diff --git a/src/agentkit/quality/cascade_state_store.py b/src/agentkit/quality/cascade_state_store.py
index b4a2e70..5e3e8b3 100644
--- a/src/agentkit/quality/cascade_state_store.py
+++ b/src/agentkit/quality/cascade_state_store.py
@@ -241,5 +241,4 @@ def create_cascade_state_store(
             return RedisCascadeStateStore(redis_url=redis_url, session_ttl=session_ttl)
         except ImportError:
             logger.warning("redis package not available, falling back to in-memory cascade store")
-            return InMemoryCascadeStateStore()
-    return InMemoryCascadeStateStore()
+    return InMemoryCascadeStateStore(session_ttl=session_ttl)
diff --git a/src/agentkit/server/frontend/src/App.vue b/src/agentkit/server/frontend/src/App.vue
index c5ca2c2..bf3365d 100644
--- a/src/agentkit/server/frontend/src/App.vue
+++ b/src/agentkit/server/frontend/src/App.vue
@@ -1,5 +1,5 @@
 <template>
-  <a-config-provider :locale="zhCN" :theme="themeConfig">
+  <a-config-provider :locale="zhCN" :theme="themeStore.antThemeConfig.value">
     <SplashScreen v-if="loading" :status="loadingStatus" :error="loadError" />
     <router-view v-else />
   </a-config-provider>
@@ -9,11 +9,13 @@
 import { ref, onMounted } from 'vue'
 import { ConfigProvider as AConfigProvider } from 'ant-design-vue'
 import zhCN from 'ant-design-vue/es/locale/zh_CN'
-import { themeConfig } from './styles'
+import { useThemeStore } from './stores/theme'
 import { isTauri, startBackend, checkBackendHealth } from './api/tauri'
 import { initApiBaseURL } from './api/base'
 import SplashScreen from './components/layout/SplashScreen.vue'
 
+const themeStore = useThemeStore()
+
 const loading = ref(isTauri())
 const loadingStatus = ref('正在初始化...')
 const loadError = ref('')
diff --git a/src/agentkit/server/frontend/src/components/chat/ChatInput.vue b/src/agentkit/server/frontend/src/components/chat/ChatInput.vue
index 435906c..d57bdb6 100644
--- a/src/agentkit/server/frontend/src/components/chat/ChatInput.vue
+++ b/src/agentkit/server/frontend/src/components/chat/ChatInput.vue
@@ -1,5 +1,5 @@
 <template>
-  <div class="chat-input">
+  <div class="chat-input" style="position: relative;">
     <div v-if="contextPills.length > 0" class="chat-input__pills">
       <ContextPill
         v-for="(pill, idx) in contextPills"
@@ -10,13 +10,23 @@
         @remove="removePill(idx)"
       />
     </div>
+    <MentionDropdown
+      :visible="mentionVisible"
+      :query="mentionQuery"
+      :skills="skillSuggestions"
+      :position="mentionPosition"
+      @select="insertMention"
+      @close="closeMention"
+    />
     <div class="chat-input__row">
       <a-textarea
+        ref="textareaRef"
         v-model:value="inputText"
         :placeholder="placeholder"
         :auto-size="{ minRows: 1, maxRows: 4 }"
         :disabled="disabled"
         @pressEnter="handlePressEnter"
+        @input="handleInput"
         class="chat-input__textarea"
       />
       <a-button
@@ -37,6 +47,8 @@ import { ref, computed, type Component } from 'vue'
 import { Input as AInput, Button as AButton } from 'ant-design-vue'
 import { SendOutlined } from '@ant-design/icons-vue'
 import ContextPill from './ContextPill.vue'
+import MentionDropdown from './MentionDropdown.vue'
+import { useSkillsStore } from '@/stores/skills'
 
 const ATextarea = AInput.TextArea
 
@@ -46,6 +58,11 @@ interface ContextPillData {
   removable?: boolean
 }
 
+interface SkillSuggestion {
+  name: string
+  description: string
+}
+
 interface IProps {
   disabled?: boolean
   placeholder?: string
@@ -62,19 +79,86 @@ const emit = defineEmits<{
 
 const inputText = ref('')
 const contextPills = ref<ContextPillData[]>([])
+const textareaRef = ref<InstanceType<typeof ATextarea> | null>(null)
+
+// @-mention state
+const mentionVisible = ref(false)
+const mentionQuery = ref('')
+const mentionStartIndex = ref(-1)
+const mentionPosition = ref({ left: 0 })
+const skillsStore = useSkillsStore()
+
+const skillSuggestions = computed<SkillSuggestion[]>(() => {
+  return (skillsStore.skills || []).map((s: any) => ({
+    name: s.name,
+    description: s.description || '',
+  }))
+})
 
 const canSend = computed(() => {
   return inputText.value.trim().length > 0 && !props.disabled
 })
 
+function handleInput(): void {
+  detectMention()
+}
+
+function detectMention(): void {
+  const text = inputText.value
+  const cursorPos = text.length  // textarea cursor at end for v-model
+
+  // Find the last @ that starts a potential mention
+  const lastAtIndex = text.lastIndexOf('@', cursorPos)
+  if (lastAtIndex === -1) {
+    closeMention()
+    return
+  }
+
+  // Check if there's a space between @ and cursor (mention is complete)
+  const textAfterAt = text.slice(lastAtIndex + 1, cursorPos)
+  if (textAfterAt.includes(' ') || textAfterAt.includes('\n')) {
+    closeMention()
+    return
+  }
+
+  // Check if @ is at start or preceded by whitespace
+  if (lastAtIndex > 0 && !/\s/.test(text[lastAtIndex - 1])) {
+    closeMention()
+    return
+  }
+
+  mentionVisible.value = true
+  mentionQuery.value = textAfterAt
+  mentionStartIndex.value = lastAtIndex
+
+  // Estimate horizontal position based on character count
+  mentionPosition.value = { left: Math.min(lastAtIndex * 8, 200) }
+}
+
+function insertMention(skill: SkillSuggestion): void {
+  const text = inputText.value
+  const before = text.slice(0, mentionStartIndex.value)
+  const after = text.slice(mentionStartIndex.value + 1 + mentionQuery.value.length)
+  inputText.value = `${before}@${skill.name} ${after}`
+  closeMention()
+}
+
+function closeMention(): void {
+  mentionVisible.value = false
+  mentionQuery.value = ''
+  mentionStartIndex.value = -1
+}
+
 function handleSend(): void {
   const message = inputText.value.trim()
   if (!message) return
+  closeMention()
   emit('send', message)
-  inputText.value = ''
+  setTimeout(() => { inputText.value = '' }, 0)
 }
 
 function handlePressEnter(event: KeyboardEvent): void {
+  if (mentionVisible.value) return  // Let MentionDropdown handle Enter
   if (event.shiftKey) return
   event.preventDefault()
   handleSend()
@@ -89,9 +173,9 @@ function removePill(idx: number): void {
 .chat-input {
   display: flex;
   flex-direction: column;
-  padding: var(--space-2) var(--space-3);
+  padding: var(--space-3) var(--space-4);
   background: var(--bg-primary);
-  border-top: 1px solid var(--border-color);
+  border-top: 1px solid var(--border-color-split);
 }
 
 .chat-input__pills {
@@ -105,6 +189,16 @@ function removePill(idx: number): void {
   display: flex;
   align-items: flex-end;
   gap: var(--space-2);
+  background: var(--bg-primary);
+  border-radius: var(--radius-lg);
+  padding: var(--space-1) var(--space-2);
+  border: 1px solid var(--border-color);
+  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
+}
+
+.chat-input__row:focus-within {
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 3px var(--color-primary-light);
 }
 
 .chat-input__textarea {
@@ -117,11 +211,34 @@ function removePill(idx: number): void {
   line-height: 1.5;
   padding-top: 8px;
   padding-bottom: 8px;
+  background: transparent;
+  border: none;
+  box-shadow: none !important;
+  font-size: var(--font-base);
+}
+
+.chat-input__textarea :deep(.ant-input:focus) {
+  box-shadow: none !important;
+}
+
+.chat-input__textarea :deep(.ant-input::placeholder) {
+  color: var(--text-placeholder);
 }
 
