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/hooks/useEffectiveDirectory.ts

@@ -1,7 +1,6 @@
 import { useSessionUIStore } from '@/sync/session-ui-store';
-import { useSessions } from '@/sync/sync-context';
+import { useSessionDirectory } from '@/sync/sync-context';
 import { useDirectoryStore } from '@/stores/useDirectoryStore';
-import type { Session } from '@opencode-ai/sdk/v2';
 
 /**
  * Hook that resolves the effective working directory for tabs (Git, Diff, Files, Terminal).
@@ -18,7 +17,7 @@ import type { Session } from '@opencode-ai/sdk/v2';
 export const useEffectiveDirectory = (): string | undefined => {
     const currentSessionId = useSessionUIStore((s) => s.currentSessionId);
     const newSessionDraft = useSessionUIStore((s) => s.newSessionDraft);
-    const sessions = useSessions();
+    const currentSessionDirectory = useSessionDirectory(currentSessionId);
     const worktreeMap = useSessionUIStore((s) => s.worktreeMetadata);
     const fallbackDirectory = useDirectoryStore((s) => s.currentDirectory);
 
@@ -28,12 +27,8 @@ export const useEffectiveDirectory = (): string | undefined => {
         if (worktreeMetadata?.path) {
             return worktreeMetadata.path;
         }
-
-        const currentSession = sessions.find((session) => session.id === currentSessionId);
-        type SessionWithDirectory = Session & { directory?: string };
-        const sessionDirectory = (currentSession as SessionWithDirectory | undefined)?.directory;
-        if (sessionDirectory) {
-            return sessionDirectory;
+        if (currentSessionDirectory) {
+            return currentSessionDirectory;
         }
     }