How does Sanctuary interact with "reflected" damage?

Question

Through a peculiar course of events with a touch of homebrew, my cleric got to learn the spell Armor of Agathys (Player's Handbook p. 215) which has the effect:

If a creature hits you with a melee attack ... the creature takes 5 cold damage.

As a regular user of the Sanctuary spell, I wondered how these spells would interact in the following situation:

1. Casting Sanctuary on myself as soon as fight starts
2. Casting Armor of Agathys to add an additional defense
3. A goblin succeeds the Sanctuary saving throw and hits me with a melee attack
4. The goblin takes damage due to Armor of Agathys.

Does the Sanctuary spell end because I casted Armor of Agathys and after Sanctuary and the spell affects the goblin when it takes damages ?

Would Sanctuary end if I were to cast Armor of Agathys 10 mins ago because this dark and shadowy dungeon looked dangerous ?

Would Sanctuary break if the damage reflection came from the effect of a racial trait or a kinda spiky enchanted armour ?

Answer 1

Sanctuary breaks in all those cases

The Errata (v. 2.0, 2018) has changed the last sentence of sanctuary to :

If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends. (emphasis mine)

Thus it does not matter when you cast armor of Agathys. If it triggers and deals damage to a creature, it will violate the terms of sanctuary and cause it to end. The same would be true for other sources of damage too that originate from you (including from your equipment).