fix(code): use stable empty references in session selector hooks

Zustand selectors use === to decide whether to re-render subscribers.
Returning `new Map()` or `[]` on every call creates a fresh reference
each time, causing every subscriber to re-render on every store update
even when nothing relevant changed. This matters during agent streaming
where the session store updates on every event.

Author: Twixes

apps/code/src/renderer/features/sessions/hooks/useSession.ts

@@ -16,6 +16,13 @@ import {
 } from "../stores/sessionStore";
 import type { PermissionRequest } from "../utils/parseSessionLogs";
 
+// Stable references for fallback values — returning the same object on every
+// call prevents Zustand's === check from triggering spurious re-renders.
+const EMPTY_MAP = new Map<string, PermissionRequest>();
+const EMPTY_COMMANDS: AvailableCommand[] = [];
+const EMPTY_QUEUE: QueuedMessage[] = [];
+const EMPTY_OPTIMISTIC: OptimisticItem[] = [];
+
 export const useSessions = () => useSessionStore((s) => s.sessions);
 
 /** O(1) lookup using taskIdIndex */
@@ -33,11 +40,11 @@ export const useAvailableCommandsForTask = (
   taskId: string | undefined,
 ): AvailableCommand[] => {
   return useSessionStore((s) => {
-    if (!taskId) return [];
+    if (!taskId) return EMPTY_COMMANDS;
     const taskRunId = s.taskIdIndex[taskId];
-    if (!taskRunId) return [];
+    if (!taskRunId) return EMPTY_COMMANDS;
     const session = s.sessions[taskRunId];
-    if (!session?.events) return [];
+    if (!session?.events) return EMPTY_COMMANDS;
     return extractAvailableCommandsFromEvents(session.events);
   });
 };
@@ -68,11 +75,11 @@ export const usePendingPermissionsForTask = (
   taskId: string | undefined,
 ): Map<string, PermissionRequest> => {
   return useSessionStore((s) => {
-    if (!taskId) return new Map();
+    if (!taskId) return EMPTY_MAP;
     const taskRunId = s.taskIdIndex[taskId];
-    if (!taskRunId) return new Map();
+    if (!taskRunId) return EMPTY_MAP;
     const session = s.sessions[taskRunId];
-    return session?.pendingPermissions ?? new Map();
+    return session?.pendingPermissions ?? EMPTY_MAP;
   });
 };
 
@@ -91,22 +98,22 @@ export const useQueuedMessagesForTask = (
   taskId: string | undefined,
 ): QueuedMessage[] => {
   return useSessionStore((s) => {
-    if (!taskId) return [];
+    if (!taskId) return EMPTY_QUEUE;
     const taskRunId = s.taskIdIndex[taskId];
-    if (!taskRunId) return [];
+    if (!taskRunId) return EMPTY_QUEUE;
     const session = s.sessions[taskRunId];
-    return session?.messageQueue ?? [];
+    return session?.messageQueue ?? EMPTY_QUEUE;
   });
 };
 
 export const useOptimisticItemsForTask = (
   taskId: string | undefined,
 ): OptimisticItem[] => {
   return useSessionStore((s) => {
-    if (!taskId) return [];
+    if (!taskId) return EMPTY_OPTIMISTIC;
     const taskRunId = s.taskIdIndex[taskId];
-    if (!taskRunId) return [];
-    return s.sessions[taskRunId]?.optimisticItems ?? [];
+    if (!taskRunId) return EMPTY_OPTIMISTIC;
+    return s.sessions[taskRunId]?.optimisticItems ?? EMPTY_OPTIMISTIC;
   });
 };