Makes Client/Mob Login/out behavior match BYOND way more closely

DMCompiler/DMStandard/Types/Atoms/Mob.dm

@@ -16,5 +16,10 @@
 	layer = MOB_LAYER
 
 	proc/Login()
+		if(!loc)
+			var/turf/fallback_spawn = locate(1, 1, 1) // TODO: Find nearest non-dense turf
+			if(fallback_spawn)
+				loc = fallback_spawn
 
 	proc/Logout()
+		del client

DMCompiler/DMStandard/Types/Client.dm

@@ -63,10 +63,11 @@
 				break
 
 		if (mob == null) // No existing mob, create a default one
-			mob = new world.mob(locate(1,1,1)) // TODO: Find nearest non-dense turf
-
-		eye = mob
-		statobj = mob
+			var/mob/initial_mob = new world.mob()
+
+			eye = initial_mob
+			statobj = initial_mob
+			mob = initial_mob
 		return mob
 
 	proc/Del()

OpenDreamRuntime/DreamConnection.cs

@@ -37,32 +37,20 @@ public sealed partial class DreamConnection {
     [ViewVariables] public DreamObjectMob? Mob {
         get => _mob;
         set {
-            if (_mob != value) {
-                var oldMob = _mob;
-                value?.IncRef();
-                _mob?.DecRef();
-                _mob = value;
-
-                if (oldMob != null) {
-                    oldMob.Key = null;
-                    oldMob.Connection = null;
-                    oldMob.SpawnProc("Logout").Dispose();
-                }
-
-                StatObj = new(value);
-                if (Eye != null && Eye == oldMob) {
-                    Eye = value;
-                }
+            if (_mob == value)
+                return;
 
-                if (_mob != null) {
-                    // If the mob is already owned by another player, kick them out
-                    _mob.Connection?.Mob = null;
+            var oldMob = _mob;
+            var oldConnection = value?.Connection;
+            SetClientMob(value);
 
-                    _mob.Connection = this;
-                    _mob.Key = Key;
-                    _mob.SpawnProc("Login", usr: _mob).Dispose();
-                }
+            if(oldConnection is not null) {
+                oldConnection.Client?.Delete();
+                _mob!.SpawnProc("Logout").Dispose();
             }
+
+            oldMob?.SpawnProc("Logout").Dispose();
+            _mob?.SpawnProc("Login", usr: _mob).Dispose();
         }
     }
 
@@ -125,21 +113,43 @@ public void HandleDisconnection() {
         _verbSystem?.RemoveConnectionFromRepeatingVerbs(this);
         Session = null;
 
-        if (_mob != null) {
-            // Don't null out the ckey here
-            _mob.SpawnProc("Logout").Dispose();
-
-            if (_mob != null) { // Logout() may have removed our mob
-                _mob.Connection = null;
-                _mob = null;
-            }
-        }
-
+        Mob = null;
         Client.DecRef();
         Client.Delete();
         Client = null;
     }
 
+    /// <summary>
+    /// Sets the <see cref="Mob">connection's mob</see> without any side effects.
+    /// </summary>
+    private void SetClientMob(DreamObjectMob? newMob) {
+        if(newMob == _mob)
+            return;
+
+        var oldMob = _mob;
+        _mob = newMob;
+        newMob?.IncRef();
+        oldMob?.DecRef();
+
+        if (oldMob is not null) {
+            oldMob.Key = null;
+            oldMob.Connection = null;
+        }
+
+        StatObj = new(newMob);
+        if (Eye is not null && Eye == oldMob) {
+            Eye = newMob;
+        }
+
+        if (newMob is not null) {
+            // If the mob is already owned by another player, kick them out
+            newMob.Connection?.SetClientMob(null);
+
+            newMob.Connection = this;
+            newMob.Key = Key;
+        }
+    }
+
     public void UpdateStat() {
         if (Session == null || Client == null || _currentlyUpdatingStat)
             return;