 .chat-input__send {
   flex-shrink: 0;
   height: 40px;
   min-height: 40px;
+  border-radius: var(--radius-md) !important;
+  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
+}
+
+.chat-input__send:not(:disabled):hover {
+  transform: translateY(-1px);
+  box-shadow: 0 2px 8px rgba(99, 102, 241, 0.3);
+}
+
+.chat-input__send:not(:disabled):active {
+  transform: translateY(0);
 }
 </style>
diff --git a/src/agentkit/server/frontend/src/components/chat/MentionDropdown.vue b/src/agentkit/server/frontend/src/components/chat/MentionDropdown.vue
new file mode 100644
index 0000000..3af784b
--- /dev/null
+++ b/src/agentkit/server/frontend/src/components/chat/MentionDropdown.vue
@@ -0,0 +1,168 @@
+<template>
+  <div v-if="visible && filteredSkills.length > 0" class="mention-dropdown" :style="positionStyle">
+    <div class="mention-dropdown__header">
+      <span class="mention-dropdown__title">技能</span>
+      <span class="mention-dropdown__hint">选择或继续输入筛选</span>
+    </div>
+    <div class="mention-dropdown__list">
+      <button
+        v-for="(skill, idx) in filteredSkills"
+        :key="skill.name"
+        class="mention-dropdown__item"
+        :class="{ 'mention-dropdown__item--active': idx === activeIndex }"
+        @click="selectSkill(skill)"
+        @mouseenter="activeIndex = idx"
+      >
+        <span class="mention-dropdown__item-name">{{ skill.name }}</span>
+        <span class="mention-dropdown__item-desc">{{ skill.description }}</span>
+      </button>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed, watch, onMounted, onUnmounted } from 'vue'
+
+interface SkillSuggestion {
+  name: string
+  description: string
+}
+
+interface IProps {
+  visible: boolean
+  query: string
+  skills: SkillSuggestion[]
+  position?: { top: number; left: number }
+}
+
+const props = withDefaults(defineProps<IProps>(), {
+  position: () => ({ top: 0, left: 0 }),
+})
+
+const emit = defineEmits<{
+  select: [skill: SkillSuggestion]
+  close: []
+}>()
+
+const activeIndex = ref(0)
+
+const filteredSkills = computed(() => {
+  const q = props.query.toLowerCase()
+  if (!q) return props.skills.slice(0, 8)
+  return props.skills
+    .filter(s => s.name.toLowerCase().includes(q) || s.description.toLowerCase().includes(q))
+    .slice(0, 8)
+})
+
+const positionStyle = computed(() => ({
+  position: 'absolute' as const,
+  bottom: `calc(100% + 4px)`,
+  left: `${props.position.left}px`,
+}))
+
+watch(() => props.query, () => {
+  activeIndex.value = 0
+})
+
+function selectSkill(skill: SkillSuggestion) {
+  emit('select', skill)
+}
+
+function handleKeyDown(e: KeyboardEvent) {
+  if (!props.visible || filteredSkills.value.length === 0) return
+
+  if (e.key === 'ArrowDown') {
+    e.preventDefault()
+    activeIndex.value = (activeIndex.value + 1) % filteredSkills.value.length
+  } else if (e.key === 'ArrowUp') {
+    e.preventDefault()
+    activeIndex.value = (activeIndex.value - 1 + filteredSkills.value.length) % filteredSkills.value.length
+  } else if (e.key === 'Enter' && !e.shiftKey) {
+    e.preventDefault()
+    selectSkill(filteredSkills.value[activeIndex.value])
+  } else if (e.key === 'Escape') {
+    e.preventDefault()
+    emit('close')
+  }
+}
+
+onMounted(() => {
+  document.addEventListener('keydown', handleKeyDown)
+})
+
+onUnmounted(() => {
+  document.removeEventListener('keydown', handleKeyDown)
+})
+</script>
+
+<style scoped>
+.mention-dropdown {
+  background: var(--bg-elevated);
+  border: 1px solid var(--border-color);
+  border-radius: var(--radius-lg);
+  box-shadow: var(--shadow-lg);
+  min-width: 280px;
+  max-width: 400px;
+  z-index: var(--z-dropdown);
+  overflow: hidden;
+}
+
+.mention-dropdown__header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--space-2) var(--space-3);
+  border-bottom: 1px solid var(--border-color-split);
+}
+
+.mention-dropdown__title {
+  font-size: var(--font-xs);
+  font-weight: var(--font-weight-semibold);
+  color: var(--text-tertiary);
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.mention-dropdown__hint {
+  font-size: var(--font-xs);
+  color: var(--text-placeholder);
+}
+
+.mention-dropdown__list {
+  max-height: 240px;
+  overflow-y: auto;
+  padding: var(--space-1) 0;
+}
+
+.mention-dropdown__item {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  width: 100%;
+  padding: var(--space-2) var(--space-3);
+  border: none;
+  background: transparent;
+  cursor: pointer;
+  text-align: left;
+  transition: background var(--transition-fast);
+}
+
+.mention-dropdown__item:hover,
+.mention-dropdown__item--active {
+  background: var(--bg-tertiary);
+}
+
+.mention-dropdown__item-name {
+  font-size: var(--font-sm);
+  font-weight: var(--font-weight-medium);
+  color: var(--text-primary);
+}
+
+.mention-dropdown__item-desc {
+  font-size: var(--font-xs);
+  color: var(--text-tertiary);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+</style>
diff --git a/src/agentkit/server/frontend/src/components/layout/TopNav.vue b/src/agentkit/server/frontend/src/components/layout/TopNav.vue
index 61a5a99..a0a5bbf 100644
--- a/src/agentkit/server/frontend/src/components/layout/TopNav.vue
+++ b/src/agentkit/server/frontend/src/components/layout/TopNav.vue
@@ -1,6 +1,10 @@
 <template>
   <header class="top-nav">
     <div class="top-nav__left">
+      <button class="top-nav__icon-btn" @click="emit('toggleIconNav')" title="切换导航">
+        <MenuFoldOutlined v-if="!iconNavCollapsed" />
+        <MenuUnfoldOutlined v-else />
+      </button>
       <div class="top-nav__logo" @click="router.push('/agent')">
         <span class="top-nav__logo-text">Fischer</span>
         <span class="top-nav__logo-badge">AgentKit</span>
@@ -17,6 +21,12 @@
           :text="wsConnected ? '已连接' : '未连接'"
         />
       </div>
+      <a-tooltip :title="isDark ? '切换亮色模式' : '切换暗色模式'">
+        <button class="top-nav__icon-btn" @click="themeStore.toggle()">
+          <BulbOutlined v-if="isDark" />
+          <BulbOutlined v-else style="opacity: 0.5" />
+        </button>
+      </a-tooltip>
       <a-tooltip title="设置">
         <button class="top-nav__icon-btn" @click="router.push('/agent/monitor?tab=settings')">
           <SettingOutlined />
@@ -30,12 +40,24 @@
 import { computed } from 'vue'
 import { useRouter } from 'vue-router'
 import { Badge as ABadge, Tooltip as ATooltip } from 'ant-design-vue'
-import { SettingOutlined } from '@ant-design/icons-vue'
+import { SettingOutlined, MenuFoldOutlined, MenuUnfoldOutlined, BulbOutlined } from '@ant-design/icons-vue'
 import { useChatStore } from '@/stores/chat'
+import { useThemeStore } from '@/stores/theme'
+
+const props = defineProps<{
+  iconNavCollapsed?: boolean
+}>()
+
+const emit = defineEmits<{
+  toggleIconNav: []
+}>()
 
 const router = useRouter()
 const chatStore = useChatStore()
+const themeStore = useThemeStore()
 const wsConnected = computed(() => chatStore.isWsConnected)
+const iconNavCollapsed = computed(() => props.iconNavCollapsed ?? false)
+const isDark = computed(() => themeStore.resolvedMode === 'dark')
 </script>
 
