diff --git a/apps/web/src/app/(dashboard)/chat/page.tsx b/apps/web/src/app/(dashboard)/chat/page.tsx
index dec3e62..8a0760b 100644
--- a/apps/web/src/app/(dashboard)/chat/page.tsx
+++ b/apps/web/src/app/(dashboard)/chat/page.tsx
@@ -1,190 +1,153 @@
 'use client';
 
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import { useCallback, useEffect, useRef, useState } from 'react';
 import { api } from '@/lib/api';
 import { destroySocket, getSocket } from '@/lib/socket';
-import type { Conversation, Message, ModelInfo, ProviderInfo } from '@/lib/types';
-import { ConversationList } from '@/components/chat/conversation-list';
+import type { Conversation, Message } from '@/lib/types';
+import {
+  ConversationSidebar,
+  type ConversationSidebarRef,
+} from '@/components/chat/conversation-sidebar';
 import { MessageBubble } from '@/components/chat/message-bubble';
 import { ChatInput } from '@/components/chat/chat-input';
 import { StreamingMessage } from '@/components/chat/streaming-message';
-import { AppHeader } from '@/components/layout/app-header';
 
-const FALLBACK_MODELS: ModelInfo[] = [
-  {
-    id: 'claude-3-5-sonnet',
-    provider: 'anthropic',
-    name: 'claude-3.5-sonnet',
-    reasoning: true,
-    contextWindow: 200_000,
-    maxTokens: 8_192,
-    inputTypes: ['text'],
-    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
-  },
-  {
-    id: 'gpt-4.1',
-    provider: 'openai',
-    name: 'gpt-4.1',
-    reasoning: false,
-    contextWindow: 128_000,
-    maxTokens: 8_192,
-    inputTypes: ['text'],
-    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
-  },
-  {
-    id: 'gemini-2.0-flash',
-    provider: 'google',
-    name: 'gemini-2.0-flash',
-    reasoning: false,
-    contextWindow: 1_000_000,
-    maxTokens: 8_192,
-    inputTypes: ['text', 'image'],
-    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
-  },
-];
+interface ModelInfo {
+  id: string;
+  provider: string;
+  name: string;
+  reasoning: boolean;
+  contextWindow: number;
+  maxTokens: number;
+  inputTypes: ('text' | 'image')[];
+  cost: { input: number; output: number; cacheRead: number; cacheWrite: number };
+}
+
+interface ProviderInfo {
+  id: string;
+  name: string;
+  available: boolean;
+  models: ModelInfo[];
+}
 
 export default function ChatPage(): React.ReactElement {
-  const [conversations, setConversations] = useState<Conversation[]>([]);
   const [activeId, setActiveId] = useState<string | null>(null);
   const [messages, setMessages] = useState<Message[]>([]);
-  const [sidebarOpen, setSidebarOpen] = useState(true);
-  const [models, setModels] = useState<ModelInfo[]>(FALLBACK_MODELS);
-  const [selectedModelId, setSelectedModelId] = useState(FALLBACK_MODELS[0]?.id ?? '');
   const [streamingText, setStreamingText] = useState('');
-  const [streamingThinking, setStreamingThinking] = useState('');
   const [isStreaming, setIsStreaming] = useState(false);
+  const [isSidebarOpen, setIsSidebarOpen] = useState(true);
+  const [models, setModels] = useState<ModelInfo[]>([]);
+  const [selectedModelId, setSelectedModelId] = useState('');
   const messagesEndRef = useRef<HTMLDivElement>(null);
-  const activeIdRef = useRef<string | null>(null);
-  const streamingTextRef = useRef('');
-  const streamingThinkingRef = useRef('');
+  const sidebarRef = useRef<ConversationSidebarRef>(null);
 
+  // Track the active conversation ID in a ref so socket event handlers always
+  // see the current value without needing to be re-registered.
+  const activeIdRef = useRef<string | null>(null);
   activeIdRef.current = activeId;
 
-  const selectedModel = useMemo(
-    () => models.find((model) => model.id === selectedModelId) ?? models[0] ?? null,
-    [models, selectedModelId],
-  );
-  const selectedModelRef = useRef<ModelInfo | null>(selectedModel);
-  selectedModelRef.current = selectedModel;
+  // Accumulate streamed text in a ref so agent:end can read the full content
+  // without stale-closure issues.
+  const streamingTextRef = useRef('');
 
   useEffect(() => {
-    api<Conversation[]>('/api/conversations')
-      .then(setConversations)
-      .catch(() => {});
+    const savedState = window.localStorage.getItem('mosaic-sidebar-open');
+    if (savedState !== null) {
+      setIsSidebarOpen(savedState === 'true');
+    }
   }, []);
 
+  useEffect(() => {
+    window.localStorage.setItem('mosaic-sidebar-open', String(isSidebarOpen));
+  }, [isSidebarOpen]);
+
   useEffect(() => {
     api<ProviderInfo[]>('/api/providers')
-      .then((providers) =>
-        providers.filter((provider) => provider.available).flatMap((provider) => provider.models),
-      )
-      .then((availableModels) => {
-        if (availableModels.length === 0) return;
+      .then((providers) => {
+        const availableModels = providers
+          .filter((provider) => provider.available)
+          .flatMap((provider) => provider.models);
         setModels(availableModels);
-        setSelectedModelId((current) =>
-          availableModels.some((model) => model.id === current) ? current : availableModels[0]!.id,
-        );
+        setSelectedModelId((current) => current || availableModels[0]?.id || '');
       })
       .catch(() => {
-        setModels(FALLBACK_MODELS);
+        setModels([]);
+        setSelectedModelId('');
       });
   }, []);
 
