feat: add in-game chat to Connect 4

Add real-time chat alongside the game board, mirroring the snake chat
implementation. Fix mobile layout for both C4 and snake chats — expand
chat to full width and reduce history height on small screens.

assets/css/input.css

@@ -111,6 +111,8 @@
 }
 @media (max-width: 768px) {
   .snake-game-area { flex-direction: column; align-items: center; }
+  .snake-game-area .snake-chat { width: 100%; max-width: 480px; }
+  .snake-chat-history { height: 150px; }
 }
 
 /* Snake chat */
@@ -152,3 +154,56 @@
   font-size: 0.85rem;
 }
 .snake-chat-input button:hover { background: #667; }
+
+/* C4 game area: board + chat side-by-side */
+.c4-game-area {
+  display: flex;
+  gap: 16px;
+  align-items: flex-start;
+  justify-content: center;
+}
+@media (max-width: 768px) {
+  .c4-game-area { flex-direction: column; align-items: center; }
+  .c4-game-area .c4-chat { width: 100%; max-width: 480px; }
+  .c4-chat-history { height: 150px; }
+}
+
+/* C4 chat */
+.c4-chat { width: 100%; max-width: 480px; }
+.c4-game-area .c4-chat { width: 260px; max-width: none; flex-shrink: 0; }
+.c4-chat-history {
+  height: 300px;
+  overflow-y: auto;
+  background: #334;
+  border-radius: 8px 8px 0 0;
+  padding: 8px;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+.c4-chat-msg { font-size: 0.85rem; line-height: 1.3; }
+.c4-chat-input {
+  display: flex;
+  gap: 0;
+  background: #445;
+  border-radius: 0 0 8px 8px;
+  overflow: hidden;
+}
+.c4-chat-input input {
+  flex: 1;
+  padding: 6px 10px;
+  background: transparent;
+  border: none;
+  color: inherit;
+  outline: none;
+  font-size: 0.85rem;
+}
+.c4-chat-input button {
+  padding: 6px 14px;
+  background: #556;
+  border: none;
+  color: inherit;
+  cursor: pointer;
+  font-size: 0.85rem;
+}
+.c4-chat-input button:hover { background: #667; }

assets/css/output.css

@@ -1647,6 +1647,13 @@
     flex-direction: column;
     align-items: center;
   }
+  .snake-game-area .snake-chat {
+    width: 100%;
+    max-width: 480px;
+  }
+  .snake-chat-history {
+    height: 150px;
+  }
 }
 .snake-chat {
   width: 100%;
@@ -1698,6 +1705,75 @@
 .snake-chat-input button:hover {
   background: #667;
 }
+.c4-game-area {
+  display: flex;
+  gap: 16px;
+  align-items: flex-start;
+  justify-content: center;
+}
+@media (max-width: 768px) {
+  .c4-game-area {
+    flex-direction: column;
+    align-items: center;
+  }
+  .c4-game-area .c4-chat {
+    width: 100%;
+    max-width: 480px;
+  }
+  .c4-chat-history {
+    height: 150px;
+  }
+}
+.c4-chat {
+  width: 100%;
+  max-width: 480px;
+}
+.c4-game-area .c4-chat {
+  width: 260px;
+  max-width: none;
+  flex-shrink: 0;
+}
+.c4-chat-history {
+  height: 300px;
+  overflow-y: auto;
+  background: #334;
+  border-radius: 8px 8px 0 0;
+  padding: 8px;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+.c4-chat-msg {
+  font-size: 0.85rem;
+  line-height: 1.3;
+}
+.c4-chat-input {
+  display: flex;
+  gap: 0;
+  background: #445;
+  border-radius: 0 0 8px 8px;
+  overflow: hidden;
+}
+.c4-chat-input input {
+  flex: 1;
+  padding: 6px 10px;
+  background: transparent;
+  border: none;
+  color: inherit;
+  outline: none;
+  font-size: 0.85rem;
+}
+.c4-chat-input button {
+  padding: 6px 14px;
+  background: #556;
+  border: none;
+  color: inherit;
+  cursor: pointer;
+  font-size: 0.85rem;
+}
+.c4-chat-input button:hover {
+  background: #667;
+}
 @layer base {
   :where(:root),:root:has(input.theme-controller[value=light]:checked),[data-theme=light] {
     color-scheme: light;

main.go

@@ -353,6 +353,9 @@ func main() {
 		nickname := c.Signal(sessionNickname)
 		colSignal := c.Signal(0)
 		showGuestPrompt := c.Signal(false)
+		chatMsg := c.Signal("")
+		var chatMessages []ui.C4ChatMessage
+		var chatMu sync.Mutex
 
 		goToLogin := c.Action(func() {
 			c.Session().Set("return_url", "/game/"+gameID)
@@ -434,8 +437,53 @@ func main() {
 			}
 		})
 
