The bug

I expected to be able to replace the player's mainhand when the consume_item trigger runs. Instead the item gets replaced by what would've been the resulting item after consuming.

How to reproduce

1. Have an advancement that runs a function every time the player consumes an item

   {
     "criteria": {
       "requirement": {
         "trigger": "minecraft:consume_item"
       }
     },
     "rewards": {
       "function": "test:consume_item"
     }
   }

2. Create a function that replaces the mainhand with an apple

   advancement revoke @s only test:consume_item
   replaceitem entity @s weapon.mainhand apple

3. Take a stack of bread and eat it in survival
4. You briefly see the item, but then it gets replaced by 63 bread