diff --git a/frontend/src/api/ai.ts b/frontend/src/api/ai.ts
new file mode 100644
index 0000000..dc69aed
--- /dev/null
+++ b/frontend/src/api/ai.ts
@@ -0,0 +1,198 @@
+/**
+ * AI Assistant plugin API client.
+ *
+ * All requests use the shared `apiClient` (`baseURL: '/api/v1'`) and target the
+ * AI Assistant plugin routes under `/ai/...`.
+ */
+
+import { apiDelete, apiGet, apiPost, apiPut } from './client';
+
+// ─── Types ───
+
+export interface AIProvider {
+  id: string;
+  name: string;
+  provider_type: string;
+  api_key: string;
+  base_url: string;
+  is_active: boolean;
+  is_default: boolean;
+  config: Record<string, unknown>;
+  created_at?: string;
+  updated_at?: string;
+}
+
+export interface AIModel {
+  id: string;
+  provider_id: string;
+  model_id: string;
+  display_name: string;
+  context_window: number;
+  supports_tools: boolean;
+  supports_streaming: boolean;
+  is_active: boolean;
+  config: Record<string, unknown>;
+}
+
+export interface AIPreset {
+  id: string;
+  name: string;
+  model_id: string;
+  provider_id: string | null;
+  temperature: number;
+  max_tokens: number;
+  top_p: number;
+  system_prompt: string;
+  config: Record<string, unknown>;
+  is_active: boolean;
+}
+
+export interface AIAgent {
+  id: string;
+  name: string;
+  description: string;
+  system_prompt: string;
+  preset_id: string | null;
+  tool_ids: string[];
+  is_default: boolean;
+  is_active: boolean;
+  config: Record<string, unknown>;
+  created_at?: string;
+  updated_at?: string;
+}
+
+export interface ChatSession {
+  id: string;
+  user_id: string;
+  agent_id: string | null;
+  title: string;
+  is_pinned: boolean;
+  is_sidebar: boolean;
+  created_at?: string;
+  updated_at?: string;
+}
+
+export interface ChatMessage {
+  id: string;
+  session_id: string;
+  role: string;
+  content: string;
+  tool_calls?: Record<string, unknown>[];
+  tool_results?: Record<string, unknown>[];
+  tokens: number;
+  model_used: string;
+  created_at?: string;
+}
+
+export interface AITool {
+  name: string;
+  description: string;
+  parameters: Record<string, unknown>;
+  plugin_name: string;
+  required_permission: string | null;
+  category: string;
+}
+
+// ─── Providers ───
+
+export const fetchProviders = () => apiGet<AIProvider[]>('/ai/providers');
+export const createProvider = (data: Partial<AIProvider>) => apiPost<AIProvider>('/ai/providers', data);
+export const updateProvider = (id: string, data: Partial<AIProvider>) => apiPut<AIProvider>(`/ai/providers/${id}`, data);
+export const deleteProvider = (id: string) => apiDelete(`/ai/providers/${id}`);
+
+// ─── Models ───
+
+export const fetchModels = (providerId?: string) =>
+  apiGet<AIModel[]>('/ai/models', { params: providerId ? { provider_id: providerId } : {} });
+export const createModel = (data: Partial<AIModel>) => apiPost<AIModel>('/ai/models', data);
+export const updateModel = (id: string, data: Partial<AIModel>) => apiPut<AIModel>(`/ai/models/${id}`, data);
+export const deleteModel = (id: string) => apiDelete(`/ai/models/${id}`);
+
+// ─── Presets ───
+
+export const fetchPresets = () => apiGet<AIPreset[]>('/ai/presets');
+export const createPreset = (data: Partial<AIPreset>) => apiPost<AIPreset>('/ai/presets', data);
+export const updatePreset = (id: string, data: Partial<AIPreset>) => apiPut<AIPreset>(`/ai/presets/${id}`, data);
+export const deletePreset = (id: string) => apiDelete(`/ai/presets/${id}`);
+
+// ─── Agents ───
+
+export const fetchAgents = () => apiGet<AIAgent[]>('/ai/agents');
+export const createAgent = (data: Partial<AIAgent>) => apiPost<AIAgent>('/ai/agents', data);
+export const updateAgent = (id: string, data: Partial<AIAgent>) => apiPut<AIAgent>(`/ai/agents/${id}`, data);
+export const deleteAgent = (id: string) => apiDelete(`/ai/agents/${id}`);
+
+// ─── Tools ───
+
+export const fetchTools = () => apiGet<AITool[]>('/ai/tools');
+
+// ─── Sessions ───
+
+export const fetchSessions = (isSidebar?: boolean) =>
+  apiGet<ChatSession[]>('/ai/sessions', { params: isSidebar !== undefined ? { is_sidebar: isSidebar } : {} });
+export const createSession = (data: { title?: string; agent_id?: string; is_sidebar?: boolean }) =>
+  apiPost<ChatSession>('/ai/sessions', data);
+export const updateSession = (id: string, data: Partial<ChatSession>) =>
+  apiPut<ChatSession>(`/ai/sessions/${id}`, data);
+export const deleteSession = (id: string) => apiDelete(`/ai/sessions/${id}`);
+
+// ─── Messages ───
+
+export const fetchMessages = (sessionId: string) =>
+  apiGet<ChatMessage[]>(`/ai/sessions/${sessionId}/messages`);
+
+// ─── Streaming Chat ───
+
+export interface StreamEvent {
+  type: 'token' | 'tool_calls' | 'tool_result' | 'done' | 'error';
+  content?: string;
+  tool?: string;
+  result?: string;
+  tools?: string[];
+}
+
+export async function* streamChat(
+  sessionId: string,
+  content: string,
+  agentId?: string
+): AsyncGenerator<StreamEvent> {
+  const response = await fetch(`/api/v1/ai/sessions/${sessionId}/stream`, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+    },
+    credentials: 'include',
+    body: JSON.stringify({ content, agent_id: agentId }),
+  });
+
+  if (!response.ok) {
+    throw new Error(`Stream failed: ${response.status}`);
+  }
+
+  const reader = response.body?.getReader();
+  if (!reader) throw new Error('No response body');
+
+  const decoder = new TextDecoder();
+  let buffer = '';
+
+  while (true) {
+    const { done, value } = await reader.read();
+    if (done) break;
+
+    buffer += decoder.decode(value, { stream: true });
+    const lines = buffer.split('\n');
+    buffer = lines.pop() || '';
+
