If a Goliath is hit by an attack, they have resistance to its damage type, and they also use Stone's Endurance, in what order is the damage reduced?

Question

Let's suppose we have a raging Goliath Barbarian. They are hit by an attack that deals 36 slashing damage, and then, as a reaction, they use Stone's Endurance. Since they are raging, they have resistance to that damage type, so it should be halved. In this case, how would the damage be reduced? Would the resistance or the racial feature be applied first?

Considering they roll a 7 on the d12 + 3 (its CON modifier), I can imagine the following two options:

First case scenario, the resistance is applied first, reducing the damage from 36 to 18. It is then subtracted by 10 because of its racial feature, resulting in 8 slashing damage taken.

Second case scenario, it first subtracts 10 from the total 36 slashing damage, resulting in 26. The damage is then halved because of their resistance, which ends up being 13 slashing damage taken.

Answer 1

Resistance is always applied after all other modifiers to damage.

The rules for "Damage Resistance and Vulnerability" state:

Resistance and then vulnerability are applied after all other modifiers to damage.

Stone's Endurance is a modifier to the damage:

When you take damage, you can use your reaction to roll a d12. Add your Constitution modifier to the number rolled and reduce the damage by that total.

So resistance is applied after Stone's Endurance.

The goliath takes 36 damage of a type they are resistant to. Using Stone's Endurance reduces the damage from 36 to 26, then resistance reduces the damage from 26 to 13, which is the second scenario described in your question.

Answer 2

Stone's Endurance applies "when you take damage" not before

From the general rules, Hit Points

Whenever a creature takes damage, that damage is subtracted from its hit points

and Damage Rolls:

You roll the damage die or dice, add any modifiers, and apply the damage to your target.

So, first you calculate the damage, and then you take it. And you can use Stone's Endurance "When you take damage" not before.

If you try it the other way you and use Stone's Endurance to reduce damage to 0, so you take no damage, so you can not use Stone's Endurance, so you take the damage...