diff --git a/packages/app/src/composables/useCleanup.ts b/packages/app/src/composables/useCleanup.ts
new file mode 100644
index 00000000..6eaccf70
--- /dev/null
+++ b/packages/app/src/composables/useCleanup.ts
@@ -0,0 +1,51 @@
+import { onUnmounted } from 'vue'
+
+/**
+ * Memory leak prevention composable.
+ * Tracks intervals, timeouts, listeners, and observers
+ * for automatic cleanup on component unmount.
+ */
+export function useCleanup() {
+  const intervals: ReturnType<typeof setInterval>[] = []
+  const timeouts: ReturnType<typeof setTimeout>[] = []
+  const listeners: { target: EventTarget; event: string; handler: EventListenerOrEventListenerObject }[] = []
+  const observers: { disconnect: () => void }[] = []
+
+  function addInterval(fn: () => void, ms: number): ReturnType<typeof setInterval> {
+    const id = setInterval(fn, ms)
+    intervals.push(id)
+    return id
+  }
+
+  function addTimeout(fn: () => void, ms: number): ReturnType<typeof setTimeout> {
+    const id = setTimeout(fn, ms)
+    timeouts.push(id)
+    return id
+  }
+
+  function addListener(target: EventTarget, event: string, handler: EventListenerOrEventListenerObject, options?: AddEventListenerOptions) {
+    target.addEventListener(event, handler, options)
+    listeners.push({ target, event, handler })
+  }
+
+  function addObserver(observer: { disconnect: () => void }) {
+    observers.push(observer)
+    return observer
+  }
+
+  onUnmounted(() => {
+    for (const id of intervals) clearInterval(id)
+    for (const id of timeouts) clearTimeout(id)
+    for (const { target, event, handler } of listeners) {
+      target.removeEventListener(event, handler)
+    }
+    for (const obs of observers) obs.disconnect()
+  })
+
+  return {
+    addInterval,
+    addTimeout,
+    addListener,
+    addObserver,
+  }
+}
diff --git a/packages/app/src/composables/useDeduplicatedFetch.ts b/packages/app/src/composables/useDeduplicatedFetch.ts
new file mode 100644
index 00000000..6444082d
--- /dev/null
+++ b/packages/app/src/composables/useDeduplicatedFetch.ts
@@ -0,0 +1,29 @@
+const inflight = new Map<string, Promise<Response>>()
+
+export function useDeduplicatedFetch() {
+  async function dedupFetch(url: string, options?: RequestInit): Promise<Response> {
+    // Generate a cache key from URL + body
+    const bodyStr = options?.body ? String(options.body) : ''
+    const key = `${options?.method ?? 'GET'}:${url}:${bodyStr}`
+
+    const existing = inflight.get(key)
+    if (existing) return existing.then(r => r.clone())
+
+    const controller = new AbortController()
+    const mergedOptions = { ...options, signal: controller.signal }
+
+    const promise = fetch(url, mergedOptions).finally(() => {
+      inflight.delete(key)
+    })
+
+    inflight.set(key, promise)
+
+    return promise
+  }
+
+  function cancelAll() {
+    inflight.clear()
+  }
+
+  return { dedupFetch, cancelAll }
+}
diff --git a/packages/app/src/composables/useLazyImage.ts b/packages/app/src/composables/useLazyImage.ts
new file mode 100644
index 00000000..4c7b70f6
--- /dev/null
+++ b/packages/app/src/composables/useLazyImage.ts
@@ -0,0 +1,40 @@
+import { ref, onMounted, onUnmounted, type Ref } from 'vue'
+
+const PLACEHOLDER = 'data:image/svg+xml;base64,PHN2ZyB3aWR0aD0iMTYiIGhlaWdodD0iMTYiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyI+PHJlY3Qgd2lkdGg9IjE2IiBoZWlnaHQ9IjE2IiBmaWxsPSIjMWExYTFhIi8+PC9zdmc+'
+
+export function useLazyImage(imageRef: Ref<HTMLImageElement | null>, src: string) {
+  const isLoaded = ref(false)
+  const currentSrc = ref(PLACEHOLDER)
+  let observer: IntersectionObserver | null = null
+
+  function onLoad() {
+    isLoaded.value = true
+  }
+
+  onMounted(() => {
+    const el = imageRef.value
+    if (!el) return
+
+    observer = new IntersectionObserver(
+      (entries) => {
+        for (const entry of entries) {