+    for (const line of lines) {
+      if (line.startsWith('data: ')) {
+        const data = line.slice(6).trim();
+        if (data === '[DONE]') return;
+        try {
+          yield JSON.parse(data);
+        } catch {
+          // skip invalid JSON
+        }
+      }
+    }
+  }
+}
diff --git a/frontend/src/components/ai/ChatWindow.tsx b/frontend/src/components/ai/ChatWindow.tsx
new file mode 100644
index 0000000..d2ac8b0
--- /dev/null
+++ b/frontend/src/components/ai/ChatWindow.tsx
@@ -0,0 +1,154 @@
+import React, { useState, useRef, useEffect } from 'react';
+import clsx from 'clsx';
+import { streamChat, fetchMessages, type ChatMessage } from '@/api/ai';
+
+interface ChatWindowProps {
+  sessionId: string;
+  agentId?: string | null;
+  className?: string;
+  compact?: boolean;
+}
+
+export function ChatWindow({ sessionId, agentId, className, compact }: ChatWindowProps) {
+  const [messages, setMessages] = useState<ChatMessage[]>([]);
+  const [input, setInput] = useState('');
+  const [isStreaming, setIsStreaming] = useState(false);
+  const [streamingContent, setStreamingContent] = useState('');
+  const [toolStatus, setToolStatus] = useState<string | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const scrollRef = useRef<HTMLDivElement>(null);
+  const inputRef = useRef<HTMLTextAreaElement>(null);
+
+  useEffect(() => {
+    if (!sessionId) return;
+    setMessages([]);
+    setError(null);
+    fetchMessages(sessionId)
+      .then((msgs) => setMessages(msgs))
+      .catch((e) => setError(e?.message || 'Failed to load messages'));
+  }, [sessionId]);
+
+  useEffect(() => {
+    if (scrollRef.current) {
+      scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
+    }
+  }, [messages, streamingContent]);
+
+  const handleSend = async () => {
+    const content = input.trim();
+    if (!content || isStreaming) return;
+
+    setInput('');
+    setIsStreaming(true);
+    setStreamingContent('');
+    setToolStatus(null);
+    setError(null);
+
+    const userMsg: ChatMessage = {
+      id: 'temp-' + Date.now(),
+      session_id: sessionId,
+      role: 'user',
+      content,
+      tokens: 0,
+      model_used: '',
+    };
+    setMessages((prev) => [...prev, userMsg]);
+
+    try {
+      const stream = streamChat(sessionId, content, agentId || undefined);
+      let accumulated = '';
+
+      for await (const event of stream) {
+        if (event.type === 'token' && event.content) {
+          accumulated += event.content;
+          setStreamingContent(accumulated);
+        } else if (event.type === 'tool_calls' && event.tools) {
+          setToolStatus(`Tools: ${event.tools.join(', ')}`);
+        } else if (event.type === 'tool_result' && event.tool) {
+          setToolStatus(`Tool '${event.tool}' ausgefuehrt`);
+        } else if (event.type === 'done') {
+          setToolStatus(null);
+          const msgs = await fetchMessages(sessionId);
+          setMessages(msgs);
+          setStreamingContent('');
+        } else if (event.type === 'error') {
+          setError(event.content || 'Unknown error');
+        }
+      }
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Stream failed');
+    } finally {
+      setIsStreaming(false);
+      setStreamingContent('');
+      setToolStatus(null);
+      inputRef.current?.focus();
+    }
+  };
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Enter' && !e.shiftKey) {
+      e.preventDefault();
+      handleSend();
+    }
+  };
+
+  return (
+    <div className={clsx('flex flex-col h-full bg-white', className)}>
+      <div ref={scrollRef} className={clsx('flex-1 overflow-y-auto', compact ? 'p-3' : 'p-6')}>
+        {messages.length === 0 && !streamingContent && !error && (
+          <div className="flex items-center justify-center h-full text-secondary-400 text-sm">
+            Starte eine Konversation...
+          </div>
+        )}
+        {messages.map((msg) => (
+          <div key={msg.id} className={clsx('mb-4 flex', msg.role === 'user' ? 'justify-end' : 'justify-start')}>
+            <div className={clsx('max-w-[80%] rounded-lg px-4 py-2 text-sm', msg.role === 'user' ? 'bg-primary-600 text-white' : 'bg-secondary-100 text-secondary-900')}>
+              <div className="whitespace-pre-wrap break-words">{msg.content}</div>
+              {msg.tool_calls && msg.tool_calls.length > 0 && (
+                <div className="mt-2 text-xs opacity-70">
+                  Tools: {msg.tool_calls.map((tc: any) => tc.function?.name).join(', ')}
+                </div>
+              )}
+            </div>
+          </div>
+        ))}
+        {streamingContent && (
+          <div className="mb-4 flex justify-start">
+            <div className="max-w-[80%] rounded-lg px-4 py-2 text-sm bg-secondary-100 text-secondary-900">
+              <div className="whitespace-pre-wrap break-words">{streamingContent}</div>
+            </div>
+          </div>
+        )}
+        {toolStatus && (
+          <div className="mb-2 text-center text-xs text-secondary-500">⚙️ {toolStatus}</div>
+        )}
+        {error && (
+          <div className="mb-4 flex justify-center">
+            <div className="rounded-lg px-4 py-2 text-sm bg-red-50 text-red-700">{error}</div>
+          </div>
+        )}
+      </div>
+      <div className={clsx('border-t border-secondary-200', compact ? 'p-2' : 'p-4')}>
+        <div className="flex items-end gap-2">
+          <textarea
+            ref={inputRef}
+            value={input}
+            onChange={(e) => setInput(e.target.value)}
+            onKeyDown={handleKeyDown}
+            disabled={isStreaming}
+            placeholder="Nachricht eingeben..."
