perf(renderer): convert the four lazy-useRef sites that landed on main

src/renderer/src/components/activity/use-agent-pane-threads.ts

@@ -121,8 +121,10 @@ export function useAgentPaneThreads(args: {
   // identities across rebuilds, so a status write to one agent leaves every other row's
   // memo bail-out and cached search text intact. Rebuilds are deterministic, so a repeated
   // (StrictMode/deferred) memo invocation returns identical objects from the cache.
-  const eventBuildCacheRef = useRef(createActivityEventBuildCache())
-  const threadReuseCacheRef = useRef(createAgentPaneThreadReuseCache())
+  const eventBuildCacheRef = useRef<ReturnType<typeof createActivityEventBuildCache>>(undefined!)
+  eventBuildCacheRef.current ??= createActivityEventBuildCache()
+  const threadReuseCacheRef = useRef<ReturnType<typeof createAgentPaneThreadReuseCache>>(undefined!)
+  threadReuseCacheRef.current ??= createAgentPaneThreadReuseCache()
 
   const { events: allEvents, liveAgentByPaneKey } = useMemo(
     () =>

src/renderer/src/components/dashboard/useAgentBucketCounts.ts

@@ -51,7 +51,8 @@ export function useAgentBucketCounts(): AgentBucketCounts {
 
   // Why a per-hook cache: unrelated status/title writes change one worktree's inputs;
   // the cache keeps every other worktree's counts without rerunning its row pipeline.
-  const cacheRef = useRef(createDashboardBucketCountsCache())
+  const cacheRef = useRef<ReturnType<typeof createDashboardBucketCountsCache>>(undefined!)
+  cacheRef.current ??= createDashboardBucketCountsCache()
   return useMemo(() => {
     return buildDashboardBucketCounts(
       {

src/renderer/src/components/dashboard/useLiveDashboardSnapshot.ts

@@ -11,7 +11,8 @@ import { createWorktreeAgentRowsCache } from './worktree-agent-rows-cache'
  * is no relay, so we derive it here from the same builder the bridge uses.
  */
 export function useLiveDashboardSnapshot(): DashboardSnapshot {
-  const rowsCacheRef = useRef(createWorktreeAgentRowsCache())
+  const rowsCacheRef = useRef<ReturnType<typeof createWorktreeAgentRowsCache>>(undefined!)
+  rowsCacheRef.current ??= createWorktreeAgentRowsCache()
   const repos = useAppStore((s) => s.repos)
   const worktreesByRepo = useAppStore((s) => s.worktreesByRepo)
   const tabsByWorktree = useAppStore((s) => s.tabsByWorktree)