refactor(chat): polish chat UI with design system tokens and components

- Replace raw <button> with <Button variant="ghost" size="icon-sm"> in header and history
- Add aria-expanded:bg-accent to agent selector trigger for open state
- Add max-h-60, w-auto max-w-56, truncate to agent dropdown
- Switch FAB to bg-card, chat window to bg-sidebar
- Switch user message bubble from bg-primary to bg-muted, drop text-primary-foreground
- Reduce user bubble max-w from 85% to 80%
- Remove agent avatar from AI messages, make AI content w-full
- Strip arbitrary text-[10px] from AvatarFallback
- Remove manual icon size overrides inside Button components

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/views/chat/components/chat-fab.tsx

@@ -18,7 +18,7 @@ export function ChatFab() {
     <Tooltip>
       <TooltipTrigger
         onClick={toggle}
-        className="fixed bottom-4 right-4 z-50 flex size-10 cursor-pointer items-center justify-center rounded-full border bg-background text-muted-foreground shadow-sm transition-transform hover:scale-110 hover:text-accent-foreground active:scale-95"
+        className="fixed bottom-4 right-4 z-50 flex size-10 cursor-pointer items-center justify-center rounded-full ring-1 ring-foreground/10 bg-card text-muted-foreground shadow-sm transition-transform hover:scale-110 hover:text-accent-foreground active:scale-95"
       >
         <MessageCircle className="size-5" />
       </TooltipTrigger>

packages/views/chat/components/chat-input.tsx

@@ -25,7 +25,7 @@ export function ChatInput({ onSend, onStop, isRunning, disabled }: ChatInputProp
 
   return (
     <div className="p-2 pt-0">
-      <div className="relative flex min-h-16 max-h-40 flex-col rounded-lg bg-card pb-8 ring-1 ring-border">
+      <div className="relative flex min-h-16 max-h-40 flex-col rounded-lg bg-card pb-8 border-1 border-border transition-colors focus-within:border-brand">
         <div className="flex-1 min-h-0 overflow-y-auto px-3 py-2">
           <ContentEditor
             ref={editorRef}

packages/views/chat/components/chat-message-list.tsx

@@ -45,20 +45,12 @@ export function ChatMessageList({
       ))}
       {/* Live streaming timeline */}
       {hasTimeline && (
-        <div className="flex items-start gap-3">
-          <AgentAvatar agent={agent} />
-          <div className="min-w-0 flex-1 space-y-1.5">
-            <TimelineView items={timelineItems} />
-          </div>
+        <div className="w-full space-y-1.5">
+          <TimelineView items={timelineItems} />
         </div>
       )}
       {isWaiting && !hasTimeline && (
-        <div className="flex items-start gap-3">
-          <AgentAvatar agent={agent} />
-          <div className="flex items-center pt-1">
-            <Loader2 className="size-4 animate-spin text-muted-foreground" />
-          </div>
-        </div>
+        <Loader2 className="size-4 animate-spin text-muted-foreground" />
       )}
       <div ref={bottomRef} />
     </div>
@@ -77,7 +69,7 @@ function MessageBubble({
   if (message.role === "user") {
     return (
       <div className="flex justify-end">
-        <div className="rounded-2xl bg-primary px-3.5 py-2 text-sm text-primary-foreground max-w-[85%] whitespace-pre-wrap break-words">
+        <div className="rounded-2xl bg-muted px-3.5 py-2 text-sm max-w-[80%] whitespace-pre-wrap break-words">
           {message.content}
         </div>
       </div>
@@ -116,17 +108,14 @@ function AssistantMessage({
   );
 
   return (
-    <div className="flex items-start gap-3">
-      <AgentAvatar agent={agent} />
-      <div className="min-w-0 flex-1 space-y-1.5">
-        {timeline.length > 0 ? (
-          <TimelineView items={timeline} />
-        ) : (
-          <div className="text-sm leading-relaxed prose prose-sm dark:prose-invert max-w-none">
-            <Markdown>{message.content}</Markdown>
-          </div>
-        )}
-      </div>
+    <div className="w-full space-y-1.5">
+      {timeline.length > 0 ? (
+        <TimelineView items={timeline} />
+      ) : (
+        <div className="text-sm leading-relaxed prose prose-sm dark:prose-invert max-w-none">
+          <Markdown>{message.content}</Markdown>
+        </div>
+      )}
     </div>
   );
 }

packages/views/chat/components/chat-session-history.tsx

@@ -2,6 +2,7 @@
 
 import { useQuery } from "@tanstack/react-query";
 import { ArrowLeft, MessageSquare, Archive, Trash2 } from "lucide-react";
+import { Button } from "@multica/ui/components/ui/button";
 import { Avatar, AvatarFallback, AvatarImage } from "@multica/ui/components/ui/avatar";
 import { Bot } from "lucide-react";
 import { useWorkspaceId } from "@multica/core/hooks";
@@ -47,12 +48,14 @@ export function ChatSessionHistory() {
     <div className="flex flex-1 flex-col overflow-hidden">
       {/* Header */}
       <div className="flex items-center gap-2 border-b px-4 py-2.5">
-        <button
+        <Button
+          variant="ghost"
+          size="icon-sm"
+          className="text-muted-foreground"
           onClick={() => setShowHistory(false)}
-          className="flex size-7 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground"
         >
-          <ArrowLeft className="size-3.5" />
-        </button>
+          <ArrowLeft />
+        </Button>
         <span className="text-sm font-medium">Chat History</span>
       </div>
 