+  // Load messages when active conversation changes
   useEffect(() => {
     if (!activeId) {
       setMessages([]);
       return;
     }
-
+    // Clear streaming state when switching conversations
     setIsStreaming(false);
     setStreamingText('');
-    setStreamingThinking('');
     streamingTextRef.current = '';
-    streamingThinkingRef.current = '';
-
     api<Message[]>(`/api/conversations/${activeId}/messages`)
-      .then((fetchedMessages) => setMessages(fetchedMessages.map(normalizeMessage)))
+      .then(setMessages)
       .catch(() => {});
   }, [activeId]);
 
+  // Auto-scroll to bottom
   useEffect(() => {
     messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' });
-  }, [messages, streamingText, streamingThinking]);
+  }, [messages, streamingText]);
 
+  // Socket.io setup — connect once for the page lifetime
   useEffect(() => {
     const socket = getSocket();
 
     function onAgentStart(data: { conversationId: string }): void {
+      // Only update state if the event belongs to the currently viewed conversation
       if (activeIdRef.current !== data.conversationId) return;
       setIsStreaming(true);
       setStreamingText('');
-      setStreamingThinking('');
       streamingTextRef.current = '';
-      streamingThinkingRef.current = '';
     }
 
-    function onAgentText(data: { conversationId: string; text?: string; thinking?: string }): void {
+    function onAgentText(data: { conversationId: string; text: string }): void {
       if (activeIdRef.current !== data.conversationId) return;
-      if (data.text) {
-        streamingTextRef.current += data.text;
-        setStreamingText((prev) => prev + data.text);
-      }
-      if (data.thinking) {
-        streamingThinkingRef.current += data.thinking;
-        setStreamingThinking((prev) => prev + data.thinking);
-      }
+      streamingTextRef.current += data.text;
+      setStreamingText((prev) => prev + data.text);
     }
 
-    function onAgentEnd(data: {
-      conversationId: string;
-      thinking?: string;
-      model?: string;
-      provider?: string;
-      promptTokens?: number;
-      completionTokens?: number;
-      totalTokens?: number;
-    }): void {
+    function onAgentEnd(data: { conversationId: string }): void {
       if (activeIdRef.current !== data.conversationId) return;
       const finalText = streamingTextRef.current;
-      const finalThinking = data.thinking ?? streamingThinkingRef.current;
       setIsStreaming(false);
       setStreamingText('');
-      setStreamingThinking('');
       streamingTextRef.current = '';
-      streamingThinkingRef.current = '';
-
+      // Append the completed assistant message to the local message list.
+      // The Pi agent session is in-memory so the assistant response is not
+      // persisted to the DB — we build the local UI state instead.
       if (finalText) {
         setMessages((prev) => [
           ...prev,
           {
             id: `assistant-${Date.now()}`,
             conversationId: data.conversationId,
-            role: 'assistant',
+            role: 'assistant' as const,
             content: finalText,
-            thinking: finalThinking || undefined,
-            model: data.model ?? selectedModelRef.current?.name,
-            provider: data.provider ?? selectedModelRef.current?.provider,
-            promptTokens: data.promptTokens,
-            completionTokens: data.completionTokens,
-            totalTokens: data.totalTokens,
             createdAt: new Date().toISOString(),
           },
         ]);
+        sidebarRef.current?.refresh();
       }
     }
 
     function onError(data: { error: string; conversationId?: string }): void {
       setIsStreaming(false);
       setStreamingText('');
-      setStreamingThinking('');
       streamingTextRef.current = '';
-      streamingThinkingRef.current = '';
       setMessages((prev) => [
         ...prev,
         {
           id: `error-${Date.now()}`,
           conversationId: data.conversationId ?? '',
-          role: 'system',
+          role: 'system' as const,
           content: `Error: ${data.error}`,
           createdAt: new Date().toISOString(),
         },
@@ -196,6 +159,7 @@ export default function ChatPage(): React.ReactElement {
     socket.on('agent:end', onAgentEnd);
     socket.on('error', onError);
 
+    // Connect if not already connected
     if (!socket.connected) {
       socket.connect();
     }
@@ -205,263 +169,197 @@ export default function ChatPage(): React.ReactElement {
       socket.off('agent:text', onAgentText);
       socket.off('agent:end', onAgentEnd);
       socket.off('error', onError);
+      // Fully tear down the socket when the chat page unmounts so we get a
+      // fresh authenticated connection next time the page is visited.
       destroySocket();
     };
   }, []);
 
-  const handleNewConversation = useCallback(async () => {
-    const conversation = await api<Conversation>('/api/conversations', {
+  const handleNewConversation = useCallback(async (projectId?: string | null) => {
+    const conv = await api<Conversation>('/api/conversations', {
       method: 'POST',
-      body: { title: 'New conversation' },
+      body: { title: 'New conversation', projectId: projectId ?? null },
     });
-    setConversations((prev) => [conversation, ...prev]);
-    setActiveId(conversation.id);
+
+    sidebarRef.current?.addConversation({
+      id: conv.id,
+      title: conv.title,
+      projectId: conv.projectId,
+      updatedAt: conv.updatedAt,
+      archived: conv.archived,
+    });
+
+    setActiveId(conv.id);
     setMessages([]);
+    setIsSidebarOpen(true);
   }, []);
 
