Stalwart foundation says:
“When you take physical damage, always reduce it by your armor score before applying it to your thresholds. You can still spend armor slots to reduce it further.”
And the I Am Your Shield Domain card says:
“When an ally very close to you is going to take damage, you may mark a stress to stand in its way and take the damage instead. Reduce the damage by a value equal to your Strength Trait. You may also reduce the damage by spending armor slots.”
When you use I am your Shield you mark a stress, take the damage instead of your ally and reduce it by your Strength trait, can you also use the Stalwart foundation in combination and also reduce the incoming damage by your armor score before applying it to your threshold, since it says you always do it? Or they are mutually exclusive?