+            rows={compact ? 1 : 2}
+            className={clsx('flex-1 resize-none rounded-lg border border-secondary-300 px-3 py-2 text-sm', 'focus:outline-none focus:ring-2 focus:ring-primary-500', 'disabled:opacity-50')}
+          />
+          <button
+            onClick={handleSend}
+            disabled={isStreaming || !input.trim()}
+            className={clsx('rounded-lg px-4 py-2 text-sm font-medium text-white', 'bg-primary-600 hover:bg-primary-700', 'disabled:opacity-50 disabled:cursor-not-allowed')}
+          >
+            {isStreaming ? '...' : 'Senden'}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/components/ai/SessionList.tsx b/frontend/src/components/ai/SessionList.tsx
new file mode 100644
index 0000000..0fa8d23
--- /dev/null
+++ b/frontend/src/components/ai/SessionList.tsx
@@ -0,0 +1,103 @@
+import React, { useEffect, useState } from 'react';
+import clsx from 'clsx';
+import { fetchSessions, createSession, deleteSession, updateSession, type ChatSession } from '@/api/ai';
+
+interface SessionListProps {
+  activeSessionId: string | null;
+  onSelectSession: (id: string) => void;
+  isSidebar?: boolean;
+  className?: string;
+}
+
+export function SessionList({ activeSessionId, onSelectSession, isSidebar, className }: SessionListProps) {
+  const [sessions, setSessions] = useState<ChatSession[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  const loadSessions = async () => {
+    try {
+      setLoading(true);
+      const data = await fetchSessions(isSidebar ? true : undefined);
+      setSessions(data);
+      setError(null);
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Failed to load sessions');
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  useEffect(() => {
+    loadSessions();
+  }, [isSidebar]);
+
+  const handleNewChat = async () => {
+    try {
+      const session = await createSession({ is_sidebar: isSidebar || false });
+      setSessions((prev) => [session, ...prev]);
+      onSelectSession(session.id);
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Failed to create session');
+    }
+  };
+
+  const handleDelete = async (id: string, e: React.MouseEvent) => {
+    e.stopPropagation();
+    try {
+      await deleteSession(id);
+      setSessions((prev) => prev.filter((s) => s.id !== id));
+      if (activeSessionId === id) {
+        onSelectSession('');
+      }
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Failed to delete session');
+    }
+  };
+
+  if (loading) {
+    return <div className="p-4 text-sm text-secondary-400">Laden...</div>;
+  }
+
+  return (
+    <div className={clsx('flex flex-col h-full', className)}>
+      <div className="p-3 border-b border-secondary-200">
+        <button
+          onClick={handleNewChat}
+          className="w-full rounded-lg bg-primary-600 text-white px-3 py-2 text-sm font-medium hover:bg-primary-700"
+        >
+          + Neuer Chat
+        </button>
+      </div>
+      {error && <div className="p-2 text-xs text-red-600">{error}</div>}
+      <div className="flex-1 overflow-y-auto">
+        {sessions.length === 0 ? (
+          <div className="p-4 text-sm text-secondary-400 text-center">Keine Chats vorhanden</div>
+        ) : (
+          <ul className="space-y-1 p-2">
+            {sessions.map((session) => (
+              <li key={session.id}>
+                <div
+                  onClick={() => onSelectSession(session.id)}
+                  className={clsx(
+                    'group flex items-center gap-2 rounded-lg px-3 py-2 text-sm cursor-pointer',
+                    'hover:bg-secondary-100',
+                    activeSessionId === session.id && 'bg-primary-100 text-primary-700'
+                  )}
+                >
+                  <span className="flex-1 truncate">{session.title}</span>
+                  <button
+                    onClick={(e) => handleDelete(session.id, e)}
+                    className="opacity-0 group-hover:opacity-100 text-secondary-400 hover:text-red-600"
+                    title="Loeschen"
+                  >
+                    ✕
+                  </button>
+                </div>
+              </li>
+            ))}
+          </ul>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/components/layout/AISidebar.tsx b/frontend/src/components/layout/AISidebar.tsx
new file mode 100644
index 0000000..0e9447f
--- /dev/null
+++ b/frontend/src/components/layout/AISidebar.tsx
@@ -0,0 +1,55 @@
+import React, { useState, useEffect } from 'react';
+import { ChatWindow } from '@/components/ai/ChatWindow';
+import { createSession, fetchSessions } from '@/api/ai';
+import { useUIStore } from '@/store/uiStore';
+
+export function AISidebar() {
+  const { setAISidebarOpen } = useUIStore();
+  const [sessionId, setSessionId] = useState<string | null>(null);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    // Find or create a sidebar session
+    (async () => {
+      try {
+        const sessions = await fetchSessions(true);
+        if (sessions.length > 0) {
+          setSessionId(sessions[0].id);
+        } else {
+          const session = await createSession({ is_sidebar: true, title: 'Sidebar Chat' });
+          setSessionId(session.id);
+        }
+      } catch (e) {
+        console.error('AISidebar init error:', e);
+      } finally {
+        setLoading(false);
+      }
+    })();
+  }, []);
+
+  return (
+    <div className="w-80 flex-shrink-0 border-l border-secondary-200 bg-white flex flex-col h-full">
+      <div className="h-12 flex items-center justify-between px-3 border-b border-secondary-200">
+        <span className="text-sm font-medium text-secondary-700">KI Assistent</span>
+        <button
+          onClick={() => setAISidebarOpen(false)}
