If card text has an effect when the card is destroyed, that’s an interrupt. It activates before the card is actually destroyed. Akash'Bhuta’s armor makes her damage herself when it’s destroyed, but since the armor is still in play, she still gets damage reduction from it.
If card text has an effect when the card is damaged, that’s not an interrupt. Captain Cosmic can put out a construct that heals an ally when it’s damaged. If it takes enough damage to destroy it, it goes straight to the trash, no healing provided.
Either of these rulings would make sense alone, but they seem silly side by side.