2011-06-01

Caged Sun’s triggered ability is a mana ability, which means the ability doesn’t use the stack and can’t be responded to.

2022-06-10

An ability that triggers from the resolution of an activated mana ability is also a mana ability. This means that if the land's ability that caused you to add mana was an activated mana ability, Caged Sun's triggered ability won't use the stack and can't be responded to.