-  const handleRename = useCallback(async (id: string, title: string) => {
-    const updated = await api<Conversation>(`/api/conversations/${id}`, {
-      method: 'PATCH',
-      body: { title },
-    });
-    setConversations((prev) =>
-      prev.map((conversation) => (conversation.id === id ? updated : conversation)),
-    );
-  }, []);
-
-  const handleDelete = useCallback(
-    async (id: string) => {
-      try {
-        await api<void>(`/api/conversations/${id}`, { method: 'DELETE' });
-        setConversations((prev) => prev.filter((conversation) => conversation.id !== id));
-        if (activeId === id) {
-          setActiveId(null);
-          setMessages([]);
-        }
-      } catch (error) {
-        console.error('[ChatPage] Failed to delete conversation:', error);
-      }
-    },
-    [activeId],
-  );
-
-  const handleArchive = useCallback(
-    async (id: string, archived: boolean) => {
-      const updated = await api<Conversation>(`/api/conversations/${id}`, {
-        method: 'PATCH',
-        body: { archived },
-      });
-      setConversations((prev) =>
-        prev.map((conversation) => (conversation.id === id ? updated : conversation)),
-      );
-      if (archived && activeId === id) {
-        setActiveId(null);
-        setMessages([]);
-      }
-    },
-    [activeId],
-  );
-
   const handleSend = useCallback(
     async (content: string, options?: { modelId?: string }) => {
-      let conversationId = activeId;
+      let convId = activeId;
 
-      if (!conversationId) {
+      // Auto-create conversation if none selected
+      if (!convId) {
         const autoTitle = content.slice(0, 60);
-        const conversation = await api<Conversation>('/api/conversations', {
+        const conv = await api<Conversation>('/api/conversations', {
           method: 'POST',
           body: { title: autoTitle },
         });
-        setConversations((prev) => [conversation, ...prev]);
-        setActiveId(conversation.id);
-        conversationId = conversation.id;
-      } else {
-        const activeConversation = conversations.find(
-          (conversation) => conversation.id === conversationId,
-        );
-        if (activeConversation?.title === 'New conversation' && messages.length === 0) {
-          const autoTitle = content.slice(0, 60);
-          api<Conversation>(`/api/conversations/${conversationId}`, {
-            method: 'PATCH',
-            body: { title: autoTitle },
-          })
-            .then((updated) => {
-              setConversations((prev) =>
-                prev.map((conversation) =>
-                  conversation.id === conversationId ? updated : conversation,
-                ),
-              );
-            })
-            .catch(() => {});
-        }
+        sidebarRef.current?.addConversation({
+          id: conv.id,
+          title: conv.title,
+          projectId: conv.projectId,
+          updatedAt: conv.updatedAt,
+          archived: conv.archived,
+        });
+        setActiveId(conv.id);
+        convId = conv.id;
+      } else if (messages.length === 0) {
+        // Auto-title the initial placeholder conversation from the first user message.
+        const autoTitle = content.slice(0, 60);
+        api<Conversation>(`/api/conversations/${convId}`, {
+          method: 'PATCH',
+          body: { title: autoTitle },
+        })
+          .then(() => sidebarRef.current?.refresh())
+          .catch(() => {});
       }
 
+      // Optimistic user message in local UI state
       setMessages((prev) => [
         ...prev,
         {
           id: `user-${Date.now()}`,
-          conversationId,
-          role: 'user',
+          conversationId: convId,
+          role: 'user' as const,
           content,
           createdAt: new Date().toISOString(),
         },
       ]);
 
-      api<Message>(`/api/conversations/${conversationId}/messages`, {
+      // Persist the user message to the DB so conversation history is
+      // available when the page is reloaded or a new session starts.
+      api<Message>(`/api/conversations/${convId}/messages`, {
         method: 'POST',
         body: { role: 'user', content },
-      }).catch(() => {});
+      }).catch(() => {
+        // Non-fatal: the agent can still process the message even if
+        // REST persistence fails.
+      });
 
+      // Send to WebSocket — gateway creates/resumes the agent session and
+      // streams the response back via agent:start / agent:text / agent:end.
       const socket = getSocket();
       if (!socket.connected) {
         socket.connect();
       }
       socket.emit('message', {
-        conversationId,
+        conversationId: convId,
         content,
-        model: options?.modelId ?? selectedModelRef.current?.id,
+        modelId: (options?.modelId ?? selectedModelId) || undefined,
       });
     },
-    [activeId, conversations, messages.length],
+    [activeId, messages, selectedModelId],
   );
 
