Bank: a full stack spills into another slot

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

game.py

@@ -718,12 +718,19 @@ def stack_size(world: dict) -> int:
     return BASE_STACK + 250 * building_level(world, "storehouse")
 
 
+def slots_used(world: dict, player: dict) -> int:
+    """Bank slots taken: an item spills into another slot every full stack."""
+    stack = stack_size(world)
+    return sum(-(-qty // stack) for qty in player["bank"].values())
+
+
 def bank_room(world: dict, player: dict, item: str) -> int:
-    """How many more of `item` fit in the bank."""
+    """How many more of `item` fit: the rest of its last stack, plus any free slots."""
+    stack = stack_size(world)
     have = player["bank"].get(item, 0)
-    if have == 0 and len(player["bank"]) >= bank_slots(world, player):
-        return 0
-    return max(0, stack_size(world) - have)
+    partial = -have % stack  # room left in the item's last, part-filled stack
+    free = max(0, bank_slots(world, player) - slots_used(world, player))
+    return partial + free * stack
 
 
 def city_uses(item: str) -> list[str]: