adds /atom/proc/get_mob_owner() + blocks a delayed possession of item that's possessed by a player already

code/__HELPERS/atoms.dm

@@ -350,3 +350,18 @@ B --><-- A
 		return get_step(ref, base_dir)
 
 */
+
+/// returns a mob that possesses this atom(usually item),
+/// or returns null if it is possessed by no mob.
+/atom/proc/get_mob_loc(as_first_mob=TRUE)
+	var/atom/upper = src
+	var/final_mob
+	while(upper)
+		upper = upper.loc
+		if(ismob(upper))
+			final_mob = upper
+			// if this is TRUE, it will immediately return a mob that holds the atom
+			// if this is FALSE, it will find a final mob when it's chain-contained (i.e. mob in mob in mob...)
+			if(as_first_mob)
+				return final_mob
+	return final_mob

code/modules/clothing/chameleon.dm

@@ -309,14 +309,7 @@
 /datum/action/item_action/chameleon/change/proc/update_mob_hud(atom/card_holder)
 	// we're going to find a human, and store human ref to 'card_holder' by checking loc multiple time.
 	if(!ishuman(card_holder))
-		if(!card_holder)
-			card_holder = target.loc
-		if(istype(card_holder, /obj/item/storage/wallet))
-			card_holder = card_holder.loc // this should be human
-		if(istype(card_holder, /obj/item/computer_hardware/card_slot))
-			card_holder = card_holder.loc
-			if(istype(card_holder, /obj/item/modular_computer/tablet))
-				card_holder = card_holder.loc // tihs should be human
+		card_holder = target.get_mob_loc()
 	if(!ishuman(card_holder))
 		return
 	var/mob/living/carbon/human/card_holding_human = card_holder

code/modules/mob/inventory.dm

@@ -161,7 +161,7 @@
 /mob/proc/can_equip(obj/item/I, slot, disable_warning = FALSE, bypass_equip_delay_self = FALSE)
 	return FALSE
 
-/mob/proc/can_put_in_hand(I, hand_index)
+/mob/proc/can_put_in_hand(atom/I, hand_index)
 	if(hand_index > length(held_items))
 		return FALSE
 	if(!put_in_hand_check(I))
@@ -209,7 +209,12 @@
 	return FALSE
 
 //Puts the item into our active hand if possible. returns TRUE on success.
-/mob/proc/put_in_active_hand(obj/item/I, forced = FALSE, ignore_animation = TRUE)
+/mob/proc/put_in_active_hand(obj/item/I, forced = FALSE, ignore_animation = TRUE, checks_mob_loc=TRUE)
+	if(checks_mob_loc) // checks if it's possessed by a mob to prevent client delay. offer code sends this as FALSE.
+		var/owner = I.get_mob_loc()
+		if(ismob(owner) && owner != src)
+			show_message("<span class='notice'>You wanted to pick up [src], but it's already on someone's hand. You feel bad about the space latency...</span>")
+			return FALSE // sorry, you won't get the benefit of your bad latency.
 	return put_in_hand(I, active_hand_index, forced, ignore_animation)
 
 
@@ -221,7 +226,7 @@
 //Puts the item our active hand if possible. Failing that it tries other hands. Returns TRUE on success.
 //If both fail it drops it on the floor and returns FALSE.
 //This is probably the main one you need to know :)
-/mob/proc/put_in_hands(obj/item/I, del_on_fail = FALSE, merge_stacks = TRUE, forced = FALSE)
+/mob/proc/put_in_hands(obj/item/I, del_on_fail = FALSE, merge_stacks = TRUE, forced = FALSE, checks_mob_loc = TRUE)
 	if(QDELETED(I))
 		return FALSE
 
@@ -245,7 +250,7 @@
 						to_chat(usr, "<span class='notice'>Your [inactive_stack.name] stack now contains [inactive_stack.get_amount()] [inactive_stack.singular_name]\s.</span>")
 						return TRUE
 
-	if(put_in_active_hand(I, forced))
+	if(put_in_active_hand(I, forced, checks_mob_loc=checks_mob_loc))
 		return TRUE
 
 	var/hand = get_empty_held_index_for_side("l")

code/modules/mob/living/carbon/inventory.dm

@@ -355,4 +355,4 @@
 		return
 	visible_message("<span class='notice'>[src] takes [I] from [offerer]</span>", \
 					"<span class='notice'>You take [I] from [offerer]</span>")
-	put_in_hands(I)
+	put_in_hands(I, checks_mob_loc=FALSE)