-  const handleStop = useCallback(() => {
-    const socket = getSocket();
-    socket.emit('cancel', { conversationId: activeIdRef.current });
-
-    const partialText = streamingTextRef.current.trim();
-    const partialThinking = streamingThinkingRef.current.trim();
-
-    if (partialText) {
-      setMessages((prev) => [
-        ...prev,
-        {
-          id: `assistant-partial-${Date.now()}`,
-          conversationId: activeIdRef.current ?? '',
-          role: 'assistant',
-          content: partialText,
-          thinking: partialThinking || undefined,
-          model: selectedModelRef.current?.name,
-          provider: selectedModelRef.current?.provider,
-          createdAt: new Date().toISOString(),
-        },
-      ]);
-    }
-
-    setIsStreaming(false);
-    setStreamingText('');
-    setStreamingThinking('');
-    streamingTextRef.current = '';
-    streamingThinkingRef.current = '';
-    destroySocket();
-  }, []);
-
-  const handleEditLastMessage = useCallback((): string | null => {
-    const lastUserMessage = [...messages].reverse().find((message) => message.role === 'user');
-    return lastUserMessage?.content ?? null;
-  }, [messages]);
-
-  const activeConversation =
-    conversations.find((conversation) => conversation.id === activeId) ?? null;
-
   return (
-    <div className="-m-6 flex h-[100dvh] overflow-hidden">
-      <ConversationList
-        conversations={conversations}
-        activeId={activeId}
-        isOpen={sidebarOpen}
-        onClose={() => setSidebarOpen(false)}
-        onSelect={setActiveId}
-        onNew={handleNewConversation}
-        onRename={handleRename}
-        onDelete={handleDelete}
-        onArchive={handleArchive}
+    <div
+      className="-m-6 flex h-[calc(100vh-3.5rem)] overflow-hidden"
+      style={{ background: 'var(--bg-deep, var(--color-surface-bg, #0a0f1a))' }}
+    >
+      <ConversationSidebar
+        ref={sidebarRef}
+        isOpen={isSidebarOpen}
+        onClose={() => setIsSidebarOpen(false)}
+        currentConversationId={activeId}
+        onSelectConversation={(conversationId) => {
+          setActiveId(conversationId);
+          setMessages([]);
+          if (conversationId && window.innerWidth < 768) {
+            setIsSidebarOpen(false);
+          }
+        }}
+        onNewConversation={(projectId) => {
+          void handleNewConversation(projectId);
+        }}
       />
 
-      <div
-        className="relative flex min-w-0 flex-1 flex-col overflow-hidden"
-        style={{
-          background:
-            'radial-gradient(circle at top, color-mix(in srgb, var(--color-ms-blue-500) 14%, transparent), transparent 35%), var(--color-bg)',
-        }}
-      >
-        <AppHeader
-          conversationTitle={activeConversation?.title}
-          isSidebarOpen={sidebarOpen}
-          onToggleSidebar={() => setSidebarOpen((prev) => !prev)}
-        />
-
-        <div className="flex-1 overflow-y-auto px-4 py-6 md:px-6">
-          <div className="mx-auto flex w-full max-w-4xl flex-col gap-4">
-            {messages.length === 0 && !isStreaming ? (
-              <div className="flex min-h-full flex-1 items-center justify-center py-16">
-                <div className="max-w-xl text-center">
-                  <div className="mb-4 text-xs uppercase tracking-[0.3em] text-[var(--color-muted)]">
-                    Mosaic Chat
-                  </div>
-                  <h2 className="text-3xl font-semibold text-[var(--color-text)]">
-                    Start a new session with a better chat interface.
-                  </h2>
-                  <p className="mt-3 text-sm leading-7 text-[var(--color-text-2)]">
-                    Pick a model, send a prompt, and the response area will keep reasoning,
-                    metadata, and streaming status visible without leaving the page.
-                  </p>
-                </div>
-              </div>
-            ) : null}
-
-            {messages.map((message) => (
-              <MessageBubble key={message.id} message={message} />
-            ))}
-
-            {isStreaming ? (
-              <StreamingMessage
-                text={streamingText}
-                thinking={streamingThinking}
-                modelName={selectedModel?.name ?? null}
-              />
-            ) : null}
-
-            <div ref={messagesEndRef} />
+      <div className="flex min-w-0 flex-1 flex-col">
+        <div
+          className="flex items-center gap-3 border-b px-4 py-3"
+          style={{ borderColor: 'var(--border)' }}
+        >
+          <button
+            type="button"
+            onClick={() => setIsSidebarOpen((open) => !open)}
+            className="rounded-lg border p-2 transition-colors"
+            style={{
+              borderColor: 'var(--border)',
+              background: 'var(--surface)',
+              color: 'var(--text)',
+            }}
+            aria-label={isSidebarOpen ? 'Close conversation sidebar' : 'Open conversation sidebar'}
+          >
+            <svg viewBox="0 0 24 24" className="h-4 w-4" fill="none" stroke="currentColor">
+              <path strokeWidth="2" strokeLinecap="round" d="M4 7h16M4 12h16M4 17h16" />
+            </svg>
+          </button>
+          <div>
+            <h1 className="text-sm font-semibold" style={{ color: 'var(--text)' }}>
+              Mosaic Chat
+            </h1>
+            <p className="text-xs" style={{ color: 'var(--muted)' }}>
+              {activeId ? 'Active conversation selected' : 'Choose or start a conversation'}
+            </p>
           </div>
         </div>
 
