Co-op pass: host-disconnect handling, spectate, late-join wave sync

- Clients now handle the host closing the arena: bank winnings if
  still alive (retire), reset the HUD, and return to the camp menu
  instead of being stranded in a dead world
- Death in co-op offers Spectate when a teammate is still fighting:
  closes the results overlay and watches the run; the escape menu
  gains a "Back to Camp" option for dead spectators to leave later
- Late joiners receive the current wave number on connect so their
  HUD doesn't sit on "Prepare..." until the next wave starts

level/ui/scripts/escape_menu.gd

@@ -54,14 +54,19 @@ func toggle_menu():
 		if player and player.is_multiplayer_authority():
 			Input.mouse_mode = Input.MOUSE_MODE_CAPTURED
 
-## Retiring is only possible while alive with an active run
+## Alive with an active run: retire (bank winnings).
+## Dead but spectating a live session: plain trip home (settlement already done).
 func _update_retire_button():
 	if not _retire_button:
 		return
-	var can_retire = GameState.run_active and player and not player.is_dead
-	_retire_button.visible = can_retire
-	if can_retire:
+	if GameState.run_active and player and not player.is_dead:
+		_retire_button.visible = true
 		_retire_button.text = "Retire to Camp (+%dg)" % GameState.run_gold
+	elif multiplayer.multiplayer_peer != null and player and player.is_dead:
+		_retire_button.visible = true
+		_retire_button.text = "Back to Camp"
+	else:
+		_retire_button.visible = false
 
 ## Called when Resume button is clicked
 func _on_resume_pressed():