send the battle state five times a second

the server was simulating correctly all along - the log shows a goblin
covering 120 units a tick and a knight 60, exactly their Speed columns,
in a straight line with no jitter. the teleporting was the correction
rate: one snapshot a second, while the client runs its own prediction in
between and diverges from ours. a unit gets more than a tile out of step
before our state arrives and drags it back.

the snapshot now goes every four ticks and the gateway ticks every fifty
milliseconds rather than two hundred, so a correction moves a unit a
fifth as far.

this makes the symptom smaller, not absent. it goes away when the two
simulations agree, which is what the checksum comparison is for and what
collisions and projectiles are still missing for.

crates/game-service/src/battle_session.rs

@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 use std::sync::Arc;
-pub const SNAPSHOT_INTERVAL_TICKS: i32 = 20;
+pub const SNAPSHOT_INTERVAL_TICKS: i32 = 4;
 pub const MAX_CATCH_UP_TICKS: i32 = 40;
 use std::time::Instant;
 use logic::battle::{
@@ -106,11 +106,20 @@ impl BattleSession {
     fn snapshot_message(&mut self) -> Option<WireMessage> {
         let snapshot = self.mode.snapshot().ok()?;
         let report = verify_snapshot(&snapshot);
+        let unit = self
+            .mode
+            .battle
+            .objects
+            .objects
+            .iter()
+            .find(|entry| entry.stats().speed > 0)
+            .map(|entry| (entry.position(), entry.owner_index()));
         tracing::debug!(
             tick = self.tick,
             bytes = snapshot.len(),
             ok = report.is_ok(),
-            "built a battle snapshot"
+            unit = ?unit,
+            "battle snapshot"
         );
         if !report.is_ok() {
             tracing::error!(

crates/gateway/src/message_manager.rs

@@ -22,7 +22,7 @@ pub enum RoutingError {
     Unauthenticated(u16),
 }
 type RoutingResult<T> = Result<T, RoutingError>;
-pub const BATTLE_TICK_INTERVAL: Duration = Duration::from_millis(200);
+pub const BATTLE_TICK_INTERVAL: Duration = Duration::from_millis(50);
 pub struct MessageManager {
     peer: SocketAddr,
     config: Arc<GatewayConfig>,