EconomyShop v1.0.3.4 — Patch Notes
Critical Bug Fixes

Selling Air / Invalid Items

• Players could sell AIR or null-material items for money. Added isAir() and null checks in handleQuickSell, executeSell, and the material browser. Inventory counting now skips air stacks. Blacklisted materials are also now blocked when adding items via the material browser.

Sell Multiplier Creating Free Money

• All config values that feed into price math are now clamped to safe bounds — sell-price-multiplier locked to [0.01, 1.0], buy-sell-spread to [0.01, 1.0], all stock settings floored at 1. Prevents misconfiguration from generating money.
• Fixed NaN and Infinity multipliers caused by division-by-zero when stock reached 0. getEffectiveSellPrice and getEffectiveBuyPrice now treat NaN/Infinity as 1.0. DynamicPricingEngine uses Math.max(1, ...) on every stock divisor.
• getEffectiveSellPrice now returns 0 instead of null when an item has no sell price set.

Money Duplication via Transaction Order

• Reversed sell operation order: items are now removed from inventory before depositing money. Previously, a crash between deposit and item removal would give money without taking items.
• Added dupe detection: item count is verified before and after removal. If the delta doesn't match the expected quantity, the transaction aborts, items are returned, and a [DUPE DETECTION] warning is logged.

Other Changes

• Sell confirmation GUI now driven by sell-confirmation.yml layout instead of hardcoded slots
• Sell-to-shop GUI: left-click quick-sells all of that item, shift+left-click opens quantity selector, right-click excludes items from "Sell All"
• InventoryDragEvent now also sets Result.DENY (not just setCancelled)
• DynamicPricingEngine.getOrCreateState uses ConcurrentHashMap.computeIfAbsent (atomic, replaces check-then-put)