 <style scoped>
@@ -44,11 +66,11 @@ const wsConnected = computed(() => chatStore.isWsConnected)
   align-items: center;
   justify-content: space-between;
   height: var(--topnav-height);
-  padding: 0 var(--space-4);
+  padding: 0 var(--space-5);
   background: var(--bg-primary);
-  border-bottom: 1px solid var(--border-color);
+  border-bottom: 1px solid var(--border-color-split);
   flex-shrink: 0;
-  z-index: var(--z-sticky);
+  z-index: 100;
 }
 
 .top-nav__left {
@@ -63,6 +85,13 @@ const wsConnected = computed(() => chatStore.isWsConnected)
   gap: var(--space-2);
   cursor: pointer;
   user-select: none;
+  padding: var(--space-1) var(--space-2);
+  border-radius: var(--radius-md);
+  transition: background var(--transition-fast);
+}
+
+.top-nav__logo:hover {
+  background: var(--bg-tertiary);
 }
 
 .top-nav__logo-text {
@@ -79,9 +108,9 @@ const wsConnected = computed(() => chatStore.isWsConnected)
   font-weight: var(--font-weight-medium);
   color: var(--text-inverse);
   background: var(--gradient-brand);
-  padding: 1px var(--space-2);
+  padding: 2px var(--space-2);
   border-radius: var(--radius-full);
-  letter-spacing: 0.5px;
+  letter-spacing: 0.3px;
 }
 
 .top-nav__center {
@@ -96,11 +125,14 @@ const wsConnected = computed(() => chatStore.isWsConnected)
 .top-nav__right {
   display: flex;
   align-items: center;
-  gap: var(--space-3);
+  gap: var(--space-2);
 }
 
 .top-nav__status {
   font-size: var(--font-xs);
+  padding: var(--space-1) var(--space-2);
+  border-radius: var(--radius-full);
+  background: var(--bg-tertiary);
 }
 
 .top-nav__status :deep(.ant-badge-status-text) {
@@ -112,8 +144,8 @@ const wsConnected = computed(() => chatStore.isWsConnected)
   display: flex;
   align-items: center;
   justify-content: center;
-  width: 32px;
-  height: 32px;
+  width: 34px;
+  height: 34px;
   border: none;
   background: transparent;
   color: var(--text-tertiary);
diff --git a/src/agentkit/server/frontend/src/stores/theme.ts b/src/agentkit/server/frontend/src/stores/theme.ts
new file mode 100644
index 0000000..378c94d
--- /dev/null
+++ b/src/agentkit/server/frontend/src/stores/theme.ts
@@ -0,0 +1,143 @@
+/**
+ * Theme Store — Dark mode toggle with system preference detection.
+ *
+ * Persists preference to localStorage and syncs with the `data-theme`
+ * attribute on <html>. Also provides a reactive Ant Design theme config
+ * that updates when the mode changes.
+ */
+
+import { ref, computed, watchEffect } from 'vue'
+import { defineStore } from 'pinia'
+import type { ThemeConfig } from 'ant-design-vue/es/config-provider/context'
+
+export type ThemeMode = 'light' | 'dark' | 'system'
+
+const STORAGE_KEY = 'agentkit-theme-mode'
+
+function readToken(varName: string, fallback: string): string {
+  if (typeof document === 'undefined') return fallback
+  const val = getComputedStyle(document.documentElement).getPropertyValue(varName).trim()
+  return val || fallback
+}
+
+function getSystemPreference(): 'light' | 'dark' {
+  if (typeof window === 'undefined') return 'light'
+  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+}
+
+function getStoredMode(): ThemeMode {
+  if (typeof localStorage === 'undefined') return 'system'
+  return (localStorage.getItem(STORAGE_KEY) as ThemeMode) || 'system'
+}
+
+function applyTheme(resolved: 'light' | 'dark') {
+  if (typeof document === 'undefined') return
+  document.documentElement.setAttribute('data-theme', resolved)
+}
+
+export const useThemeStore = defineStore('theme', () => {
+  const mode = ref<ThemeMode>(getStoredMode())
+
+  const resolvedMode = computed<'light' | 'dark'>(() => {
+    if (mode.value === 'system') return getSystemPreference()
+    return mode.value
+  })
+
+  function setMode(newMode: ThemeMode) {
+    mode.value = newMode
+    localStorage.setItem(STORAGE_KEY, newMode)
+  }
+
+  function toggle() {
+    if (resolvedMode.value === 'light') {
+      setMode('dark')
+    } else {
+      setMode('light')
+    }
+  }
+
+  // Apply theme whenever resolvedMode changes
+  watchEffect(() => {
+    applyTheme(resolvedMode.value)
+  })
+
+  // Listen for system preference changes
+  if (typeof window !== 'undefined') {
+    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
+      // Force re-evaluation when system preference changes
+      if (mode.value === 'system') {
+        applyTheme(getSystemPreference())
+      }
+    })
+  }
+
+  // Ant Design Vue theme config — reactive to dark mode
+  const antThemeConfig = computed<ThemeConfig>(() => {
+    const isDark = resolvedMode.value === 'dark'
+
+    return {
+      algorithm: isDark ? undefined : undefined, // Ant Design 4.x uses token-based theming
+      token: {
+        colorPrimary: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+        colorInfo: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+        colorSuccess: readToken('--color-success', isDark ? '#4ade80' : '#22c55e'),
+        colorWarning: readToken('--color-warning', isDark ? '#fbbf24' : '#f59e0b'),
+        colorError: readToken('--color-error', isDark ? '#f87171' : '#ef4444'),
+        colorText: readToken('--text-primary', isDark ? '#fbfbfa' : '#1a1a1a'),
+        colorTextSecondary: readToken('--text-secondary', isDark ? '#cececd' : '#4a4a4a'),
+        colorTextTertiary: readToken('--text-tertiary', isDark ? '#9b9b9a' : '#6b6b6a'),
+        colorTextQuaternary: readToken('--text-placeholder', isDark ? '#6b6b6a' : '#9b9b9a'),
+        colorBgContainer: readToken('--bg-primary', isDark ? '#1a1a1a' : '#ffffff'),
+        colorBgLayout: readToken('--bg-secondary', isDark ? '#1f1f1f' : '#fbfbfa'),
+        colorBgElevated: readToken('--bg-elevated', isDark ? '#252525' : '#ffffff'),
+        colorBorder: readToken('--border-color', isDark ? '#3a3a3a' : '#ededec'),
+        colorBorderSecondary: readToken('--border-color-split', isDark ? '#2f2f2f' : '#f2f2f0'),
+        fontSize: 14,
+        fontSizeSM: 12,
+        fontSizeLG: 16,
+        fontSizeXL: 20,
+        borderRadius: 8,
+        borderRadiusSM: 6,
+        borderRadiusLG: 12,
+        controlHeight: 32,
+        controlHeightSM: 24,
+        controlHeightLG: 40,
+        boxShadow: isDark
+          ? '0 1px 2px rgba(0, 0, 0, 0.2)'
+          : '0 1px 2px rgba(0, 0, 0, 0.04)',
+        boxShadowSecondary: isDark
+          ? '0 2px 8px rgba(0, 0, 0, 0.25), 0 1px 2px rgba(0, 0, 0, 0.15)'
+          : '0 2px 8px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04)',
+      },
+      components: {
+        Menu: {
+          itemSelectedBg: readToken('--color-primary-light', isDark ? '#1e1b4b' : '#eef2ff'),
+          itemSelectedColor: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+          itemHoverBg: isDark ? '#1e1b4b' : '#f5f3ff',
+          itemHoverColor: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+          itemColor: readToken('--text-secondary', isDark ? '#cececd' : '#4a4a4a'),
+        } as Record<string, unknown>,
+        Tabs: {
+          itemSelectedColor: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+          itemHoverColor: readToken('--color-primary-hover', isDark ? '#6366f1' : '#4f46e5'),
+        } as Record<string, unknown>,
+        Select: {
+          colorPrimary: readToken('--color-primary', isDark ? '#818cf8' : '#6366f1'),
+          colorPrimaryHover: readToken('--color-primary-hover', isDark ? '#6366f1' : '#4f46e5'),
+        } as Record<string, unknown>,
+        Button: { borderRadius: 8, controlHeight: 32 } as Record<string, unknown>,
+        Card: { borderRadiusLG: 10 } as Record<string, unknown>,
+        Input: { borderRadius: 8 } as Record<string, unknown>,
+        Modal: { borderRadiusLG: 12 } as Record<string, unknown>,
+      },
+    }
+  })
+
+  return {
+    mode,
+    resolvedMode,
+    antThemeConfig,
+    setMode,
+    toggle,
+  }
+})
diff --git a/src/agentkit/server/frontend/src/styles/tokens.css b/src/agentkit/server/frontend/src/styles/tokens.css
index 3325388..90bec14 100644
--- a/src/agentkit/server/frontend/src/styles/tokens.css
+++ b/src/agentkit/server/frontend/src/styles/tokens.css
@@ -1,63 +1,70 @@
 /**
- * Fischer AgentKit Design Tokens
+ * Fischer AgentKit Design Tokens — Notion-Inspired Light Theme
  *
  * CSS Custom Properties as the single source of truth.
  * Ant Design Vue theme tokens are mapped from these values in theme.ts.
+ *
+ * Design Philosophy:
+ * - Warm neutrals (Notion-style) instead of cold grays
+ * - Softer shadows with more spread, less offset
+ * - Generous border-radius for friendly feel
+ * - Subtle borders that fade into background
+ * - Refined hover/active states with gentle transitions
  */
 
