Keep a move behind a dig and its arm swing for the next tick

The hub hands a dig (handlePlayerAction) to the game after its pass, and
a move queued right behind it waited for the next tick so it was not
checked against the block the player had just broken. A creative break
sends the arm swing (Punch) between the dig and the move, so the move
was handled in the same pass: the block was still there, the move was
refused and the player sent back. Digging straight down, the player
sank into the block, was put back on top of it a tick later, then fell.

Any move left in the queue now waits, with what is queued before it,
as vanilla handles the packets in order. Traced with horizon-ctl in a
creative world: the player rose back after 6 to 7 of 8 breaks before,
after none now.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client/src/lan/hub.rs

@@ -2216,13 +2216,16 @@ impl Hub {
                 // game's, run after this pass. A move queued behind it is checked
                 // against the block the player just broke and falls through, so it
                 // would be sent back; it waits for the next tick, when the block is
-                // gone, as vanilla handles the two packets in order.
+                // gone, as vanilla handles the packets in order. So does everything
+                // queued before that move: the arm swing (Punch) comes between the dig
+                // and the move.
                 S::PlayerAction(p) if p.action <= 3 => {
                     events.push(HostEvent::Packet(conn, Box::new(S::PlayerAction(p))));
-                    if matches!(
-                        self.guests[i].inbox.front(),
-                        Some(S::MovePlayerPos(_) | S::MovePlayerPosRot(_))
-                    ) {
+                    if self.guests[i]
+                        .inbox
+                        .iter()
+                        .any(|p| matches!(p, S::MovePlayerPos(_) | S::MovePlayerPosRot(_)))
+                    {
                         break;
                     }
                 }

crates/horizon-client/tests/lan_bot.rs

@@ -407,6 +407,54 @@ fn sprint_commands_survive_keyboard_input_changes() {
     );
 }
 
+#[test]
+fn a_move_behind_a_dig_and_its_swing_waits_for_the_next_tick() {
+    let Some(resources) = resources() else {
+        return;
+    };
+    let mut s = server(&resources);
+    let port = s.hub.lan.port;
+    let _bot = run(&mut s, move || connect(port, "Digger", true));
+    let deadline = Instant::now() + Duration::from_secs(5);
+    while s.hub.guests.is_empty() {
+        s.tick(&[]);
+        assert!(Instant::now() < deadline, "guest did not join");
+        thread::yield_now();
+    }
+    s.hub.guests[0].loaded = true;
+    let at = s.hub.guests[0].position;
+    let below = [
+        at[0].floor() as i32,
+        at[1].floor() as i32 - 1,
+        at[2].floor() as i32,
+    ];
+    // A creative break as the client sends it in one tick: the dig, the arm swing,
+    // then the move into the block it predicted gone.
+    let inbox = &mut s.hub.guests[0].inbox;
+    inbox.push_back(S::PlayerAction(play::PlayerAction {
+        action: 0,
+        pos: below,
+        direction: 1,
+        sequence: 1,
+    }));
+    inbox.push_back(S::Punch(Empty));
+    inbox.push_back(S::MovePlayerPos(play::MovePlayerPos {
+        x: at[0],
+        y: at[1] - 0.0784,
+        z: at[2],
+        flags: 0,
+    }));
+    s.tick(&[]);
+    // The game breaks the block after the hub's pass: the move waits, or it would be
+    // checked against the block and sent back.
+    let g = &s.hub.guests[0];
+    assert_eq!(g.position, at, "the move was handled before the dig");
+    assert!(
+        matches!(g.inbox.back(), Some(S::MovePlayerPos(_))),
+        "the move left the queue"
+    );
+}
+
 #[test]
 fn status_and_join() {
     let Some(resources) = resources() else {