fix: only join the initial channel after registration is complete

During registration, only a subset of commands are allowed.
Servers MUST send a RPL_WELCOME (001) after registration is complete so
we join the channel in response to that numeric reply.

https://modern.ircdocs.horse/#connection-registration

irc/client.go

@@ -84,6 +84,9 @@ type Client struct {
 	// Active channel index
 	ActiveChannelIndex int
 
+	// The channel to join immediately after registration completes.
+	InitialChannel string
+
 	// Reference to the bubbletea program
 	Tea *tea.Program
 
@@ -213,10 +216,6 @@ func (c *Client) Register(nick string, password string, channel string) {
 	// set user-wanted nickname
 	c.Nickname = nick
 	c.SendCommand(commands.USER, nick, "0", "*", nick)
-	// joining a channel when registering is optional
-	if channel != "" {
-		c.SendCommand(commands.JOIN, channel)
-	}
 }
 
 func (c *Client) SetDay() {

irc/handler/handler.go

@@ -371,9 +371,15 @@ func handleWELCOME(msg irc.Message, client *irc.Client) {
 		AsServerMsg:   true,
 	}
 
-	// set server-registered nickname
+	// set server-registered nickname because the server MAY return a different nickname than
+	// the one the user chose because of length restrictions or otherwise.
 	client.Nickname = nick
 	client.Channels[0].AppendMsg(msg.Timestamp, welcomeMsg, msgOpts)
+
+	// Only join the user-requested channel AFTER registration is complete.
+	if client.InitialChannel != "" {
+		client.SendCommand(commands.JOIN, client.InitialChannel)
+	}
 }
 
 func handleYOURHOST(msg irc.Message, client *irc.Client) {

ui/app/app.go

@@ -91,6 +91,7 @@ func (s State) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		tlsEnabled := s.UI.Login.TLS
 
 		s.UI.CurrentScreen = MainScreen
+		s.Client.InitialChannel = channel
 
 		s.Client.Initialize(host, port, tlsEnabled)
 		s.Client.Register(nickname, password, channel)