 :root {
   /* ── Brand Colors ── */
-  --color-primary: #7c3aed;
-  --color-primary-hover: #6d28d9;
-  --color-primary-active: #5b21b6;
-  --color-primary-light: #ede9fe;
+  --color-primary: #6366f1;
+  --color-primary-hover: #4f46e5;
+  --color-primary-active: #4338ca;
+  --color-primary-light: #eef2ff;
   --color-primary-bg: #f5f3ff;
 
   /* ── Gradient ── */
-  --gradient-brand: linear-gradient(135deg, #7c3aed 0%, #1e1b4b 100%);
+  --gradient-brand: linear-gradient(135deg, #6366f1 0%, #312e81 100%);
 
   /* ── Semantic Colors ── */
-  --color-success: #10b981;
-  --color-success-light: #d1fae5;
+  --color-success: #22c55e;
+  --color-success-light: #dcfce7;
   --color-warning: #f59e0b;
-  --color-warning-light: #fef3c7;
+  --color-warning-light: #fef9c3;
   --color-error: #ef4444;
   --color-error-light: #fee2e2;
   --color-info: #3b82f6;
   --color-info-light: #dbeafe;
 
-  /* ── Neutral / Gray Scale ── */
-  --color-gray-50: #fafafa;
-  --color-gray-100: #f5f5f5;
-  --color-gray-200: #e5e5e5;
-  --color-gray-300: #d4d4d4;
-  --color-gray-400: #a3a3a3;
-  --color-gray-500: #737373;
-  --color-gray-600: #525252;
-  --color-gray-700: #404040;
-  --color-gray-800: #262626;
-  --color-gray-900: #171717;
+  /* ── Neutral / Warm Gray Scale (Notion-inspired) ── */
+  --color-gray-50: #fbfbfa;
+  --color-gray-100: #f7f7f5;
+  --color-gray-200: #ededec;
+  --color-gray-300: #dfdfde;
+  --color-gray-400: #cececd;
+  --color-gray-500: #9b9b9a;
+  --color-gray-600: #6b6b6a;
+  --color-gray-700: #4a4a4a;
+  --color-gray-800: #2f2f2f;
+  --color-gray-900: #1a1a1a;
 
   /* ── Background ── */
   --bg-primary: #ffffff;
-  --bg-secondary: #fafafa;
-  --bg-tertiary: #f5f5f5;
+  --bg-secondary: #fbfbfa;
+  --bg-tertiary: #f7f7f5;
   --bg-elevated: #ffffff;
-  --bg-code: #282c34;
+  --bg-code: #1e1e2e;
 
   /* ── Foreground / Text ── */
-  --text-primary: #171717;
-  --text-secondary: #525252;
-  --text-tertiary: #737373;
-  --text-placeholder: #a3a3a3;
+  --text-primary: #1a1a1a;
+  --text-secondary: #4a4a4a;
+  --text-tertiary: #6b6b6a;
+  --text-placeholder: #9b9b9a;
   --text-inverse: #ffffff;
-  --text-code: #abb2bf;
+  --text-code: #cdd6f4;
 
   /* ── Border ── */
-  --border-color: #e5e5e5;
-  --border-color-hover: #d4d4d4;
+  --border-color: #ededec;
+  --border-color-hover: #dfdfde;
   --border-color-active: var(--color-primary);
-  --border-color-split: #f0f0f0;
+  --border-color-split: #f2f2f0;
 
   /* ── Spacing ── */
   --space-1: 4px;
@@ -73,8 +80,8 @@
   /* ── Border Radius ── */
   --radius-sm: 4px;
   --radius-md: 6px;
-  --radius-lg: 8px;
-  --radius-xl: 12px;
+  --radius-lg: 10px;
+  --radius-xl: 14px;
   --radius-full: 9999px;
 
   /* ── Font Size ── */
@@ -96,11 +103,11 @@
   --leading-normal: 1.5;
   --leading-relaxed: 1.75;
 
-  /* ── Shadow ── */
-  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
-  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
-  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
-  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.08), 0 8px 10px -6px rgba(0, 0, 0, 0.04);
+  /* ── Shadow (Notion-style: softer, more ambient) ── */
+  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
+  --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
+  --shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.06), 0 2px 4px rgba(0, 0, 0, 0.04);
+  --shadow-xl: 0 8px 32px rgba(0, 0, 0, 0.08), 0 2px 8px rgba(0, 0, 0, 0.04);
 
   /* ── Transition ── */
   --transition-fast: 150ms ease;
@@ -121,16 +128,91 @@
   --sidebar-width: 280px;
   --quadrant-min-size: 320px;
 
-  /* ── Code Theme (One Dark Pro) ── */
-  --code-bg: #282c34;
-  --code-fg: #abb2bf;
-  --code-keyword: #c678dd;
-  --code-string: #98c379;
-  --code-number: #d19a66;
-  --code-comment: #5c6370;
-  --code-function: #61afef;
-  --code-variable: #e06c75;
-  --code-type: #e5c07b;
-  --code-added-bg: rgba(16, 185, 129, 0.15);
-  --code-removed-bg: rgba(239, 68, 68, 0.15);
+  /* ── Code Theme (Catppuccin Mocha — warmer dark theme) ── */
+  --code-bg: #1e1e2e;
+  --code-fg: #cdd6f4;
+  --code-keyword: #cba6f7;
+  --code-string: #a6e3a1;
+  --code-number: #fab387;
+  --code-comment: #6c7086;
+  --code-function: #89b4fa;
+  --code-variable: #f38ba8;
+  --code-type: #f9e2af;
+  --code-added-bg: rgba(166, 227, 161, 0.15);
+  --code-removed-bg: rgba(243, 139, 168, 0.15);
+}
+
+/* ── Dark Theme ── */
+[data-theme="dark"] {
+  /* ── Brand Colors ── */
+  --color-primary: #818cf8;
+  --color-primary-hover: #6366f1;
+  --color-primary-active: #4f46e5;
+  --color-primary-light: #1e1b4b;
+  --color-primary-bg: #1e1b4b;
+
+  /* ── Gradient ── */
+  --gradient-brand: linear-gradient(135deg, #818cf8 0%, #4338ca 100%);
+
+  /* ── Semantic Colors ── */
+  --color-success: #4ade80;
+  --color-success-light: #14532d;
+  --color-warning: #fbbf24;
+  --color-warning-light: #422006;
+  --color-error: #f87171;
+  --color-error-light: #450a0a;
+  --color-info: #60a5fa;
+  --color-info-light: #172554;
+
+  /* ── Neutral / Warm Gray Scale (Dark) ── */
+  --color-gray-50: #1a1a1a;
+  --color-gray-100: #2f2f2f;
+  --color-gray-200: #3a3a3a;
+  --color-gray-300: #4a4a4a;
+  --color-gray-400: #6b6b6a;
+  --color-gray-500: #9b9b9a;
+  --color-gray-600: #b0b0af;
+  --color-gray-700: #cececd;
+  --color-gray-800: #ededec;
+  --color-gray-900: #fbfbfa;
+
+  /* ── Background ── */
+  --bg-primary: #1a1a1a;
+  --bg-secondary: #1f1f1f;
+  --bg-tertiary: #2a2a2a;
+  --bg-elevated: #252525;
+  --bg-code: #11111b;
+
+  /* ── Foreground / Text ── */
+  --text-primary: #fbfbfa;
+  --text-secondary: #cececd;
+  --text-tertiary: #9b9b9a;
+  --text-placeholder: #6b6b6a;
+  --text-inverse: #1a1a1a;
+  --text-code: #cdd6f4;
+
+  /* ── Border ── */
+  --border-color: #3a3a3a;
+  --border-color-hover: #4a4a4a;
+  --border-color-active: var(--color-primary);
+  --border-color-split: #2f2f2f;
+
+  /* ── Shadow (darker ambient for dark mode) ── */
+  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.2);
+  --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.25), 0 1px 2px rgba(0, 0, 0, 0.15);
+  --shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.3), 0 2px 4px rgba(0, 0, 0, 0.15);
+  --shadow-xl: 0 8px 32px rgba(0, 0, 0, 0.35), 0 2px 8px rgba(0, 0, 0, 0.15);
+
+  /* ── Code Theme (Catppuccin Mocha — unchanged, already dark) ── */
+  --code-bg: #11111b;
+  --code-fg: #cdd6f4;
+  --code-keyword: #cba6f7;
+  --code-string: #a6e3a1;
+  --code-number: #fab387;
+  --code-comment: #6c7086;
+  --code-function: #89b4fa;
+  --code-variable: #f38ba8;
+  --code-type: #f9e2af;
+  --code-added-bg: rgba(166, 227, 161, 0.2);
+  --code-removed-bg: rgba(243, 139, 168, 0.2);
 }
diff --git a/src/agentkit/server/routes/skills.py b/src/agentkit/server/routes/skills.py
index 77ed2a9..f7dcb91 100644
--- a/src/agentkit/server/routes/skills.py
+++ b/src/agentkit/server/routes/skills.py
@@ -160,6 +160,30 @@ async def list_skills(req: Request):
     ]
 
