feat(chat): autoscroll to newest message

apps/web/src/components/emoji-chat.tsx

@@ -4,6 +4,46 @@ import { useCallback, useEffect, useRef, useState } from "react";
 import { createPortal } from "react-dom";
 import data from "@emoji-mart/data";
 import Picker from "@emoji-mart/react";
+import type { ChatMessage } from "@together/shared";
+
+/**
+ * Scrollable chat log that keeps the newest message in view. Auto-scrolls only
+ * when the viewer is already pinned to the bottom, so scrolling up to re-read
+ * history is not interrupted by incoming messages.
+ */
+export function ChatMessages({ messages }: { messages: ChatMessage[] }) {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const pinnedToBottomRef = useRef(true);
+
+  const handleScroll = useCallback(() => {
+    const el = containerRef.current;
+    if (!el) return;
+    const distanceFromBottom = el.scrollHeight - el.scrollTop - el.clientHeight;
+    pinnedToBottomRef.current = distanceFromBottom < 48;
+  }, []);
+
+  useEffect(() => {
+    const el = containerRef.current;
+    if (!el || !pinnedToBottomRef.current) return;
+    el.scrollTop = el.scrollHeight;
+  }, [messages.length]);
+
+  return (
+    <div
+      ref={containerRef}
+      onScroll={handleScroll}
+      className="min-h-0 flex-1 overflow-y-auto p-3 space-y-2"
+    >
+      {messages.map((msg) => (
+        <div key={msg.id} className="text-sm">
+          <span className="font-medium text-[var(--accent)]">{msg.senderName}</span>
+          <span className="mx-1 text-[var(--text-muted)]">·</span>
+          <span>{msg.body}</span>
+        </div>
+      ))}
+    </div>
+  );
+}
 
 interface EmojiPickerButtonProps {
   onSelect: (emoji: string) => void;

apps/web/src/components/room-client.tsx

@@ -33,7 +33,7 @@ import {
 } from "lucide-react";
 import { useRoomSocket } from "@/hooks/use-room-socket";
 import { useYouTubePlayer } from "@/hooks/use-youtube-player";
-import { ChatInput } from "@/components/emoji-chat";
+import { ChatInput, ChatMessages } from "@/components/emoji-chat";
 import { PlaybackSeekBar } from "@/components/playback-seek-bar";
 import { SettingsDrawer } from "@/components/room-settings";
 import { useUserPreferences } from "@/hooks/use-user-preferences";
@@ -410,15 +410,7 @@ export function RoomClient({
 
   const chatPanel = (
     <>
-      <div className="min-h-0 flex-1 overflow-y-auto p-3 space-y-2">
-        {roomState?.chat.map((msg) => (
-          <div key={msg.id} className="text-sm">
-            <span className="font-medium text-[var(--accent)]">{msg.senderName}</span>
-            <span className="mx-1 text-[var(--text-muted)]">·</span>
-            <span>{msg.body}</span>
-          </div>
-        ))}
-      </div>
+      <ChatMessages messages={roomState?.chat ?? []} />
       <ChatInput
         onSend={(body) => send({ type: "chat", body })}
         slowModeSeconds={settings?.slowModeSeconds}