+		sendChat := c.Action(func() {
+			msg := chatMsg.String()
+			if msg == "" || gi == nil {
+				return
+			}
+			color := gi.GetPlayerColor(playerID)
+			if color == 0 {
+				return
+			}
+			g := gi.GetGame()
+			nick := ""
+			for _, p := range g.Players {
+				if p != nil && p.ID == playerID {
+					nick = p.Nickname
+					break
+				}
+			}
+			cm := ui.C4ChatMessage{
+				Nickname: nick,
+				Color:    color,
+				Message:  msg,
+				Time:     time.Now().UnixMilli(),
+			}
+			data, err := json.Marshal(cm)
+			if err != nil {
+				return
+			}
+			c.Publish("game.chat."+gameID, data)
+			chatMsg.SetValue("")
+		})
+
 		if gameExists {
 			c.Subscribe("game."+gameID, func(data []byte) { c.Sync() })
+
+			c.Subscribe("game.chat."+gameID, func(data []byte) {
+				var cm ui.C4ChatMessage
+				if err := json.Unmarshal(data, &cm); err != nil {
+					return
+				}
+				chatMu.Lock()
+				chatMessages = append(chatMessages, cm)
+				if len(chatMessages) > 50 {
+					chatMessages = chatMessages[len(chatMessages)-50:]
+				}
+				chatMu.Unlock()
+				c.Sync()
+			})
 		}
 
 		if gameExists && sessionNickname != "" && gi.GetPlayerColor(playerID) == 0 {
@@ -480,13 +528,19 @@ func main() {
 				return dropPiece.OnClick(via.WithSignalInt(colSignal, col))
 			}
 
+			chatMu.Lock()
+			msgs := make([]ui.C4ChatMessage, len(chatMessages))
+			copy(msgs, chatMessages)
+			chatMu.Unlock()
+			chat := ui.C4Chat(msgs, chatMsg.Bind(), sendChat.OnClick(), sendChat.OnKeyDown("Enter"))
+
 			var content []h.H
 			content = append(content,
 				ui.BackToLobby(),
 				ui.StealthTitle("text-3xl font-bold"),
 				ui.PlayerInfo(g, myColor),
 				ui.StatusBanner(g, myColor, createRematch.OnClick()),
-				ui.BoardComponent(g, columnClick, myColor),
+				h.Div(h.Class("c4-game-area"), ui.BoardComponent(g, columnClick, myColor), chat),
 			)
 
 			if g.Status == game.StatusWaitingForPlayer {

ui/c4chat.go

@@ -0,0 +1,64 @@
+package ui
+
+import (
+	"fmt"
+
+	"github.com/ryanhamamura/via/h"
+)
+
+type C4ChatMessage struct {
+	Nickname string `json:"nickname"`
+	Color    int    `json:"color"` // 1=Red, 2=Yellow
+	Message  string `json:"message"`
+	Time     int64  `json:"time"`
+}
+
+var c4ChatColors = map[int]string{
+	1: "#4a2a3a",
+	2: "#2a4545",
+}
+
+func C4Chat(messages []C4ChatMessage, msgBind, sendClick, sendKeyDown h.H) h.H {
+	var msgEls []h.H
+	for _, m := range messages {
+		color := "#666"
+		if c, ok := c4ChatColors[m.Color]; ok {
+			color = c
+		}
+		msgEls = append(msgEls, h.Div(h.Class("c4-chat-msg"),
+			h.Span(
+				h.Attr("style", fmt.Sprintf("color:%s;font-weight:bold;", color)),
+				h.Text(m.Nickname+": "),
+			),
+			h.Span(h.Text(m.Message)),
+		))
+	}
+
+	autoScroll := h.Script(h.Text(`
+(function(){
+  var el = document.querySelector('.c4-chat-history');
+  if (!el) return;
+  el.scrollTop = el.scrollHeight;
+  new MutationObserver(function(){ el.scrollTop = el.scrollHeight; })
+    .observe(el, {childList:true, subtree:true});
+})();
+`))
+
+	historyAttrs := []h.H{h.Class("c4-chat-history")}
+	historyAttrs = append(historyAttrs, msgEls...)
+	historyAttrs = append(historyAttrs, autoScroll)
+
+	return h.Div(h.Class("c4-chat"),
+		h.Div(historyAttrs...),
+		h.Div(h.Class("c4-chat-input"),
+			h.Input(
+				h.Type("text"),
+				h.Attr("placeholder", "Chat..."),
+				h.Attr("autocomplete", "off"),
+				msgBind,
+				sendKeyDown,
+			),
+			h.Button(h.Type("button"), h.Text("Send"), sendClick),
+		),
+	)
+}