 
+@router.get("/skills/mention-suggest")
+async def mention_suggest(q: str = "", req: Request = None):
+    """Suggest skills for @-mention autocomplete.
+
+    Returns up to 8 skills matching the query string, with name and description
+    for the MentionDropdown component.
+    """
+    skill_registry = req.app.state.skill_registry
+    skills = skill_registry.list_skills()
+    query = q.lower()
+
+    if query:
+        skills = [
+            s for s in skills
+            if query in s.name.lower()
+            or (s.config.description and query in s.config.description.lower())
+        ]
+
+    return [
+        {"name": s.name, "description": s.config.description or ""}
+        for s in skills[:8]
+    ]
+
+
 @router.post("/skills/install")
 async def install_skill(request: InstallSkillRequest, req: Request):
     """Search for and install a skill by name.
diff --git a/src/agentkit/tools/computer_use_session.py b/src/agentkit/tools/computer_use_session.py
index d185fcf..78bedc3 100644
--- a/src/agentkit/tools/computer_use_session.py
+++ b/src/agentkit/tools/computer_use_session.py
@@ -1,12 +1,16 @@
 """ComputerUseSession - 虚拟桌面会话管理
 
-管理虚拟桌面会话（Docker 沙箱），维护操作上下文。
-提供 InMemoryComputerUseSession 用于测试，DockerComputerUseSession 用于生产。
+管理虚拟桌面会话，维护操作上下文。
+提供 InMemoryComputerUseSession 用于测试，LocalComputerUseSession 用于本地桌面，
+DockerComputerUseSession 用于 Docker 沙箱（stub）。
 """
 
 from __future__ import annotations
 
+import base64
+import io
 import logging
+import platform
 import time
 import uuid
 from abc import ABC, abstractmethod
@@ -248,6 +252,124 @@ class InMemoryComputerUseSession(ComputerUseSession):
         )
 
 
+class LocalComputerUseSession(ComputerUseSession):
+    """本地桌面会话，使用 pyautogui + screencapture。
+
+    在本地桌面执行真实的 UI 操作。需要辅助功能权限（macOS）。
+    适用于开发/演示环境，生产环境应使用 DockerComputerUseSession。
+    """
+
+    def __init__(
+        self,
+        session_id: str | None = None,
+        screen_width: int = 1280,
+        screen_height: int = 720,
+    ):
+        super().__init__(
+            session_id=session_id,
+            screen_width=screen_width,
+            screen_height=screen_height,
+        )
+        self._pyautogui: Any = None
+
+    async def start(self) -> None:
+        """启动本地桌面会话"""
+        try:
+            import pyautogui
+            self._pyautogui = pyautogui
+            pyautogui.FAILSAFE = True
+            pyautogui.PAUSE = 0.1
+        except ImportError:
+            raise RuntimeError(
+                "pyautogui is required for LocalComputerUseSession. "
+                "Install with: pip install pyautogui"
+            )
+        self._started = True
+        logger.info("Local desktop session started: %s", self.session_id[:8])
+
+    async def stop(self) -> None:
+        """停止本地桌面会话"""
+        self._started = False
+        self._pyautogui = None
+        logger.info("Local desktop session stopped: %s", self.session_id[:8])
+
+    async def screenshot(self) -> ActionResult:
+        """截取本地桌面屏幕"""
+        if not self._started:
+            return ActionResult(success=False, action="screenshot", error="Session not started")
+
+        try:
+            img = self._pyautogui.screenshot()
+            buf = io.BytesIO()
+            img.save(buf, format="PNG")
+            screenshot_b64 = base64.b64encode(buf.getvalue()).decode("ascii")
+            return ActionResult(
+                success=True,
+                action="screenshot",
+                output=f"Screenshot {img.size[0]}x{img.size[1]}",
+                screenshot_base64=screenshot_b64,
+            )
+        except Exception as e:
+            return ActionResult(success=False, action="screenshot", error=str(e))
+
+    async def execute_action(self, action: str, **params: Any) -> ActionResult:
+        """在本地桌面执行 UI 操作"""
+        if not self._started:
+            return ActionResult(success=False, action=action, error="Session not started")
+
+        try:
+            result = self._execute_local_action(action, **params)
+            self.record_action(action, params, result)
+            return result
+        except Exception as e:
+            return ActionResult(success=False, action=action, error=str(e))
+
+    def _execute_local_action(self, action: str, **params: Any) -> ActionResult:
+        """执行本地 UI 操作"""
+        pg = self._pyautogui
+
+        if action == "click":
+            x, y = params.get("x", 0), params.get("y", 0)
+            button = params.get("button", "left")
+            pg.click(x, y, button=button)
+            return ActionResult(success=True, action="click", output=f"Clicked at ({x}, {y})")
+
+        if action == "type":
+            text = params.get("text", "")
+            pg.typewrite(text) if platform.system() != "Darwin" else pg.write(text)
+            return ActionResult(success=True, action="type", output=f"Typed: {text}")
+
+        if action == "scroll":
+            direction = params.get("direction", "down")
+            amount = params.get("amount", 3)
+            clicks = amount if direction == "down" else -amount
+            pg.scroll(clicks)
+            return ActionResult(success=True, action="scroll", output=f"Scrolled {direction} by {amount}")
+
+        if action == "drag":
+            sx, sy = params.get("start_x", 0), params.get("start_y", 0)
+            ex, ey = params.get("end_x", 0), params.get("end_y", 0)
+            pg.moveTo(sx, sy)
+            pg.dragTo(ex, ey, duration=0.5)
+            return ActionResult(success=True, action="drag", output=f"Dragged from ({sx},{sy}) to ({ex},{ey})")
+
+        if action == "key":
+            key_name = params.get("key_name", "")
+            keys = key_name.split("+")
+            if len(keys) > 1:
+                pg.hotkey(*keys)
+            else:
+                pg.press(key_name)
+            return ActionResult(success=True, action="key", output=f"Pressed key: {key_name}")
+
+        if action == "wait":
+            duration = params.get("duration", 1.0)
+            time.sleep(duration)
+            return ActionResult(success=True, action="wait", output=f"Waited {duration}s")
+
+        return ActionResult(success=False, action=action, error=f"Unknown action: {action}")
+
+
 class DockerComputerUseSession(ComputerUseSession):
     """Docker 沙箱虚拟桌面会话
 
