?? getDefaultTheme(true);
 
-  useUIStore();
   const { isMobile } = useDeviceInfo();
 
   const diffCommentController = useInlineCommentController<SelectedLineRange>({

packages/ui/src/components/views/PlanView.tsx

@@ -5,7 +5,6 @@ import { SimpleMarkdownRenderer } from '@/components/chat/MarkdownRenderer';
 import { ErrorBoundary } from '@/components/ui/ErrorBoundary';
 import { ScrollableOverlay } from '@/components/ui/ScrollableOverlay';
 import { Button } from '@/components/ui/button';
-import { useUIStore } from '@/stores/useUIStore';
 import { buildCodeMirrorCommentWidgets, normalizeLineRange, useInlineCommentController } from '@/components/comments';
 
 import { getLanguageFromExtension } from '@/lib/toolHelpers';
@@ -87,7 +86,6 @@ export const PlanView: React.FC = () => {
   const homeDirectory = useDirectoryStore((state) => state.homeDirectory);
   const planModeEnabled = useFeatureFlagsStore((state) => state.planModeEnabled);
   const runtimeApis = useRuntimeAPIs();
-  useUIStore();
   const { isMobile } = useDeviceInfo();
   const { currentTheme } = useThemeSystem();
   React.useMemo(() => generateSyntaxTheme(currentTheme), [currentTheme]);