+          className="text-secondary-400 hover:text-secondary-600"
+          title="Schließen"
+        >
+          ✕
+        </button>
+      </div>
+      <div className="flex-1 overflow-hidden">
+        {loading ? (
+          <div className="flex items-center justify-center h-full text-sm text-secondary-400">Laden...</div>
+        ) : sessionId ? (
+          <ChatWindow sessionId={sessionId} compact className="h-full" />
+        ) : (
+          <div className="flex items-center justify-center h-full text-sm text-red-500">
+            Session konnte nicht erstellt werden
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/components/layout/AppShell.tsx b/frontend/src/components/layout/AppShell.tsx
index e262df2..70a2085 100644
--- a/frontend/src/components/layout/AppShell.tsx
+++ b/frontend/src/components/layout/AppShell.tsx
@@ -1,26 +1,37 @@
 import React from 'react';
-import { Outlet } from 'react-router-dom';
+import { Outlet, useLocation } from 'react-router-dom';
 import { Sidebar } from './Sidebar';
 import { TopBar } from './TopBar';
 import { PluginToolbar } from './PluginToolbar';
+import { AISidebar } from './AISidebar';
 import { ToastContainer } from '@/components/ui/Toast';
+import { useUIStore } from '@/store/uiStore';
 
 export function AppShell() {
+  const { aiSidebarOpen } = useUIStore();
+  const location = useLocation();
+
+  // Hide AI sidebar on the AI Assistant page itself
+  const showAISidebar = aiSidebarOpen && !location.pathname.startsWith('/ai-assistant');
+
   return (
     <div className="flex h-screen overflow-hidden bg-secondary-50" data-testid="app-shell">
       <Sidebar />
       <div className="flex-1 flex flex-col overflow-hidden">
         <TopBar />
         <PluginToolbar />
-        <main
-          className="flex-1 overflow-y-auto focus:outline-none"
-          tabIndex={-1}
-          role="main"
-          id="main-content"
-          data-testid="content-area"
-        >
-          <Outlet />
-        </main>
+        <div className="flex-1 flex overflow-hidden">
+          <main
+            className="flex-1 overflow-y-auto focus:outline-none"
+            tabIndex={-1}
+            role="main"
+            id="main-content"
+            data-testid="content-area"
+          >
+            <Outlet />
+          </main>
+          {showAISidebar && <AISidebar />}
+        </div>
       </div>
       <ToastContainer />
     </div>
diff --git a/frontend/src/components/layout/Sidebar.tsx b/frontend/src/components/layout/Sidebar.tsx
index 237059a..a7a5fec 100644
--- a/frontend/src/components/layout/Sidebar.tsx
+++ b/frontend/src/components/layout/Sidebar.tsx
@@ -23,6 +23,7 @@ const navItems: NavItem[] = [
   { to: '/calendar', labelKey: 'nav.calendar', icon: navIcon('M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v12a2 2 0 002 2z') },
   { to: '/dms', labelKey: 'nav.files', icon: navIcon('M7 21h10a2 2 0 002-2V9.414a1 1 0 00-.293-.707l-5.414-5.414A1 1 0 0012.586 3H7a2 2 0 00-2 2v14a2 2 0 002 2z') },
   { to: '/mail', labelKey: 'nav.email', icon: navIcon('M3 8l7.89 5.26a2 2 0 002.22 0L21 8M5 19h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z') },
+  { to: '/ai-assistant', labelKey: 'nav.aiAssistant', icon: navIcon('M9.75 17L9 20l-1 1h8l-1-1-.75-3M3 13h18M5 17h14a2 2 0 002-2V5a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z') },
   { to: '/audit-log', labelKey: 'nav.auditLog', icon: navIcon('M9 12h6m-6 4h6m2 5H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z') },
 ];
 
diff --git a/frontend/src/components/layout/TopBar.tsx b/frontend/src/components/layout/TopBar.tsx
index 0ac9ea7..f4868ad 100644
--- a/frontend/src/components/layout/TopBar.tsx
+++ b/frontend/src/components/layout/TopBar.tsx
@@ -14,7 +14,7 @@ export function TopBar() {
   const { t } = useTranslation();
   const navigate = useNavigate();
   const { user } = useAuthStore();
-  const { toggleSidebar } = useUIStore();
+  const { toggleSidebar, toggleAISidebar } = useUIStore();
   const { currentTenant, availableTenants, switchTenant, isSwitching } = useTenant();
   const logoutMutation = useLogout();
 
@@ -69,6 +69,18 @@ export function TopBar() {
           </svg>
         </button>
 
+        {/* AI Assistant toggle */}
+        <button
+          onClick={toggleAISidebar}
+          className="p-2 rounded-md hover:bg-secondary-100 min-h-touch min-w-touch flex items-center justify-center focus:outline-none focus-visible:ring-2 focus-visible:ring-primary-500"
+          aria-label="KI Assistent"
+          title="KI Assistent"
+        >
+          <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
+            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9.75 17L9 20l-1 1h8l-1-1-.75-3M3 13h18M5 17h14a2 2 0 002-2V5a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z" />
+          </svg>
+        </button>
+
         {/* Tenant switcher */}
         <div ref={tenantRef} className="relative">
           <button
diff --git a/frontend/src/i18n/locales/de.json b/frontend/src/i18n/locales/de.json
index 8d4f5ef..6b3f92d 100644
--- a/frontend/src/i18n/locales/de.json
+++ b/frontend/src/i18n/locales/de.json
@@ -12,7 +12,8 @@
     "email": "E-Mail",
     "users": "Benutzer",
     "auditLog": "Audit-Log",
-    "settings": "Einstellungen"
+    "settings": "Einstellungen",
+    "aiAssistant": "KI Assistent"
   },
   "auth": {
     "login": "Anmelden",
@@ -575,4 +576,4 @@
       "general": "Allgemein"
     }
   }
-}
+}
\ No newline at end of file
diff --git a/frontend/src/i18n/locales/en.json b/frontend/src/i18n/locales/en.json
index bc3a391..1bb471d 100644
--- a/frontend/src/i18n/locales/en.json
+++ b/frontend/src/i18n/locales/en.json
@@ -12,7 +12,8 @@
     "email": "Email",
     "users": "Users",
     "auditLog": "Audit Log",
-    "settings": "Settings"