diff --git a/tests/integration/test_gap_closure.py b/tests/integration/test_gap_closure.py
new file mode 100644
index 0000000..0dde6f3
--- /dev/null
+++ b/tests/integration/test_gap_closure.py
@@ -0,0 +1,163 @@
+"""Gap closure integration tests — dark theme, @-mention API, LocalComputerUseSession."""
+
+import pytest
+from unittest.mock import MagicMock, patch
+
+from agentkit.quality.cascade_state_store import (
+    InMemoryCascadeStateStore,
+    create_cascade_state_store,
+)
+from agentkit.llm.providers.usage_store import (
+    InMemoryUsageStore,
+    create_usage_store,
+)
+from agentkit.tools.computer_use_session import (
+    InMemoryComputerUseSession,
+    LocalComputerUseSession,
+    ComputerUseSessionManager,
+)
+
+
+# ---------------------------------------------------------------------------
+# Dark theme: CSS token validation (smoke test)
+# ---------------------------------------------------------------------------
+
+
+class TestDarkThemeTokens:
+    """Verify dark theme CSS tokens exist in tokens.css."""
+
+    def test_dark_theme_tokens_file_contains_dark_selector(self):
+        import pathlib
+        tokens_path = pathlib.Path(__file__).parent.parent.parent / (
+            "src/agentkit/server/frontend/src/styles/tokens.css"
+        )
+        if not tokens_path.exists():
+            pytest.skip("Frontend tokens.css not found")
+        content = tokens_path.read_text()
+        assert '[data-theme="dark"]' in content
+        assert '--bg-primary: #1a1a1a' in content
+        assert '--text-primary: #fbfbfa' in content
+        assert '--border-color: #3a3a3a' in content
+
+    def test_theme_store_exists(self):
+        import pathlib
+        store_path = pathlib.Path(__file__).parent.parent.parent / (
+            "src/agentkit/server/frontend/src/stores/theme.ts"
+        )
+        if not store_path.exists():
+            pytest.skip("Theme store not found")
+        content = store_path.read_text()
+        assert 'useThemeStore' in content
+        assert 'toggle' in content
+        assert 'resolvedMode' in content
+        assert 'localStorage' in content
+
+
+# ---------------------------------------------------------------------------
+# @-mention API: mention-suggest endpoint
+# ---------------------------------------------------------------------------
+
+
+class TestMentionSuggestAPI:
+    """Test the /skills/mention-suggest endpoint logic."""
+
+    def _make_skill(self, name, description):
+        skill = MagicMock()
+        skill.name = name
+        skill.config.description = description
+        return skill
+
+    def test_mention_suggest_filters_by_name(self):
+        """Verify the filtering logic used by the endpoint."""
+        skills = [
+            self._make_skill("geo_pipeline", "GEO pipeline skill"),
+            self._make_skill("code_reviewer", "Code review skill"),
+            self._make_skill("data_analyst", "Data analysis skill"),
+        ]
+        query = "geo"
+        filtered = [
+            s for s in skills
+            if query in s.name.lower()
+            or (s.config.description and query in s.config.description.lower())
+        ]
+        assert len(filtered) == 1
+        assert filtered[0].name == "geo_pipeline"
+
+    def test_mention_suggest_filters_by_description(self):
+        skills = [
+            self._make_skill("skill_a", "GEO pipeline skill"),
+            self._make_skill("skill_b", "Code review skill"),
+        ]
+        query = "review"
+        filtered = [
+            s for s in skills
+            if query in s.name.lower()
+            or (s.config.description and query in s.config.description.lower())
+        ]
+        assert len(filtered) == 1
+        assert filtered[0].name == "skill_b"
+
+    def test_mention_suggest_limits_to_8(self):
+        skills = [self._make_skill(f"skill_{i}", "") for i in range(20)]
+        result = skills[:8]
+        assert len(result) == 8
+
+    def test_mention_suggest_empty_query(self):
+        skills = [
+            self._make_skill("skill_a", "desc"),
+            self._make_skill("skill_b", "desc"),
+        ]
+        query = ""
+        filtered = [
+            s for s in skills
+            if query in s.name.lower()
+            or (s.config.description and query in s.config.description.lower())
+        ]
+        assert len(filtered) == 2
+
+
+# ---------------------------------------------------------------------------
+# LocalComputerUseSession
+# ---------------------------------------------------------------------------
+
+
+class TestLocalComputerUseSession:
+    """Test LocalComputerUseSession (without actual pyautogui)."""
+
+    def test_inherits_from_base(self):
+        assert issubclass(LocalComputerUseSession, InMemoryComputerUseSession.__mro__[1])
+
+    def test_start_without_pyautogui_raises(self):
+        """If pyautogui is not installed, start should raise RuntimeError."""
+        import asyncio
+        session = LocalComputerUseSession()
+        with patch.dict("sys.modules", {"pyautogui": None}):
+            with pytest.raises(RuntimeError, match="pyautogui"):
+                asyncio.run(session.start())
+
+    def test_session_manager_with_local_factory(self):
+        manager = ComputerUseSessionManager(session_factory=LocalComputerUseSession)
+        session = manager.get_or_create(session_id="test-local")
+        assert isinstance(session, LocalComputerUseSession)
+
+
+# ---------------------------------------------------------------------------
+# Factory session_ttl propagation (regression test)
+# ---------------------------------------------------------------------------
+
+
+class TestFactorySessionTTL:
+    """Ensure session_ttl is propagated through factories."""
+
+    def test_cascade_store_memory_with_custom_ttl(self):
+        store = create_cascade_state_store(backend="memory", session_ttl=7200)
+        assert isinstance(store, InMemoryCascadeStateStore)
+        assert store._session_ttl == 7200
+
+    def test_usage_store_memory_backend(self):
+        store = create_usage_store(backend="memory")
+        assert isinstance(store, InMemoryUsageStore)
+
+    def test_cascade_store_auto_backend(self):
+        store = create_cascade_state_store(backend="auto")
+        assert store._session_ttl == 86400  # default
diff --git a/tests/unit/llm/test_usage_store.py b/tests/unit/llm/test_usage_store.py
new file mode 100644
index 0000000..d9ce3d4
--- /dev/null
+++ b/tests/unit/llm/test_usage_store.py
@@ -0,0 +1,229 @@
+"""Unit tests for UsageStore (U4 — UsageStore Persistence)."""
+
+import pytest
+from datetime import datetime, timedelta, timezone
+
+from agentkit.llm.protocol import TokenUsage
+from agentkit.llm.providers.usage_store import (
+    InMemoryUsageStore,
+    RedisUsageStore,
+    UsageRecord,
+    UsageBucket,
+    UsageSummary,
+    UsageStore,
+    create_usage_store,
+)
+
+
+# ---------------------------------------------------------------------------
+# InMemoryUsageStore
+# ---------------------------------------------------------------------------
+
+
+class TestInMemoryUsageStore:
+    """Tests for InMemoryUsageStore."""
+
+    def test_implements_protocol(self):
+        store = InMemoryUsageStore()
+        assert isinstance(store, UsageStore)
+
+    def test_record_single(self):
+        store = InMemoryUsageStore()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        summary = store.get_usage()
+        assert summary.total_tokens == 150
+        assert summary.total_cost == 0.05
+        assert len(summary.records) == 1
+
+    def test_record_multiple(self):
+        store = InMemoryUsageStore()
+        usage1 = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        usage2 = TokenUsage(prompt_tokens=200, completion_tokens=100)
+        store.record("agent1", "gpt-4", usage1, cost=0.05, latency_ms=200)
+        store.record("agent1", "gpt-4", usage2, cost=0.10, latency_ms=300)
+        summary = store.get_usage()
+        assert summary.total_tokens == 450
+        assert abs(summary.total_cost - 0.15) < 1e-6
+        assert len(summary.records) == 2
+
+    def test_get_usage_by_agent(self):
+        store = InMemoryUsageStore()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        store.record("agent2", "gpt-4", usage, cost=0.05, latency_ms=200)
+        summary = store.get_usage(agent_name="agent1")
+        assert len(summary.records) == 1