-        <div className="sticky bottom-0">
-          <div className="mx-auto w-full max-w-4xl">
+        {activeId ? (
+          <>
+            <div className="flex-1 space-y-4 overflow-y-auto p-6">
+              {messages.map((msg) => (
+                <MessageBubble key={msg.id} message={msg} />
+              ))}
+              {isStreaming && <StreamingMessage text={streamingText} />}
+              <div ref={messagesEndRef} />
+            </div>
             <ChatInput
               onSend={handleSend}
-              onStop={handleStop}
               isStreaming={isStreaming}
               models={models}
               selectedModelId={selectedModelId}
               onModelChange={setSelectedModelId}
-              onRequestEditLastMessage={handleEditLastMessage}
             />
+          </>
+        ) : (
+          <div className="flex flex-1 items-center justify-center px-6">
+            <div
+              className="max-w-md rounded-2xl border px-8 py-10 text-center"
+              style={{
+                borderColor: 'var(--border)',
+                background: 'var(--surface)',
+              }}
+            >
+              <h2 className="text-lg font-medium" style={{ color: 'var(--text)' }}>
+                Welcome to Mosaic Chat
+              </h2>
+              <p className="mt-1 text-sm" style={{ color: 'var(--muted)' }}>
+                Select a conversation or start a new one
+              </p>
+              <button
+                type="button"
+                onClick={() => {
+                  void handleNewConversation();
+                }}
+                className="mt-4 rounded-lg px-4 py-2 text-sm font-medium text-white transition-colors"
+                style={{ background: 'var(--primary)' }}
+              >
+                Start new conversation
+              </button>
+            </div>
           </div>
-        </div>
+        )}
       </div>
     </div>
   );
 }
-
-function normalizeMessage(message: Message): Message {
-  const metadata = message.metadata ?? {};
-
-  return {
-    ...message,
-    thinking:
-      message.thinking ?? (typeof metadata.thinking === 'string' ? metadata.thinking : undefined),
-    model: message.model ?? (typeof metadata.model === 'string' ? metadata.model : undefined),
-    provider:
-      message.provider ?? (typeof metadata.provider === 'string' ? metadata.provider : undefined),
-    promptTokens:
-      message.promptTokens ??
-      (typeof metadata.prompt_tokens === 'number' ? metadata.prompt_tokens : undefined),
-    completionTokens:
-      message.completionTokens ??
-      (typeof metadata.completion_tokens === 'number' ? metadata.completion_tokens : undefined),
-    totalTokens:
-      message.totalTokens ??
-      (typeof metadata.total_tokens === 'number' ? metadata.total_tokens : undefined),
-  };
-}
diff --git a/apps/web/src/components/chat/conversation-sidebar.tsx b/apps/web/src/components/chat/conversation-sidebar.tsx
new file mode 100644
index 0000000..8572461
--- /dev/null
+++ b/apps/web/src/components/chat/conversation-sidebar.tsx
@@ -0,0 +1,576 @@
+'use client';
+
+import {
+  forwardRef,
+  useCallback,
+  useEffect,
+  useImperativeHandle,
+  useMemo,
+  useRef,
+  useState,
+} from 'react';
+import { api } from '@/lib/api';
+import type { Conversation, Project } from '@/lib/types';
+
+export interface ConversationSummary {
+  id: string;
+  title: string | null;
+  projectId: string | null;
+  updatedAt: string;
+  archived?: boolean;
+}
+
+export interface ConversationSidebarRef {
+  refresh: () => void;
+  addConversation: (conversation: ConversationSummary) => void;
+}
+
+interface ConversationSidebarProps {
+  isOpen: boolean;
+  onClose: () => void;
+  currentConversationId: string | null;
+  onSelectConversation: (conversationId: string | null) => void;
+  onNewConversation: (projectId?: string | null) => void;
+}
+
+interface GroupedConversations {
+  key: string;
+  label: string;
+  projectId: string | null;
+  conversations: ConversationSummary[];
+}
+
+function toSummary(conversation: Conversation): ConversationSummary {
+  return {
+    id: conversation.id,
+    title: conversation.title,
+    projectId: conversation.projectId,
+    updatedAt: conversation.updatedAt,
+    archived: conversation.archived,
+  };
+}
+
+function formatRelativeTime(dateStr: string): string {
+  const date = new Date(dateStr);
+  const now = new Date();
+  const diffMs = now.getTime() - date.getTime();
+  const diffMinutes = Math.floor(diffMs / 60_000);
+  const diffHours = Math.floor(diffMs / 3_600_000);
+  const diffDays = Math.floor(diffMs / 86_400_000);
+
+  if (diffMinutes < 1) return 'Just now';
+  if (diffMinutes < 60) return `${diffMinutes}m ago`;
+  if (diffHours < 24) return `${diffHours}h ago`;
+  if (diffDays === 1) return 'Yesterday';
+  if (diffDays < 7) return `${diffDays}d ago`;
+
+  return date.toLocaleDateString(undefined, { month: 'short', day: 'numeric' });
+}
+
+export const ConversationSidebar = forwardRef<ConversationSidebarRef, ConversationSidebarProps>(
+  function ConversationSidebar(
+    { isOpen, onClose, currentConversationId, onSelectConversation, onNewConversation },
+    ref,
+  ): React.ReactElement {
+    const [conversations, setConversations] = useState<ConversationSummary[]>([]);
+    const [projects, setProjects] = useState<Project[]>([]);
+    const [searchQuery, setSearchQuery] = useState('');
+    const [isLoading, setIsLoading] = useState(true);
+    const [error, setError] = useState<string | null>(null);
+    const [renamingId, setRenamingId] = useState<string | null>(null);
+    const [renameValue, setRenameValue] = useState('');
+    const [pendingDeleteId, setPendingDeleteId] = useState<string | null>(null);
+    const [hoveredId, setHoveredId] = useState<string | null>(null);
+    const renameInputRef = useRef<HTMLInputElement>(null);
+
+    const loadSidebarData = useCallback(async (): Promise<void> => {
+      try {
+        setIsLoading(true);
+        setError(null);
+
+        const [loadedConversations, loadedProjects] = await Promise.all([
+          api<Conversation[]>('/api/conversations'),
+          api<Project[]>('/api/projects').catch(() => [] as Project[]),
+        ]);
+
+        setConversations(
+          loadedConversations
+            .filter((conversation) => !conversation.archived)
+            .map(toSummary)
+            .sort((a, b) => Date.parse(b.updatedAt) - Date.parse(a.updatedAt)),
+        );
+        setProjects(loadedProjects);
+      } catch (err) {
+        setError(err instanceof Error ? err.message : 'Failed to load conversations');
+      } finally {
+        setIsLoading(false);
+      }
+    }, []);
+
+    useEffect(() => {
+      void loadSidebarData();