@@ -151,7 +154,7 @@ function SessionItem({
     >
       <Avatar className="size-6 shrink-0 mt-0.5">
         {agent?.avatar_url && <AvatarImage src={agent.avatar_url} />}
-        <AvatarFallback className="bg-purple-100 text-purple-700 text-[10px]">
+        <AvatarFallback className="bg-purple-100 text-purple-700">
           <Bot className="size-3" />
         </AvatarFallback>
       </Avatar>
@@ -174,13 +177,15 @@ function SessionItem({
         </div>
       </div>
       {onArchive && (
-        <button
+        <Button
+          variant="ghost"
+          size="icon-sm"
+          className="invisible group-hover:visible text-muted-foreground hover:text-destructive shrink-0 mt-0.5"
           onClick={onArchive}
           title="Archive"
-          className="invisible group-hover:visible flex size-6 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-destructive shrink-0 mt-0.5"
         >
-          <Trash2 className="size-3" />
-        </button>
+          <Trash2 />
+        </Button>
       )}
     </button>
   );

packages/views/chat/components/chat-window.tsx

@@ -4,6 +4,7 @@ import { useCallback, useEffect, useRef } from "react";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { Minus, Maximize2, Minimize2, Send, ChevronDown, Bot, Plus, History } from "lucide-react";
 import { Avatar, AvatarFallback, AvatarImage } from "@multica/ui/components/ui/avatar";
+import { Button } from "@multica/ui/components/ui/button";
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -226,8 +227,8 @@ export function ChatWindow() {
   const hasMessages = messages.length > 0 || timelineItems.length > 0;
 
   const containerClass = isFullscreen
-    ? "fixed inset-y-0 right-0 z-50 flex flex-col w-[50%] border-l bg-background shadow-2xl"
-    : "fixed bottom-4 right-4 z-50 flex flex-col w-[420px] h-[600px] rounded-xl border bg-background shadow-2xl overflow-hidden";
+    ? "fixed top-4 right-4 bottom-4 z-50 flex flex-col w-[50%] rounded-xl ring-1 ring-foreground/10 bg-sidebar shadow-2xl overflow-hidden"
+    : "fixed bottom-4 right-4 z-50 flex flex-col w-[420px] h-[600px] rounded-xl ring-1 ring-foreground/10 bg-sidebar shadow-2xl overflow-hidden";
 
   return (
     <div className={containerClass}>
@@ -240,38 +241,46 @@ export function ChatWindow() {
             onSelect={handleSelectAgent}
           />
           <div className="flex items-center gap-0.5">
-            <button
+            <Button
+              variant="ghost"
+              size="icon-sm"
+              className="text-muted-foreground"
               onClick={() => setShowHistory(true)}
               title="Chat history"
-              className="flex size-7 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground"
             >
-              <History className="size-3.5" />
-            </button>
-            <button
+              <History />
+            </Button>
+            <Button
+              variant="ghost"
+              size="icon-sm"
+              className="text-muted-foreground"
               onClick={() => {
                 setActiveSession(null);
                 clearTimeline();
                 setPendingTask(null);
               }}
               title="New chat"
-              className="flex size-7 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground"
             >
-              <Plus className="size-3.5" />
-            </button>
-            <button
+              <Plus />
+            </Button>
+            <Button
+              variant="ghost"
+              size="icon-sm"
+              className="text-muted-foreground"
               onClick={toggleFullscreen}
               title={isFullscreen ? "Exit fullscreen" : "Fullscreen"}
-              className="flex size-7 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground"
             >
-              {isFullscreen ? <Minimize2 className="size-3.5" /> : <Maximize2 className="size-3.5" />}
-            </button>
-            <button
+              {isFullscreen ? <Minimize2 /> : <Maximize2 />}
+            </Button>
+            <Button
+              variant="ghost"
+              size="icon-sm"
+              className="text-muted-foreground"
               onClick={() => setOpen(false)}
               title="Minimize"
-              className="flex size-7 items-center justify-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground"
             >
-              <Minus className="size-3.5" />
-            </button>
+              <Minus />
+            </Button>
           </div>
         </div>
       )}
@@ -329,20 +338,20 @@ function AgentSelector({
 
   return (
     <DropdownMenu>
-      <DropdownMenuTrigger className="flex items-center gap-2 rounded-md px-1.5 py-1 -ml-1.5 transition-colors hover:bg-accent">
+      <DropdownMenuTrigger className="flex items-center gap-2 rounded-md px-1.5 py-1 -ml-1.5 transition-colors hover:bg-accent aria-expanded:bg-accent">
         <AgentAvatarSmall agent={activeAgent} />
         <span className="text-sm font-medium">{activeAgent.name}</span>
         <ChevronDown className="size-3 text-muted-foreground" />
       </DropdownMenuTrigger>
-      <DropdownMenuContent align="start">
+      <DropdownMenuContent align="start" className="max-h-60 w-auto max-w-56">
         {agents.map((agent) => (
           <DropdownMenuItem
             key={agent.id}
             onClick={() => onSelect(agent)}
-            className="flex items-center gap-2"
+            className="flex min-w-0 items-center gap-2"
           >
             <AgentAvatarSmall agent={agent} />
-            <span>{agent.name}</span>
+            <span className="truncate">{agent.name}</span>
           </DropdownMenuItem>
         ))}
       </DropdownMenuContent>
@@ -354,7 +363,7 @@ function AgentAvatarSmall({ agent }: { agent: Agent }) {
   return (
     <Avatar className="size-5">
       {agent.avatar_url && <AvatarImage src={agent.avatar_url} />}
-      <AvatarFallback className="bg-purple-100 text-purple-700 text-[10px]">
+      <AvatarFallback className="bg-purple-100 text-purple-700">
         <Bot className="size-3" />
       </AvatarFallback>
     </Avatar>