+        assert summary.records[0].agent_name == "agent1"
+
+    def test_get_usage_by_time_range(self):
+        store = InMemoryUsageStore()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+
+        # Query with start_time in the future — should return empty
+        future = datetime.now(timezone.utc) + timedelta(hours=1)
+        summary = store.get_usage(start_time=future)
+        assert len(summary.records) == 0
+
+        # Query with end_time in the past — should return empty
+        past = datetime.now(timezone.utc) - timedelta(hours=1)
+        summary = store.get_usage(end_time=past)
+        assert len(summary.records) == 0
+
+        # Query with wide range — should return the record
+        start = datetime.now(timezone.utc) - timedelta(hours=1)
+        end = datetime.now(timezone.utc) + timedelta(hours=1)
+        summary = store.get_usage(start_time=start, end_time=end)
+        assert len(summary.records) == 1
+
+    def test_get_usage_by_model(self):
+        store = InMemoryUsageStore()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        store.record("agent1", "gpt-3.5", usage, cost=0.01, latency_ms=100)
+        summary = store.get_usage()
+        assert "gpt-4" in summary.by_model
+        assert "gpt-3.5" in summary.by_model
+        assert summary.by_model["gpt-4"]["count"] == 1
+        assert summary.by_model["gpt-3.5"]["count"] == 1
+
+    def test_get_usage_empty(self):
+        store = InMemoryUsageStore()
+        summary = store.get_usage()
+        assert summary.total_tokens == 0
+        assert summary.total_cost == 0.0
+        assert len(summary.records) == 0
+
+    def test_max_records_trimming(self):
+        store = InMemoryUsageStore()
+        store.MAX_RECORDS = 5
+        usage = TokenUsage(prompt_tokens=1, completion_tokens=1)
+        for i in range(10):
+            store.record(f"agent{i}", "gpt-4", usage, cost=0.01, latency_ms=100)
+        assert len(store._records) == 5
+        # Should keep the last 5 records
+        assert store._records[0].agent_name == "agent5"
+
+    def test_usage_record_timestamp(self):
+        store = InMemoryUsageStore()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        rec = store.get_usage().records[0]
+        assert rec.timestamp != ""
+        # Should be parseable as ISO 8601
+        datetime.fromisoformat(rec.timestamp)
+
+
+# ---------------------------------------------------------------------------
+# UsageRecord / UsageBucket / UsageSummary dataclasses
+# ---------------------------------------------------------------------------
+
+
+class TestDataclasses:
+    def test_usage_record_auto_timestamp(self):
+        rec = UsageRecord(
+            agent_name="a", model="m",
+            prompt_tokens=1, completion_tokens=1,
+            total_tokens=2, cost=0.01, latency_ms=100,
+        )
+        assert rec.timestamp != ""
+
+    def test_usage_record_explicit_timestamp(self):
+        rec = UsageRecord(
+            agent_name="a", model="m",
+            prompt_tokens=1, completion_tokens=1,
+            total_tokens=2, cost=0.01, latency_ms=100,
+            timestamp="2026-01-01T00:00:00+00:00",
+        )
+        assert rec.timestamp == "2026-01-01T00:00:00+00:00"
+
+    def test_usage_bucket_defaults(self):
+        bucket = UsageBucket()
+        assert bucket.prompt_tokens == 0
+        assert bucket.completion_tokens == 0
+        assert bucket.total_tokens == 0
+        assert bucket.cost == 0.0
+        assert bucket.count == 0
+
+    def test_usage_summary_defaults(self):
+        summary = UsageSummary()
+        assert summary.total_tokens == 0
+        assert summary.total_cost == 0.0
+        assert summary.by_model == {}
+        assert summary.records == []
+
+
+# ---------------------------------------------------------------------------
+# RedisUsageStore (mocked)
+# ---------------------------------------------------------------------------
+
+
+class TestRedisUsageStoreMocked:
+    """Tests for RedisUsageStore with mocked Redis."""
+
+    def _make_store(self):
+        store = RedisUsageStore(redis_url="redis://localhost:6379")
+        return store
+
+    def test_implements_protocol(self):
+        store = self._make_store()
+        assert isinstance(store, UsageStore)
+
+    def test_degrade_to_fallback(self):
+        store = self._make_store()
+        assert not store._degraded
+        store._degrade_to_fallback()
+        assert store._degraded
+        assert store._fallback is not None
+
+    def test_record_degraded_uses_fallback(self):
+        store = self._make_store()
+        store._degrade_to_fallback()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        # Should be in fallback
+        summary = store._fallback.get_usage()
+        assert len(summary.records) == 1
+
+    def test_get_usage_degraded_uses_fallback(self):
+        store = self._make_store()
+        store._degrade_to_fallback()
+        usage = TokenUsage(prompt_tokens=100, completion_tokens=50)
+        store._fallback.record("agent1", "gpt-4", usage, cost=0.05, latency_ms=200)
+        summary = store.get_usage()
+        assert len(summary.records) == 1
+
+    def test_get_usage_degraded_no_fallback_returns_empty(self):
+        store = self._make_store()
+        store._degraded = True
+        # No fallback set — should return empty
+        summary = store.get_usage()
+        assert summary.total_tokens == 0
+
+    def test_today_key_format(self):
+        store = self._make_store()
+        key = store._today_key()
+        # Should be YYYY-MM-DD
+        assert len(key) == 10
+        assert key[4] == "-"
+
+
+# ---------------------------------------------------------------------------
+# Factory
+# ---------------------------------------------------------------------------
+
+
+class TestCreateUsageStore:
+    def test_memory_backend(self):
+        store = create_usage_store(backend="memory")
+        assert isinstance(store, InMemoryUsageStore)
+
+    def test_auto_backend_returns_store(self):
+        store = create_usage_store(backend="auto")
+        assert isinstance(store, (InMemoryUsageStore, RedisUsageStore))
+
+    def test_redis_backend_returns_store(self):
+        store = create_usage_store(backend="redis")
+        # May be InMemory if redis package unavailable
+        assert isinstance(store, (InMemoryUsageStore, RedisUsageStore))
diff --git a/tests/unit/quality/test_cascade_state_store.py b/tests/unit/quality/test_cascade_state_store.py
new file mode 100644
index 0000000..db9b0f8
--- /dev/null
+++ b/tests/unit/quality/test_cascade_state_store.py
@@ -0,0 +1,274 @@
+"""Unit tests for CascadeStateStore (U5 — CascadeStateStore Persistence)."""
+
+import pytest
+import time
+from unittest.mock import MagicMock, patch
+
+from agentkit.quality.cascade_state_store import (
+    CascadeStateStore,
+    InMemoryCascadeStateStore,
+    RedisCascadeStateStore,
+    create_cascade_state_store,
+)
+
+
+# ---------------------------------------------------------------------------
+# InMemoryCascadeStateStore
+# ---------------------------------------------------------------------------
+
+
+class TestInMemoryCascadeStateStore:
+    """Tests for InMemoryCascadeStateStore."""
+
+    def test_implements_protocol(self):
+        store = InMemoryCascadeStateStore()
+        assert isinstance(store, CascadeStateStore)
+
+    def test_increment_interaction(self):
+        store = InMemoryCascadeStateStore()
+        assert store.increment_interaction("s1") == 1
+        assert store.increment_interaction("s1") == 2
+        assert store.increment_interaction("s1") == 3
+
+    def test_increment_different_sessions(self):
+        store = InMemoryCascadeStateStore()
+        assert store.increment_interaction("s1") == 1
+        assert store.increment_interaction("s2") == 1
+        assert store.increment_interaction("s1") == 2
+
+    def test_get_interaction(self):
+        store = InMemoryCascadeStateStore()
+        store.increment_interaction("s1")
+        store.increment_interaction("s1")
+        assert store.get_interaction("s1") == 2
+
+    def test_get_interaction_nonexistent(self):
+        store = InMemoryCascadeStateStore()
+        assert store.get_interaction("unknown") == 0
+
+    def test_set_and_get_depth(self):
+        store = InMemoryCascadeStateStore()
+        store.set_depth("s1", 3)
+        assert store.get_depth("s1") == 3
+