+          if (entry.isIntersecting) {
+            currentSrc.value = src
+            el.src = src
+            el.addEventListener('load', onLoad, { once: true })
+            observer?.disconnect()
+          }
+        }
+      },
+      { rootMargin: '200px' }
+    )
+
+    observer.observe(el)
+  })
+
+  onUnmounted(() => {
+    observer?.disconnect()
+  })
+
+  return { isLoaded, currentSrc, placeholder: PLACEHOLDER }
+}
diff --git a/packages/app/src/composables/usePrefetch.ts b/packages/app/src/composables/usePrefetch.ts
new file mode 100644
index 00000000..3adef00e
--- /dev/null
+++ b/packages/app/src/composables/usePrefetch.ts
@@ -0,0 +1,32 @@
+const prefetchCache = new Map<string, { data: unknown; expiresAt: number }>()
+const CACHE_DURATION = 5 * 60 * 1000 // 5 minutes
+
+export function usePrefetch() {
+  function getCached<T>(key: string): T | null {
+    const entry = prefetchCache.get(key)
+    if (!entry) return null
+    if (Date.now() > entry.expiresAt) {
+      prefetchCache.delete(key)
+      return null
+    }
+    return entry.data as T
+  }
+
+  function setCached(key: string, data: unknown) {
+    prefetchCache.set(key, { data, expiresAt: Date.now() + CACHE_DURATION })
+  }
+
+  async function prefetch(key: string, fetcher: () => Promise<unknown>) {
+    if (getCached(key)) return
+    try {
+      const data = await fetcher()
+      setCached(key, data)
+    } catch { /* ignore prefetch errors */ }
+  }
+
+  function clearCache() {
+    prefetchCache.clear()
+  }
+
+  return { getCached, setCached, prefetch, clearCache }
+}
diff --git a/packages/app/src/composables/useSyncQueue.ts b/packages/app/src/composables/useSyncQueue.ts
new file mode 100644
index 00000000..02e3679d
--- /dev/null
+++ b/packages/app/src/composables/useSyncQueue.ts
@@ -0,0 +1,90 @@
+import { ref, onMounted, onUnmounted } from 'vue'
+
+const STORAGE_KEY = 'aiui-sync-queue'
+
+interface QueuedOperation {
+  id: string
+  type: string
+  data: unknown
+  createdAt: number
+}
+
+const queue = ref<QueuedOperation[]>([])
+const hasQueuedItems = ref(false)
+
+function loadQueue() {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY)
+    if (stored) queue.value = JSON.parse(stored)
+    hasQueuedItems.value = queue.value.length > 0
+  } catch { /* ignore */ }
+}
+
+function saveQueue() {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(queue.value))
+  hasQueuedItems.value = queue.value.length > 0
+}
+
+loadQueue()
+
+export function useSyncQueue() {
+  function enqueue(type: string, data: unknown) {
+    queue.value.push({
+      id: crypto.randomUUID(),
+      type,
+      data,
+      createdAt: Date.now(),
+    })
+    saveQueue()
+  }
+
+  async function processQueue(handler: (op: QueuedOperation) => Promise<boolean>) {
+    const remaining: QueuedOperation[] = []
+    for (const op of queue.value) {
+      try {
+        const success = await handler(op)
+        if (!success) remaining.push(op)
+      } catch {
+        remaining.push(op)
+      }
+    }
+    queue.value = remaining
+    saveQueue()
+  }
+
+  function clearQueue() {
+    queue.value = []
+    saveQueue()
+  }
+
+  // Auto-retry on visibility change
+  let retryHandler: (() => void) | null = null
+
+  function startAutoRetry(handler: (op: QueuedOperation) => Promise<boolean>) {
+    retryHandler = () => {
+      if (document.visibilityState === 'visible' && queue.value.length > 0) {
+        processQueue(handler)
+      }
+    }
+    document.addEventListener('visibilitychange', retryHandler)
+  }
+
+  onMounted(() => {
+    // Already loaded
+  })
+
+  onUnmounted(() => {
+    if (retryHandler) {
+      document.removeEventListener('visibilitychange', retryHandler)
+    }
+  })
+
+  return {
+    queue,
+    hasQueuedItems,
+    enqueue,
+    processQueue,
+    clearQueue,
+    startAutoRetry,
+  }
+}