Can I gust a unit back before Mask of Foresight trigger resolve?

Yes, you can use Gust as a reaction to Mask of Foresight's triggered ability before the trigger resolves.

According to RiftJudge FAQ #4305:

• When a unit attacks alone, the Mask of Foresight triggered ability is placed on the chain.
• Because triggered abilities use the chain, the defender has priority to play reactions before the trigger resolves.
• If you play Gust as a reaction to that trigger, it will resolve first, returning the unit to its owner's hand before Mask of Foresight's effect can apply.

Sequence:

1. Unit attacks/defends: The unit gains the designation, and Mask of Foresight triggers.
2. Chain State: The Mask of Foresight ability is added to the chain (CLOSED state).
3. Reaction: The defender plays Gust in response to the trigger.
4. Resolution (LIFO - Last In, First Out):
   • Gust resolves first, returning the unit to its owner's hand.
   • Mask of Foresight attempts to resolve next. Since the target unit is no longer on the battlefield, the instruction to give it +1 Might will fail (it will mistarget), and the ability will have no effect.