Does Grafdigger's Cage stop cards from being cast from exile with an impulse draw effect?

Grafdigger's Cage states that players can't cast cards from exile. Impulse draw effects (like those from Light Up the Stage or Valiant Veteran-style abilities) exile cards and allow you to play them until end of turn — but Grafdigger's Cage shuts this down entirely for spells (non-land cards that would be cast).

Under CR 601.1, casting a spell means taking a card from wherever it is and placing it on the stack. Grafdigger's Cage creates a replacement/restriction effect that forbids this action when the card's origin zone is exile. The exile zone is still a zone (CR 406), and cards exiled by impulse effects are still in exile when you attempt to cast them.

Note that Grafdigger's Cage does not stop you from playing a land card exiled by an impulse effect, because playing a land is not casting a spell (CR 305.1). Only the casting of spells from exile is blocked.

Example: You cast Light Up the Stage and exile two cards — a Mountain and a Lightning Bolt. You may still play the Mountain (it's not cast), but you cannot cast Lightning Bolt from exile because Grafdigger's Cage prohibits it.

This interaction is well-established in competitive play. Grafdigger's Cage is frequently used as a hate piece specifically to nullify impulse-draw spells in formats like Modern and Legacy.