+    "settings": "Settings",
+    "aiAssistant": "AI Assistant"
   },
   "auth": {
     "login": "Sign In",
@@ -575,4 +576,4 @@
       "general": "General"
     }
   }
-}
+}
\ No newline at end of file
diff --git a/frontend/src/pages/AIAssistant.tsx b/frontend/src/pages/AIAssistant.tsx
new file mode 100644
index 0000000..a567a00
--- /dev/null
+++ b/frontend/src/pages/AIAssistant.tsx
@@ -0,0 +1,36 @@
+import React, { useState } from 'react';
+import { SessionList } from '@/components/ai/SessionList';
+import { ChatWindow } from '@/components/ai/ChatWindow';
+
+export function AIAssistantPage() {
+  const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
+
+  return (
+    <div className="flex h-full" data-testid="ai-assistant-page">
+      {/* Left: Session List */}
+      <div className="w-72 flex-shrink-0 border-r border-secondary-200 bg-white">
+        <div className="h-16 flex items-center px-6 border-b border-secondary-200">
+          <h1 className="text-lg font-bold text-secondary-900">KI Assistent</h1>
+        </div>
+        <SessionList
+          activeSessionId={activeSessionId}
+          onSelectSession={setActiveSessionId}
+          className="h-[calc(100%-4rem)]"
+        />
+      </div>
+      {/* Right: Chat Window */}
+      <div className="flex-1 flex flex-col">
+        {activeSessionId ? (
+          <ChatWindow sessionId={activeSessionId} className="flex-1" />
+        ) : (
+          <div className="flex-1 flex items-center justify-center text-secondary-400">
+            <div className="text-center">
+              <div className="text-4xl mb-3">🤖</div>
+              <div className="text-sm">Wähle einen Chat oder erstelle einen neuen</div>
+            </div>
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/pages/AISettings.tsx b/frontend/src/pages/AISettings.tsx
new file mode 100644
index 0000000..ef09808
--- /dev/null
+++ b/frontend/src/pages/AISettings.tsx
@@ -0,0 +1,332 @@
+import React, { useState, useEffect } from 'react';
+import { Tabs } from '@/components/shared/Tabs';
+import {
+  fetchProviders, createProvider, updateProvider, deleteProvider,
+  fetchPresets, createPreset, updatePreset, deletePreset,
+  fetchAgents, createAgent, updateAgent, deleteAgent,
+  fetchTools,
+  type AIProvider, type AIPreset, type AIAgent, type AITool,
+} from '@/api/ai';
+
+// ─── Provider Tab ───
+function ProviderTab() {
+  const [providers, setProviders] = useState<AIProvider[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [showForm, setShowForm] = useState(false);
+  const [editId, setEditId] = useState<string | null>(null);
+  const [form, setForm] = useState({ name: '', provider_type: 'openai', api_key: '', base_url: '', is_default: false });
+
+  const load = async () => {
+    try { setProviders(await fetchProviders()); } catch (e: any) { setError(e?.message); } finally { setLoading(false); }
+  };
+  useEffect(() => { load(); }, []);
+
+  const handleSave = async () => {
+    try {
+      if (editId) { await updateProvider(editId, form); } else { await createProvider(form); }
+      setShowForm(false); setEditId(null); setForm({ name: '', provider_type: 'openai', api_key: '', base_url: '', is_default: false });
+      await load();
+    } catch (e: any) { setError(e?.message); }
+  };
+
+  const handleEdit = (p: AIProvider) => {
+    setEditId(p.id); setForm({ name: p.name, provider_type: p.provider_type, api_key: '', base_url: p.base_url, is_default: p.is_default });
+    setShowForm(true);
+  };
+
+  const handleDelete = async (id: string) => {
+    if (!confirm('Anbieter wirklich löschen?')) return;
+    try { await deleteProvider(id); await load(); } catch (e: any) { setError(e?.message); }
+  };
+
+  if (loading) return <div className="p-4">Laden...</div>;
+
+  return (
+    <div className="space-y-4">
+      <div className="flex justify-between items-center">
+        <h2 className="text-lg font-semibold">Anbieter</h2>
+        <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', provider_type: 'openai', api_key: '', base_url: '', is_default: false }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg hover:bg-primary-700">+ Hinzufügen</button>
+      </div>
+      {error && <div className="text-sm text-red-600">{error}</div>}
+      {showForm && (
+        <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
+          <div className="grid grid-cols-2 gap-3">
+            <input placeholder="Name" value={form.name} onChange={(e) => setForm({ ...form, name: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+            <select value={form.provider_type} onChange={(e) => setForm({ ...form, provider_type: e.target.value })} className="border rounded-lg px-3 py-2 text-sm">
+              <option value="openai">OpenAI</option>
+              <option value="anthropic">Anthropic</option>
+              <option value="ollama">Ollama</option>
+              <option value="azure">Azure OpenAI</option>
+              <option value="huggingface">HuggingFace</option>
+              <option value="custom">Custom</option>
+            </select>
+            <input placeholder="API Key" type="password" value={form.api_key} onChange={(e) => setForm({ ...form, api_key: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+            <input placeholder="Base URL (optional)" value={form.base_url} onChange={(e) => setForm({ ...form, base_url: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+          </div>
+          <label className="flex items-center gap-2 text-sm">
+            <input type="checkbox" checked={form.is_default} onChange={(e) => setForm({ ...form, is_default: e.target.checked })} /> Standard-Anbieter
+          </label>
+          <div className="flex gap-2">
+            <button onClick={handleSave} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">Speichern</button>
