fix(items): defer empty draw when slot reads nil after lag

Under server lag BAG_UPDATE can fire before item data arrives, causing
GetContainerItemInfo to return nil for a still-occupied slot and Bagnon
to broadcast ITEM_SLOT_UPDATE with no link — the slot then renders empty
until the next bag event. UpdateItem now queues a single ~0.25s retry
for the bag when a previously occupied slot reads nil; the retry pass
trusts whatever it reads, so genuine empties still resolve.

Bagnon/utility/itemEvents.lua

@@ -45,6 +45,7 @@ Bagnon.BagEvents = BagEvents
 
 local slots = {}
 local bagTypes = {}
+local pendingBags = {}
 
 local function ToIndex(bag, slot)
 	return (bag < 0 and bag*100 - slot) or bag*100 + slot
@@ -54,6 +55,29 @@ local function GetBagSize(bag)
 	return (bag == KEYRING_CONTAINER and GetKeyRingSize()) or GetContainerNumSlots(bag)
 end
 
+-- Defers a re-check of a bag by ~0.25s; used when a previously occupied slot
+-- reads back nil (lag race between BAG_UPDATE and item data arriving).
+local retryFrame = CreateFrame('Frame')
+retryFrame.elapsed = 0
+retryFrame:Hide()
+retryFrame:SetScript('OnUpdate', function(self, elapsed)
+	self.elapsed = self.elapsed + elapsed
+	if self.elapsed < 0.25 then return end
+	self.elapsed = 0
+	self:Hide()
+	local bags = pendingBags
+	pendingBags = {}
+	for bag in pairs(bags) do
+		Bagnon.BagEvents:UpdateItems(bag, true)
+	end
+end)
+
+local function scheduleRetry(bag)
+	pendingBags[bag] = true
+	retryFrame.elapsed = 0
+	retryFrame:Show()
+end
+
 
 --[[ Startup ]]--
 
@@ -110,7 +134,7 @@ function BagEvents:RemoveItem(bag, slot)
 	end
 end
 
-function BagEvents:UpdateItem(bag, slot)
+function BagEvents:UpdateItem(bag, slot, isRetry)
 	local data = slots[ToIndex(bag, slot)]
 
 	if data then
@@ -121,6 +145,14 @@ function BagEvents:UpdateItem(bag, slot)
 		local start, duration, enable = GetContainerItemCooldown(bag, slot)
 		local onCooldown = (start > 0 and duration > 0 and enable > 0)
 
+		-- A previously occupied slot reading back nil is usually a lag race between
+		-- BAG_UPDATE and item data arriving from the server. Defer once before drawing
+		-- the slot as empty; on the second pass we trust whatever we read.
+		if prevLink and (not link) and (not isRetry) then
+			scheduleRetry(bag)
+			return
+		end
+
 		if not(prevLink == link and prevCount == count) then
 			data[1] = link
 			data[2] = count
@@ -132,9 +164,9 @@ function BagEvents:UpdateItem(bag, slot)
 	end
 end
 
-function BagEvents:UpdateItems(bag)
+function BagEvents:UpdateItems(bag, isRetry)
 	for slot = 1, GetBagSize(bag) do
-		self:UpdateItem(bag, slot)
+		self:UpdateItem(bag, slot, isRetry)
 	end
 end