+    }, [loadSidebarData]);
+
+    useEffect(() => {
+      if (!renamingId) return;
+      const timer = window.setTimeout(() => renameInputRef.current?.focus(), 0);
+      return () => window.clearTimeout(timer);
+    }, [renamingId]);
+
+    useImperativeHandle(
+      ref,
+      () => ({
+        refresh: () => {
+          void loadSidebarData();
+        },
+        addConversation: (conversation) => {
+          setConversations((prev) => {
+            const next = [conversation, ...prev.filter((item) => item.id !== conversation.id)];
+            return next.sort((a, b) => Date.parse(b.updatedAt) - Date.parse(a.updatedAt));
+          });
+        },
+      }),
+      [loadSidebarData],
+    );
+
+    const filteredConversations = useMemo(() => {
+      const query = searchQuery.trim().toLowerCase();
+      if (!query) return conversations;
+
+      return conversations.filter((conversation) =>
+        (conversation.title ?? 'Untitled conversation').toLowerCase().includes(query),
+      );
+    }, [conversations, searchQuery]);
+
+    const groupedConversations = useMemo<GroupedConversations[]>(() => {
+      if (projects.length === 0) {
+        return [
+          {
+            key: 'all',
+            label: 'All conversations',
+            projectId: null,
+            conversations: filteredConversations,
+          },
+        ];
+      }
+
+      const byProject = new Map<string | null, ConversationSummary[]>();
+      for (const conversation of filteredConversations) {
+        const key = conversation.projectId ?? null;
+        const items = byProject.get(key) ?? [];
+        items.push(conversation);
+        byProject.set(key, items);
+      }
+
+      const groups: GroupedConversations[] = [];
+
+      for (const project of projects) {
+        const projectConversations = byProject.get(project.id);
+        if (!projectConversations?.length) continue;
+
+        groups.push({
+          key: project.id,
+          label: project.name,
+          projectId: project.id,
+          conversations: projectConversations,
+        });
+      }
+
+      const ungrouped = byProject.get(null);
+      if (ungrouped?.length) {
+        groups.push({
+          key: 'general',
+          label: 'General',
+          projectId: null,
+          conversations: ungrouped,
+        });
+      }
+
+      if (groups.length === 0) {
+        groups.push({
+          key: 'all',
+          label: 'All conversations',
+          projectId: null,
+          conversations: filteredConversations,
+        });
+      }
+
+      return groups;
+    }, [filteredConversations, projects]);
+
+    const startRename = useCallback((conversation: ConversationSummary): void => {
+      setPendingDeleteId(null);
+      setRenamingId(conversation.id);
+      setRenameValue(conversation.title ?? '');
+    }, []);
+
+    const cancelRename = useCallback((): void => {
+      setRenamingId(null);
+      setRenameValue('');
+    }, []);
+
+    const commitRename = useCallback(async (): Promise<void> => {
+      if (!renamingId) return;
+
+      const title = renameValue.trim() || 'Untitled conversation';
+
+      try {
+        const updated = await api<Conversation>(`/api/conversations/${renamingId}`, {
+          method: 'PATCH',
+          body: { title },
+        });
+
+        const summary = toSummary(updated);
+        setConversations((prev) =>
+          prev
+            .map((conversation) => (conversation.id === renamingId ? summary : conversation))
+            .sort((a, b) => Date.parse(b.updatedAt) - Date.parse(a.updatedAt)),
+        );
+      } catch (err) {
+        setError(err instanceof Error ? err.message : 'Failed to rename conversation');
+      } finally {
+        setRenamingId(null);
+        setRenameValue('');
+      }
+    }, [renameValue, renamingId]);
+
+    const deleteConversation = useCallback(
+      async (conversationId: string): Promise<void> => {
+        try {
+          await api<void>(`/api/conversations/${conversationId}`, { method: 'DELETE' });
+          setConversations((prev) =>
+            prev.filter((conversation) => conversation.id !== conversationId),
+          );
+          if (currentConversationId === conversationId) {
+            onSelectConversation(null);
+          }
+        } catch (err) {
+          setError(err instanceof Error ? err.message : 'Failed to delete conversation');
+        } finally {
+          setPendingDeleteId(null);
+        }
+      },
+      [currentConversationId, onSelectConversation],
+    );
+
+    return (
+      <>
+        {isOpen ? (
+          <button
+            type="button"
+            aria-label="Close conversation sidebar"
+            className="fixed inset-0 z-30 bg-black/50 md:hidden"
+            onClick={onClose}
+          />
+        ) : null}
+
+        <aside
+          aria-label="Conversation sidebar"
+          className="fixed left-0 top-0 z-40 flex h-full flex-col border-r md:relative md:z-0"
+          style={{
+            width: 'var(--sidebar-w)',
+            background: 'var(--bg)',
+            borderColor: 'var(--border)',
+            transform: isOpen ? 'translateX(0)' : 'translateX(calc(-1 * var(--sidebar-w)))',
+            transition: 'transform 220ms var(--ease)',
+          }}
+        >
+          <div
+            className="flex items-center justify-between border-b px-4 py-3"
+            style={{ borderColor: 'var(--border)' }}
+          >
+            <div>
+              <p className="text-sm font-semibold" style={{ color: 'var(--text)' }}>
+                Conversations
+              </p>
+              <p className="text-xs" style={{ color: 'var(--muted)' }}>
+                Search, rename, and manage threads
+              </p>
+            </div>
+            <button
+              type="button"
+              onClick={onClose}
+              className="rounded-md p-2 md:hidden"
+              style={{ color: 'var(--text-2)' }}
+            >
+              <svg viewBox="0 0 24 24" className="h-4 w-4" fill="none" stroke="currentColor">
+                <path strokeWidth="2" strokeLinecap="round" d="M6 6l12 12M18 6 6 18" />
+              </svg>
+            </button>
+          </div>
+
+          <div className="space-y-3 border-b p-3" style={{ borderColor: 'var(--border)' }}>
+            <button
+              type="button"
+              onClick={() => onNewConversation(null)}
+              className="flex w-full items-center justify-center gap-2 rounded-lg border px-3 py-2 text-sm font-medium transition-colors"
+              style={{
+                borderColor: 'var(--primary)',
+                background: 'color-mix(in srgb, var(--primary) 12%, transparent)',
+                color: 'var(--text)',
