M1b: survival stats, day/night, fire fuel, cooking, foraging, torches, death + grave

- Health, stamina, hunger, warmth and wet with HUD bars, status tags and clock
- 20-minute day/night cycle with moon, stars and lit clouds
- Campfire fuel (2 min start, 15 min max), heat radius, cooking needs a lit fire
- Berry bushes (regrow 10 min), mushrooms, roasted mushroom, torch
- Stamina costs for sprint, jump and harvest hits
- Death respawns at island start and leaves a grave bag
- Saves include stats, time of day, fire fuel, regrowth timers and graves
- New test_survival_stats suite; tests fail if a script error aborts them

scripts/ui/inventory_screen.gd

@@ -132,7 +132,7 @@ func close() -> void:
 		if left > 0 and container != null:
 			left = container.inventory.add(_cursor.id, left)
 		_cursor = null
-	if container != null and container.inventory.changed.is_connected(_refresh):
+	if container != null and is_instance_valid(container) and container.inventory.changed.is_connected(_refresh):
 		container.inventory.changed.disconnect(_refresh)
 	container = null
 	visible = false
@@ -147,12 +147,17 @@ func _input(event: InputEvent) -> void:
 		get_viewport().set_input_as_handled()
 	elif event is InputEventMouseMotion:
 		_cursor_view.global_position = event.position
-	# Walking away from a chest closes it.
-	if container != null and player.global_position.distance_to(container.global_position) > 5.0:
-		close()
+
 
 func _process(_d: float) -> void:
-	if visible and container != null and player.global_position.distance_to(container.global_position) > 5.0:
+	if not visible or container == null:
+		return
+	# Containers can vanish while open (an emptied grave crumbles).
+	if not is_instance_valid(container) or container.is_queued_for_deletion():
+		container = null
+		_rebuild_chest()
+		return
+	if player.global_position.distance_to(container.global_position) > 5.0:
 		close()
 
 func _rebuild_chest() -> void:
@@ -177,7 +182,7 @@ func _on_player_slot(i: int, right: bool, shift: bool) -> void:
 	_refresh()
 
 func _on_chest_slot(i: int, right: bool, shift: bool) -> void:
-	if not Actions._in_reach(player, container, 1.0):
+	if container == null or not is_instance_valid(container) or not Actions._in_reach(player, container, 1.0):
 		return
 	if shift:
 		Actions.transfer(player, container.inventory, i, player.inventory, container)