feat(userspace): Call/ReplyRecv IPC, malformed-request replies, servers exit on dead endpoint; drop send/receive compat, select!, async_syscall

crates/apps/snake/src/main.rs

@@ -18,9 +18,7 @@ const TICK_DELAY: u64 = 5_000_000;
 const MAX_RENDER_CMDS: usize = 140;
 
 fn display_send(req: &DisplayRequest) {
-    let words = req.encode();
-    syscall::send(DISPLAY_EP, words[0], words[1], words[2], words[3]);
-    syscall::receive(DISPLAY_EP);
+    let _ = syscall::request(DISPLAY_EP, req.encode());
 }
 
 fn draw_rect(x: u16, y: u16, w: u16, h: u16, color: u32) {
@@ -67,8 +65,9 @@ extern "C" fn main() {
 fn handle_input(snake: &mut Snake) {
     // Drain all pending events, apply the latest direction
     loop {
-        let _ = syscall::send(INPUT_EP, 0, 0, 0, 0);
-        let (tag, kind, _, _) = syscall::receive(INPUT_EP);
+        let Ok([tag, kind, _, _]) = syscall::request(INPUT_EP, [0; 4]) else {
+            break;
+        };
         if tag == 0 { break; } // NoEvent — queue drained
         if tag == 1 {
             match kind {