+              }}
+            >
+              <svg viewBox="0 0 24 24" className="h-4 w-4" fill="none" stroke="currentColor">
+                <path strokeWidth="2" strokeLinecap="round" d="M12 5v14M5 12h14" />
+              </svg>
+              New conversation
+            </button>
+
+            <div className="relative">
+              <svg
+                viewBox="0 0 24 24"
+                className="pointer-events-none absolute left-3 top-1/2 h-4 w-4 -translate-y-1/2"
+                fill="none"
+                stroke="currentColor"
+                style={{ color: 'var(--muted)' }}
+              >
+                <circle cx="11" cy="11" r="7" strokeWidth="2" />
+                <path d="m20 20-3.5-3.5" strokeWidth="2" strokeLinecap="round" />
+              </svg>
+              <input
+                type="search"
+                value={searchQuery}
+                onChange={(event) => setSearchQuery(event.target.value)}
+                placeholder="Search conversations"
+                className="w-full rounded-lg border px-9 py-2 text-sm outline-none"
+                style={{
+                  background: 'var(--surface)',
+                  borderColor: 'var(--border)',
+                  color: 'var(--text)',
+                }}
+              />
+            </div>
+          </div>
+
+          <div className="flex-1 overflow-y-auto p-3">
+            {isLoading ? (
+              <div className="py-8 text-center text-sm" style={{ color: 'var(--muted)' }}>
+                Loading conversations...
+              </div>
+            ) : error ? (
+              <div
+                className="space-y-3 rounded-xl border p-4 text-sm"
+                style={{
+                  background: 'color-mix(in srgb, var(--danger) 10%, var(--surface))',
+                  borderColor: 'color-mix(in srgb, var(--danger) 35%, var(--border))',
+                  color: 'var(--text)',
+                }}
+              >
+                <p>{error}</p>
+                <button
+                  type="button"
+                  onClick={() => void loadSidebarData()}
+                  className="rounded-md px-3 py-1.5 text-xs font-medium"
+                  style={{ background: 'var(--danger)', color: 'white' }}
+                >
+                  Retry
+                </button>
+              </div>
+            ) : filteredConversations.length === 0 ? (
+              <div className="py-10 text-center">
+                <p className="text-sm" style={{ color: 'var(--text-2)' }}>
+                  {searchQuery ? 'No matching conversations' : 'No conversations yet'}
+                </p>
+                <p className="mt-1 text-xs" style={{ color: 'var(--muted)' }}>
+                  {searchQuery ? 'Try another title search.' : 'Start a new conversation to begin.'}
+                </p>
+              </div>
+            ) : (
+              <div className="space-y-4">
+                {groupedConversations.map((group) => (
+                  <section key={group.key} className="space-y-2">
+                    {projects.length > 0 ? (
+                      <div className="flex items-center justify-between px-1">
+                        <h3
+                          className="text-[11px] font-semibold uppercase tracking-[0.16em]"
+                          style={{ color: 'var(--muted)' }}
+                        >
+                          {group.label}
+                        </h3>
+                        <button
+                          type="button"
+                          onClick={() => onNewConversation(group.projectId)}
+                          className="rounded-md px-2 py-1 text-[11px] font-medium"
+                          style={{ color: 'var(--ms-blue-500)' }}
+                        >
+                          New
+                        </button>
+                      </div>
+                    ) : null}
+
+                    <div className="space-y-1">
+                      {group.conversations.map((conversation) => {
+                        const isActive = currentConversationId === conversation.id;
+                        const isRenaming = renamingId === conversation.id;
+                        const showActions =
+                          hoveredId === conversation.id ||
+                          isRenaming ||
+                          pendingDeleteId === conversation.id;
+
+                        return (
+                          <div
+                            key={conversation.id}
+                            onMouseEnter={() => setHoveredId(conversation.id)}
+                            onMouseLeave={() =>
+                              setHoveredId((current) =>
+                                current === conversation.id ? null : current,
+                              )
+                            }
+                            className="rounded-xl border p-2 transition-colors"
+                            style={{
+                              borderColor: isActive
+                                ? 'color-mix(in srgb, var(--primary) 60%, var(--border))'
+                                : 'transparent',
+                              background: isActive ? 'var(--surface-2)' : 'transparent',
+                            }}
+                          >
+                            {isRenaming ? (
+                              <input
+                                ref={renameInputRef}
+                                value={renameValue}
+                                onChange={(event) => setRenameValue(event.target.value)}
+                                onBlur={() => void commitRename()}
+                                onKeyDown={(event) => {
+                                  if (event.key === 'Enter') {
+                                    event.preventDefault();
+                                    void commitRename();
+                                  }
+                                  if (event.key === 'Escape') {
+                                    event.preventDefault();
+                                    cancelRename();
+                                  }
+                                }}
+                                maxLength={255}
+                                className="w-full rounded-md border px-2 py-1.5 text-sm outline-none"
+                                style={{
+                                  background: 'var(--surface)',
+                                  borderColor: 'var(--ms-blue-500)',
+                                  color: 'var(--text)',
+                                }}
+                              />
+                            ) : (
+                              <button
+                                type="button"