+    def test_get_depth_nonexistent(self):
+        store = InMemoryCascadeStateStore()
+        assert store.get_depth("unknown") == 0
+
+    def test_reset(self):
+        store = InMemoryCascadeStateStore()
+        store.increment_interaction("s1")
+        store.increment_interaction("s1")
+        store.set_depth("s1", 2)
+        store.reset("s1")
+        assert store.get_interaction("s1") == 0
+        assert store.get_depth("s1") == 0
+
+    def test_reset_nonexistent_no_error(self):
+        store = InMemoryCascadeStateStore()
+        store.reset("nonexistent")  # Should not raise
+
+    def test_ttl_expiry_interaction(self):
+        store = InMemoryCascadeStateStore(session_ttl=1)  # 1 second TTL
+        store.increment_interaction("s1")
+        assert store.get_interaction("s1") == 1
+        time.sleep(1.1)
+        # After TTL, should return 0 (expired)
+        assert store.get_interaction("s1") == 0
+
+    def test_ttl_expiry_depth(self):
+        store = InMemoryCascadeStateStore(session_ttl=1)
+        store.set_depth("s1", 5)
+        assert store.get_depth("s1") == 5
+        time.sleep(1.1)
+        assert store.get_depth("s1") == 0
+
+    def test_ttl_cleanup_on_increment(self):
+        store = InMemoryCascadeStateStore(session_ttl=1)
+        store.increment_interaction("s1")
+        store.increment_interaction("s2")
+        time.sleep(1.1)
+        # Incrementing s3 should trigger cleanup of s1 and s2
+        store.increment_interaction("s3")
+        assert "s1" not in store._interaction_counts
+        assert "s2" not in store._interaction_counts
+        assert store._interaction_counts.get("s3") == 1
+
+    def test_touch_refreshes_ttl(self):
+        store = InMemoryCascadeStateStore(session_ttl=2)
+        store.increment_interaction("s1")
+        time.sleep(1.0)
+        # Touch refreshes the timestamp
+        store.increment_interaction("s1")
+        time.sleep(1.0)
+        # Should still be alive (1s < 2s since last touch)
+        assert store.get_interaction("s1") == 2
+
+    def test_default_session_ttl(self):
+        store = InMemoryCascadeStateStore()
+        assert store._session_ttl == 86400
+
+    def test_custom_session_ttl(self):
+        store = InMemoryCascadeStateStore(session_ttl=3600)
+        assert store._session_ttl == 3600
+
+
+# ---------------------------------------------------------------------------
+# RedisCascadeStateStore (mocked)
+# ---------------------------------------------------------------------------
+
+
+class TestRedisCascadeStateStoreMocked:
+    """Tests for RedisCascadeStateStore with mocked Redis."""
+
+    def test_implements_protocol(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        assert isinstance(store, CascadeStateStore)
+
+    def test_degrade_to_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        assert not store._degraded
+        store._degrade_to_fallback()
+        assert store._degraded
+        assert isinstance(store._fallback, InMemoryCascadeStateStore)
+
+    def test_increment_degraded_uses_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        store._degrade_to_fallback()
+        result = store.increment_interaction("s1")
+        assert result == 1
+        assert store._fallback.get_interaction("s1") == 1
+
+    def test_get_interaction_degraded_uses_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        store._degrade_to_fallback()
+        store._fallback.increment_interaction("s1")
+        assert store.get_interaction("s1") == 1
+
+    def test_set_depth_degraded_uses_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        store._degrade_to_fallback()
+        store.set_depth("s1", 3)
+        assert store._fallback.get_depth("s1") == 3
+
+    def test_get_depth_degraded_uses_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        store._degrade_to_fallback()
+        store._fallback.set_depth("s1", 5)
+        assert store.get_depth("s1") == 5
+
+    def test_reset_degraded_uses_fallback(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        store._degrade_to_fallback()
+        store._fallback.increment_interaction("s1")
+        store.reset("s1")
+        assert store._fallback.get_interaction("s1") == 0
+
+    def test_increment_redis_failure_degrades(self):
+        store = RedisCascadeStateStore(redis_url="redis://nonexistent:6379")
+        # Will fail to connect and degrade
+        result = store.increment_interaction("s1")
+        assert store._degraded
+        assert result >= 0  # Should return something (fallback or 0)
+
+    def test_custom_session_ttl(self):
+        store = RedisCascadeStateStore(
+            redis_url="redis://localhost:6379", session_ttl=3600
+        )
+        assert store._session_ttl == 3600
+
+    def test_default_session_ttl(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        assert store._session_ttl == 86400
+
+    def test_increment_with_mock_redis(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        mock_redis = MagicMock()
+        mock_pipeline = MagicMock()
+        mock_pipeline.incr.return_value = mock_pipeline
+        mock_pipeline.expire.return_value = mock_pipeline
+        mock_pipeline.execute.return_value = [1, True]
+        mock_redis.pipeline.return_value = mock_pipeline
+        store._sync_redis = mock_redis
+
+        result = store.increment_interaction("s1")
+        assert result == 1
+        mock_pipeline.incr.assert_called_once()
+        mock_pipeline.expire.assert_called_once()
+
+    def test_get_interaction_with_mock_redis(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        mock_redis = MagicMock()
+        mock_redis.get.return_value = "3"
+        store._sync_redis = mock_redis
+
+        result = store.get_interaction("s1")
+        assert result == 3
+
+    def test_get_interaction_redis_returns_none(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        mock_redis = MagicMock()
+        mock_redis.get.return_value = None
+        store._sync_redis = mock_redis
+
+        result = store.get_interaction("s1")
+        assert result == 0
+
+    def test_set_depth_with_mock_redis(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        mock_redis = MagicMock()
+        mock_pipeline = MagicMock()
+        mock_pipeline.set.return_value = mock_pipeline
+        mock_pipeline.expire.return_value = mock_pipeline
+        mock_pipeline.execute.return_value = [True, True]
+        mock_redis.pipeline.return_value = mock_pipeline
+        store._sync_redis = mock_redis
+
+        store.set_depth("s1", 3)
+        mock_pipeline.set.assert_called_once()
+        mock_pipeline.expire.assert_called_once()
+
+    def test_reset_with_mock_redis(self):
+        store = RedisCascadeStateStore(redis_url="redis://localhost:6379")
+        mock_redis = MagicMock()
+        mock_pipeline = MagicMock()
+        mock_pipeline.delete.return_value = mock_pipeline
+        mock_pipeline.execute.return_value = [1, 1]
+        mock_redis.pipeline.return_value = mock_pipeline
+        store._sync_redis = mock_redis
+
+        store.reset("s1")
+        assert mock_pipeline.delete.call_count == 2
+
+
+# ---------------------------------------------------------------------------
+# Factory
+# ---------------------------------------------------------------------------
+
+
+class TestCreateCascadeStateStore:
+    def test_memory_backend(self):
+        store = create_cascade_state_store(backend="memory")
+        assert isinstance(store, InMemoryCascadeStateStore)
+
+    def test_auto_backend_returns_store(self):
+        store = create_cascade_state_store(backend="auto")
+        assert isinstance(store, (InMemoryCascadeStateStore, RedisCascadeStateStore))
+
+    def test_redis_backend_returns_store(self):
+        store = create_cascade_state_store(backend="redis")
+        assert isinstance(store, (InMemoryCascadeStateStore, RedisCascadeStateStore))
+
+    def test_session_ttl_passed_to_redis(self):
+        store = create_cascade_state_store(
+            backend="redis", session_ttl=7200
+        )
+        if isinstance(store, RedisCascadeStateStore):
+            assert store._session_ttl == 7200
+
+    def test_session_ttl_passed_to_memory(self):
+        store = create_cascade_state_store(
+            backend="memory", session_ttl=7200
+        )
+        assert isinstance(store, InMemoryCascadeStateStore)
+        assert store._session_ttl == 7200