Add dummy TAGMSG command handler

sable_ircd/src/command/handlers/tagmsg.rs

@@ -0,0 +1,10 @@
+use super::*;
+
+/// Minimal implementation of TAGMSG that just drops everything, so we can safely
+/// implement https://ircv3.net/specs/extensions/message-tags
+///
+/// `CLIENTTAGDENY=*` tells clients we would drop all tags, anyway.
+#[command_handler("TAGMSG")]
+fn handle_tagmsg() -> CommandResult {
+    Ok(())
+}

sable_ircd/src/command/mod.rs

@@ -62,6 +62,7 @@ mod handlers {
     mod quit;
     pub mod register;
     mod rename;
+    mod tagmsg;
     mod topic;
     mod user;
     mod userhost;