+                                onClick={() => onSelectConversation(conversation.id)}
+                                className="block w-full text-left"
+                              >
+                                <div className="flex items-start gap-2">
+                                  <div className="min-w-0 flex-1">
+                                    <p
+                                      className="truncate text-sm font-medium"
+                                      style={{
+                                        color: isActive ? 'var(--text)' : 'var(--text-2)',
+                                      }}
+                                    >
+                                      {conversation.title ?? 'Untitled conversation'}
+                                    </p>
+                                    <p className="mt-1 text-xs" style={{ color: 'var(--muted)' }}>
+                                      {formatRelativeTime(conversation.updatedAt)}
+                                    </p>
+                                  </div>
+
+                                  {showActions ? (
+                                    <div className="flex items-center gap-1">
+                                      <button
+                                        type="button"
+                                        onClick={(event) => {
+                                          event.stopPropagation();
+                                          startRename(conversation);
+                                        }}
+                                        className="rounded-md p-1.5 transition-colors"
+                                        style={{ color: 'var(--text-2)' }}
+                                        aria-label={`Rename ${conversation.title ?? 'conversation'}`}
+                                      >
+                                        <svg
+                                          viewBox="0 0 24 24"
+                                          className="h-3.5 w-3.5"
+                                          fill="none"
+                                          stroke="currentColor"
+                                        >
+                                          <path
+                                            d="M4 20h4l10.5-10.5a1.4 1.4 0 0 0 0-2L16.5 5.5a1.4 1.4 0 0 0-2 0L4 16v4Z"
+                                            strokeWidth="1.8"
+                                            strokeLinejoin="round"
+                                          />
+                                        </svg>
+                                      </button>
+                                      <button
+                                        type="button"
+                                        onClick={(event) => {
+                                          event.stopPropagation();
+                                          setPendingDeleteId((current) =>
+                                            current === conversation.id ? null : conversation.id,
+                                          );
+                                          setRenamingId(null);
+                                        }}
+                                        className="rounded-md p-1.5 transition-colors"
+                                        style={{ color: 'var(--danger)' }}
+                                        aria-label={`Delete ${conversation.title ?? 'conversation'}`}
+                                      >
+                                        <svg
+                                          viewBox="0 0 24 24"
+                                          className="h-3.5 w-3.5"
+                                          fill="none"
+                                          stroke="currentColor"
+                                        >
+                                          <path
+                                            d="M4 7h16M10 11v6M14 11v6M6 7l1 12h10l1-12M9 7V4h6v3"
+                                            strokeWidth="1.8"
+                                            strokeLinecap="round"
+                                            strokeLinejoin="round"
+                                          />
+                                        </svg>
+                                      </button>
+                                    </div>
+                                  ) : null}
+                                </div>
+                              </button>
+                            )}
+
+                            {pendingDeleteId === conversation.id ? (
+                              <div
+                                className="mt-2 flex items-center justify-between rounded-lg border px-2 py-2"
+                                style={{
+                                  borderColor:
+                                    'color-mix(in srgb, var(--danger) 45%, var(--border))',
+                                  background:
+                                    'color-mix(in srgb, var(--danger) 10%, var(--surface))',
+                                }}
+                              >
+                                <p className="text-xs" style={{ color: 'var(--text-2)' }}>
+                                  Delete this conversation?
+                                </p>
+                                <div className="flex items-center gap-2">
+                                  <button
+                                    type="button"
+                                    onClick={() => setPendingDeleteId(null)}
+                                    className="rounded-md px-2 py-1 text-xs"
+                                    style={{ color: 'var(--text-2)' }}
+                                  >
+                                    Cancel
+                                  </button>
+                                  <button
+                                    type="button"
+                                    onClick={() => void deleteConversation(conversation.id)}
+                                    className="rounded-md px-2 py-1 text-xs font-medium"
+                                    style={{ background: 'var(--danger)', color: 'white' }}
+                                  >
+                                    Delete
+                                  </button>
+                                </div>
+                              </div>
+                            ) : null}
+                          </div>
+                        );
+                      })}
+                    </div>
+                  </section>
+                ))}
+              </div>
+            )}
+          </div>
+        </aside>
+      </>
+    );
+  },
+);