+            <button onClick={() => setShowForm(false)} className="px-3 py-1.5 text-sm border rounded-lg">Abbrechen</button>
+          </div>
+        </div>
+      )}
+      <div className="space-y-2">
+        {providers.map((p) => (
+          <div key={p.id} className="border border-secondary-200 rounded-lg p-3 flex items-center justify-between">
+            <div>
+              <div className="font-medium text-sm">{p.name} {p.is_default && <span className="text-xs text-primary-600">(Standard)</span>}</div>
+              <div className="text-xs text-secondary-500">{p.provider_type} · {p.api_key}</div>
+            </div>
+            <div className="flex gap-2">
+              <button onClick={() => handleEdit(p)} className="text-sm text-primary-600 hover:underline">Bearbeiten</button>
+              <button onClick={() => handleDelete(p.id)} className="text-sm text-red-600 hover:underline">Löschen</button>
+            </div>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+// ─── Presets Tab ───
+function PresetTab() {
+  const [presets, setPresets] = useState<AIPreset[]>([]);
+  const [providers, setProviders] = useState<AIProvider[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [showForm, setShowForm] = useState(false);
+  const [editId, setEditId] = useState<string | null>(null);
+  const [form, setForm] = useState({ name: '', model_id: '', provider_id: '', temperature: 0.7, max_tokens: 2048, top_p: 1.0, system_prompt: '' });
+
+  const load = async () => {
+    try { setPresets(await fetchPresets()); setProviders(await fetchProviders()); } catch (e: any) { setError(e?.message); } finally { setLoading(false); }
+  };
+  useEffect(() => { load(); }, []);
+
+  const handleSave = async () => {
+    try {
+      const data = { ...form, provider_id: form.provider_id || undefined };
+      if (editId) { await updatePreset(editId, data); } else { await createPreset(data); }
+      setShowForm(false); setEditId(null); setForm({ name: '', model_id: '', provider_id: '', temperature: 0.7, max_tokens: 2048, top_p: 1.0, system_prompt: '' });
+      await load();
+    } catch (e: any) { setError(e?.message); }
+  };
+
+  const handleEdit = (p: AIPreset) => {
+    setEditId(p.id); setForm({ name: p.name, model_id: p.model_id, provider_id: p.provider_id || '', temperature: p.temperature, max_tokens: p.max_tokens, top_p: p.top_p, system_prompt: p.system_prompt });
+    setShowForm(true);
+  };
+
+  const handleDelete = async (id: string) => {
+    if (!confirm('Preset löschen?')) return;
+    try { await deletePreset(id); await load(); } catch (e: any) { setError(e?.message); }
+  };
+
+  if (loading) return <div className="p-4">Laden...</div>;
+
+  return (
+    <div className="space-y-4">
+      <div className="flex justify-between items-center">
+        <h2 className="text-lg font-semibold">Modelle & Presets</h2>
+        <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', model_id: '', provider_id: '', temperature: 0.7, max_tokens: 2048, top_p: 1.0, system_prompt: '' }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">+ Hinzufügen</button>
+      </div>
+      {error && <div className="text-sm text-red-600">{error}</div>}
+      {showForm && (
+        <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
+          <div className="grid grid-cols-2 gap-3">
+            <input placeholder="Preset Name" value={form.name} onChange={(e) => setForm({ ...form, name: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+            <input placeholder="Modell ID (z.B. gpt-4o-mini)" value={form.model_id} onChange={(e) => setForm({ ...form, model_id: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+            <select value={form.provider_id} onChange={(e) => setForm({ ...form, provider_id: e.target.value })} className="border rounded-lg px-3 py-2 text-sm">
+              <option value="">Anbieter wählen...</option>
+              {providers.map((p) => <option key={p.id} value={p.id}>{p.name}</option>)}
+            </select>
+            <input type="number" step="0.1" min="0" max="2" placeholder="Temperature" value={form.temperature} onChange={(e) => setForm({ ...form, temperature: parseFloat(e.target.value) })} className="border rounded-lg px-3 py-2 text-sm" />
+            <input type="number" placeholder="Max Tokens" value={form.max_tokens} onChange={(e) => setForm({ ...form, max_tokens: parseInt(e.target.value) })} className="border rounded-lg px-3 py-2 text-sm" />
+            <input type="number" step="0.1" min="0" max="1" placeholder="Top P" value={form.top_p} onChange={(e) => setForm({ ...form, top_p: parseFloat(e.target.value) })} className="border rounded-lg px-3 py-2 text-sm" />
+          </div>
+          <textarea placeholder="System Prompt (optional)" value={form.system_prompt} onChange={(e) => setForm({ ...form, system_prompt: e.target.value })} rows={3} className="w-full border rounded-lg px-3 py-2 text-sm" />
+          <div className="flex gap-2">
+            <button onClick={handleSave} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">Speichern</button>
+            <button onClick={() => setShowForm(false)} className="px-3 py-1.5 text-sm border rounded-lg">Abbrechen</button>
+          </div>
+        </div>
+      )}
+      <div className="space-y-2">
+        {presets.map((p) => (
+          <div key={p.id} className="border border-secondary-200 rounded-lg p-3 flex items-center justify-between">
+            <div>
+              <div className="font-medium text-sm">{p.name}</div>
+              <div className="text-xs text-secondary-500">{p.model_id} · temp={p.temperature} · max_tokens={p.max_tokens}</div>
+            </div>
+            <div className="flex gap-2">
