Fix: rejoining stacked players on top of each other (one fell through)

All players spawned at the exact same PlayerSpawn point and were on the
same collision layer, so two overlapping CharacterBody3Ds triggered a
physics depenetration shove that could launch one through the 1-unit-thick
floor.

- server.gd: golden-angle spawn spread -- each join lands ~1m+ from the
  others, growing outward, never exactly repeating.
- server_player.tscn + player.tscn: players on collision layer 2, mask 1
  (world only) -- players no longer collide with each other at all
  (fine for a social game; also removes the shove).
- player_spawner.gd + player.gd: hard safety net -- if y < -10 (any
  tunnel-through), snap back to the spawn instead of falling forever.

Verified: 3 server players spawn 1.15m+ apart, none fall, all rest on the
floor. 2p multiplayer + network_client smokes green.

Client-side -- rebuild the exe.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scenes/player.tscn

@@ -11,6 +11,8 @@ radius = 0.35
 height = 1.6
 
 [node name="Player" type="CharacterBody3D"]
+collision_layer = 2
+collision_mask = 1
 script = ExtResource("1_player")
 
 [node name="CollisionShape3D" type="CollisionShape3D" parent="."]

scenes/server_player.tscn

@@ -7,6 +7,8 @@ radius = 0.35
 height = 1.6
 
 [node name="Player" type="CharacterBody3D"]
+collision_layer = 2
+collision_mask = 1
 script = ExtResource("1")
 
 [node name="CollisionShape3D" type="CollisionShape3D" parent="."]

scripts/player.gd

@@ -26,6 +26,7 @@ const MOUSE_SENSITIVITY: float = 0.003
 
 var _input_direction := Vector2.ZERO
 var _camera_pitch: float = -0.12
+var _spawn_position: Vector3 = Vector3(0, 1.5, 0)
 
 ## Vertical offset applied to the assembled avatar so its feet (origin y=0)
 ## line up with the bottom of the player's collision capsule.
@@ -69,6 +70,7 @@ func _ready() -> void:
 	else:
 		push_warning("player.gd: no PlayerSpawn marker found; spawning at origin")
 		global_position = Vector3(0, 1.0, 0)
+	_spawn_position = global_position
 
 	# The spring arm must not collide with the player's own capsule (they're
 	# on the same layer), or the camera gets yanked right up against the
@@ -192,6 +194,11 @@ func _physics_process(delta: float) -> void:
 
 	move_and_slide()
 
+	# Safety net -- never fall forever if something goes wrong.
+	if global_position.y < -10.0:
+		global_position = _spawn_position
+		velocity = Vector3.ZERO
+
 	net_input = {
 		"move_x": direction.x, "move_z": direction.z,
 		"jump": jumped, "look_yaw": rotation.y,

scripts/player_spawner.gd

@@ -14,6 +14,10 @@ const GRAVITY := 9.8
 
 var peer_id: int = -1
 
+## Where the server spawned this player (set by server.gd). Used as the
+## respawn point if the player somehow ends up below the world.
+var spawn_position: Vector3 = Vector3(0, 1.5, 0)
+
 ## Highest input seq applied authoritatively so far (echoed in snapshots so
 ## the client can drop acked inputs and replay the rest).
 var last_applied_seq: int = 0
@@ -38,6 +42,13 @@ func _physics_process(delta: float) -> void:
 
 	rotation.y = _look_yaw
 
+	# Safety net: if a player ends up below the world (physics shove, tunnel
+	# through the floor), put them back on their spawn instead of falling
+	# forever.
+	if global_position.y < -10.0:
+		global_position = spawn_position
+		velocity = Vector3.ZERO
+
 
 func _integrate(move_x: float, move_z: float, jump: bool, delta: float) -> void:
 	if not is_on_floor():

scripts/server.gd

@@ -30,6 +30,9 @@ var status_file_path: String = ""
 var players: Dictionary = {}
 var tick: int = 0
 var is_running: bool = false
+## Monotonic count of joins ever -- drives spawn spread so two players never
+## land on the same spot (which used to shove one through the floor).
+var _join_count: int = 0
 
 var _player_scene: PackedScene = preload("res://scenes/server_player.tscn")
 var _level_scene: PackedScene = preload("res://scenes/worlds/test_level.tscn")
@@ -65,6 +68,16 @@ func _ready() -> void:
 	print("[Server] world=%s listening on ENet %d (%d Hz)" % [world_id, port, PHYSICS_HZ])
 
 
+## A spawn point offset from the level's marker so joins don't stack. Golden-
+## angle spiral: evenly spread, never exactly repeats, grows slowly outward.
+func _spawn_for(index: int) -> Vector3:
+	if index == 0:
+		return _spawn_point
+	var angle := index * 2.399963  # golden angle (radians)
+	var radius := 0.9 + 0.25 * float(index)
+	return _spawn_point + Vector3(cos(angle) * radius, 0.0, sin(angle) * radius)
+
+
 func _parse_args() -> void:
 	var args := OS.get_cmdline_user_args()
 	var i := 0
@@ -127,7 +140,10 @@ func _on_peer_connected(peer_id: int) -> void:
 	player.name = "Player_%d" % peer_id
 	player.peer_id = peer_id
 	add_child(player)
-	player.global_position = _spawn_point
+	var spawn := _spawn_for(_join_count)
+	_join_count += 1
+	player.global_position = spawn
+	player.spawn_position = spawn
 	players[peer_id] = player
 	print("[Server] peer %d joined (%d players)" % [peer_id, players.size()])
 	_write_status()