+              <button onClick={() => handleEdit(p)} className="text-sm text-primary-600 hover:underline">Bearbeiten</button>
+              <button onClick={() => handleDelete(p.id)} className="text-sm text-red-600 hover:underline">Löschen</button>
+            </div>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+// ─── Agents Tab ───
+function AgentTab() {
+  const [agents, setAgents] = useState<AIAgent[]>([]);
+  const [presets, setPresets] = useState<AIPreset[]>([]);
+  const [tools, setTools] = useState<AITool[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [showForm, setShowForm] = useState(false);
+  const [editId, setEditId] = useState<string | null>(null);
+  const [form, setForm] = useState({ name: '', description: '', system_prompt: '', preset_id: '', tool_ids: [] as string[] });
+
+  const load = async () => {
+    try { setAgents(await fetchAgents()); setPresets(await fetchPresets()); setTools(await fetchTools()); } catch (e: any) { setError(e?.message); } finally { setLoading(false); }
+  };
+  useEffect(() => { load(); }, []);
+
+  const handleSave = async () => {
+    try {
+      const data = { ...form, preset_id: form.preset_id || undefined };
+      if (editId) { await updateAgent(editId, data); } else { await createAgent(data); }
+      setShowForm(false); setEditId(null); setForm({ name: '', description: '', system_prompt: '', preset_id: '', tool_ids: [] });
+      await load();
+    } catch (e: any) { setError(e?.message); }
+  };
+
+  const handleEdit = (a: AIAgent) => {
+    setEditId(a.id); setForm({ name: a.name, description: a.description, system_prompt: a.system_prompt, preset_id: a.preset_id || '', tool_ids: a.tool_ids || [] });
+    setShowForm(true);
+  };
+
+  const handleDelete = async (id: string) => {
+    if (!confirm('Agent löschen?')) return;
+    try { await deleteAgent(id); await load(); } catch (e: any) { setError(e?.message); }
+  };
+
+  const toggleTool = (toolName: string) => {
+    setForm((prev) => ({
+      ...prev,
+      tool_ids: prev.tool_ids.includes(toolName)
+        ? prev.tool_ids.filter((t) => t !== toolName)
+        : [...prev.tool_ids, toolName],
+    }));
+  };
+
+  if (loading) return <div className="p-4">Laden...</div>;
+
+  return (
+    <div className="space-y-4">
+      <div className="flex justify-between items-center">
+        <h2 className="text-lg font-semibold">Agenten</h2>
+        <button onClick={() => { setShowForm(!showForm); setEditId(null); setForm({ name: '', description: '', system_prompt: '', preset_id: '', tool_ids: [] }); }} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">+ Hinzufügen</button>
+      </div>
+      {error && <div className="text-sm text-red-600">{error}</div>}
+      {showForm && (
+        <div className="border border-secondary-200 rounded-lg p-4 space-y-3 bg-secondary-50">
+          <div className="grid grid-cols-2 gap-3">
+            <input placeholder="Name" value={form.name} onChange={(e) => setForm({ ...form, name: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+            <input placeholder="Beschreibung" value={form.description} onChange={(e) => setForm({ ...form, description: e.target.value })} className="border rounded-lg px-3 py-2 text-sm" />
+          </div>
+          <select value={form.preset_id} onChange={(e) => setForm({ ...form, preset_id: e.target.value })} className="w-full border rounded-lg px-3 py-2 text-sm">
+            <option value="">Preset wählen...</option>
+            {presets.map((p) => <option key={p.id} value={p.id}>{p.name} ({p.model_id})</option>)}
+          </select>
+          <textarea placeholder="System Prompt" value={form.system_prompt} onChange={(e) => setForm({ ...form, system_prompt: e.target.value })} rows={4} className="w-full border rounded-lg px-3 py-2 text-sm" />
+          {tools.length > 0 && (
+            <div>
+              <div className="text-sm font-medium mb-2">Tools:</div>
+              <div className="space-y-1 max-h-40 overflow-y-auto">
+                {tools.map((tool) => (
+                  <label key={tool.name} className="flex items-center gap-2 text-sm">
+                    <input type="checkbox" checked={form.tool_ids.includes(tool.name)} onChange={() => toggleTool(tool.name)} />
+                    <span>{tool.name} <span className="text-xs text-secondary-400">({tool.plugin_name})</span></span>
+                  </label>
+                ))}
+              </div>
+            </div>
+          )}
+          <div className="flex gap-2">
+            <button onClick={handleSave} className="px-3 py-1.5 text-sm bg-primary-600 text-white rounded-lg">Speichern</button>
+            <button onClick={() => setShowForm(false)} className="px-3 py-1.5 text-sm border rounded-lg">Abbrechen</button>
+          </div>
+        </div>
+      )}
+      <div className="space-y-2">
+        {agents.map((a) => (
+          <div key={a.id} className="border border-secondary-200 rounded-lg p-3 flex items-center justify-between">
+            <div>
+              <div className="font-medium text-sm">{a.name} {a.is_default && <span className="text-xs text-primary-600">(Standard)</span>}</div>
+              <div className="text-xs text-secondary-500">{a.description || 'Keine Beschreibung'}</div>
+              {a.tool_ids.length > 0 && <div className="text-xs text-secondary-400 mt-1">Tools: {a.tool_ids.join(', ')}</div>}
+            </div>
+            <div className="flex gap-2">
+              <button onClick={() => handleEdit(a)} className="text-sm text-primary-600 hover:underline">Bearbeiten</button>
+              {!a.is_default && <button onClick={() => handleDelete(a.id)} className="text-sm text-red-600 hover:underline">Löschen</button>}
+            </div>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+// ─── Tools Tab ───
+function ToolsTab() {
+  const [tools, setTools] = useState<AITool[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    fetchTools().then(setTools).catch((e) => setError(e?.message)).finally(() => setLoading(false));
+  }, []);
+
+  if (loading) return <div className="p-4">Laden...</div>;
+
+  return (
+    <div className="space-y-4">
+      <h2 className="text-lg font-semibold">Verfügbare Tools</h2>
+      <p className="text-sm text-secondary-500">Diese Tools werden von Plugins bereitgestellt und können Agenten zugewiesen werden.</p>
+      {error && <div className="text-sm text-red-600">{error}</div>}
+      {tools.length === 0 ? (
+        <div className="text-sm text-secondary-400 py-8 text-center">Keine Tools verfügbar. Plugins können Tools registrieren.</div>
+      ) : (
+        <div className="space-y-2">
+          {tools.map((tool) => (
+            <div key={tool.name} className="border border-secondary-200 rounded-lg p-3">
+              <div className="flex items-center justify-between">
+                <div className="font-medium text-sm">{tool.name}</div>
+                <div className="flex gap-2 text-xs">
+                  {tool.required_permission && <span className="px-2 py-0.5 rounded bg-amber-100 text-amber-700">{tool.required_permission}</span>}
+                  <span className="px-2 py-0.5 rounded bg-secondary-100 text-secondary-600">{tool.plugin_name}</span>
+                  <span className="px-2 py-0.5 rounded bg-secondary-100 text-secondary-600">{tool.category}</span>
+                </div>
+              </div>
+              <div className="text-xs text-secondary-500 mt-1">{tool.description}</div>
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  );
+}
+
+// ─── Main Settings Page ───
+export function AISettingsPage() {
+  const tabs = [
+    { key: 'providers', label: 'Anbieter', content: <ProviderTab /> },
+    { key: 'presets', label: 'Modelle & Presets', content: <PresetTab /> },
+    { key: 'agents', label: 'Agenten', content: <AgentTab /> },
+    { key: 'tools', label: 'Tools', content: <ToolsTab /> },
+  ];
+
+  return (
+    <div className="max-w-4xl">
+      <h1 className="text-2xl font-bold text-secondary-900 mb-6">KI Assistent Einstellungen</h1>
+      <Tabs tabs={tabs} />
+    </div>
+  );
+}
diff --git a/frontend/src/pages/Settings.tsx b/frontend/src/pages/Settings.tsx
index f3eab19..d858cf1 100644
--- a/frontend/src/pages/Settings.tsx
+++ b/frontend/src/pages/Settings.tsx
@@ -16,6 +16,7 @@ export function SettingsPage() {
     { to: '/settings/taxes', label: t('taxes.title'), icon: '\ud83d\udccb' },
     { to: '/settings/sequences', label: t('sequences.title'), icon: '\ud83d\udd22' },
     { to: '/settings/mail', label: t('mail.settings'), icon: '\ud83d\udce7' },
+    { to: '/settings/ai', label: t('nav.aiAssistant'), icon: '\ud83e\udde0' },
     { to: '/settings/notifications', label: t('settings.notifications'), icon: '\ud83d\udd14' },
   ];
 
diff --git a/frontend/src/routes/index.tsx b/frontend/src/routes/index.tsx
index 8304d00..624d227 100644
--- a/frontend/src/routes/index.tsx
+++ b/frontend/src/routes/index.tsx
@@ -31,6 +31,8 @@ import { DmsTrashPage } from '@/pages/DmsTrash';
 import { MailPage } from '@/pages/Mail';
 import { MailSettingsPage } from '@/pages/MailSettings';
 import { SettingsNotificationsPage } from '@/pages/SettingsNotifications';
+import { AIAssistantPage } from '@/pages/AIAssistant';
+import { AISettingsPage } from '@/pages/AISettings';
 
 const router = createBrowserRouter([
   {
@@ -70,6 +72,7 @@ const router = createBrowserRouter([
       { path: '/dms/trash', element: <DmsTrashPage /> },
       { path: '/mail', element: <MailPage /> },
       { path: '/mail/settings', element: <MailSettingsPage /> },
+      { path: '/ai-assistant', element: <AIAssistantPage /> },
       {
         path: '/settings',
         element: <SettingsPage />,
@@ -85,6 +88,7 @@ const router = createBrowserRouter([
           { path: 'sequences', element: <SettingsSequencesPage /> },
           { path: 'mail', element: <MailSettingsPage /> },
           { path: 'notifications', element: <SettingsNotificationsPage /> },
+          { path: 'ai', element: <AISettingsPage /> },
         ],
       },
     ],
diff --git a/frontend/src/store/uiStore.ts b/frontend/src/store/uiStore.ts
index 724ca67..8ad35cb 100644
--- a/frontend/src/store/uiStore.ts
+++ b/frontend/src/store/uiStore.ts
@@ -14,11 +14,14 @@ export interface UIState {
   theme: Theme;
   locale: Locale;
   sidebarOpen: boolean;
+  aiSidebarOpen: boolean;
   toasts: Toast[];
   setTheme: (theme: Theme) => void;
   setLocale: (locale: Locale) => void;
   toggleSidebar: () => void;
   setSidebarOpen: (open: boolean) => void;
+  toggleAISidebar: () => void;
+  setAISidebarOpen: (open: boolean) => void;
   addToast: (toast: Omit<Toast, 'id'>) => void;
   removeToast: (id: string) => void;
   clearToasts: () => void;
@@ -30,6 +33,7 @@ export const useUIStore = create<UIState>((set) => ({
   theme: (localStorage.getItem('leocrm_theme') as Theme) || 'light',
   locale: (localStorage.getItem('leocrm_lang') as Locale) || 'de',
   sidebarOpen: true,
+  aiSidebarOpen: false,
   toasts: [],
   setTheme: (theme) => {
     localStorage.setItem('leocrm_theme', theme);
@@ -41,6 +45,8 @@ export const useUIStore = create<UIState>((set) => ({
   },
   toggleSidebar: () => set((s) => ({ sidebarOpen: !s.sidebarOpen })),
   setSidebarOpen: (open) => set({ sidebarOpen: open }),
+  toggleAISidebar: () => set((s) => ({ aiSidebarOpen: !s.aiSidebarOpen })),
+  setAISidebarOpen: (open) => set({ aiSidebarOpen: open }),
   addToast: (toast) => {
     const id = `toast-${++toastIdCounter}`;
     set((s) => ({ toasts: [...s.toasts, { ...toast, id }] }));