I just a unit before defend and attack trigger?

Whether or not you can play Gust before "When I attack" or "When I defend" triggers depends on whether the unit's arrival at the battlefield triggers a combat or non-combat showdown.

According to RiftJudge FAQ #3118 and FAQ #3218, the state of the battlefield at the time of arrival determines your priority window.

When you CAN play Gust (Before Triggers)

If a unit moves to an empty battlefield, this initiates a non-combat showdown.

1. Open Showdown Window: The game enters an "Open State" showdown. Because there is no chain yet, you have the priority to play Gust.
2. Resolution: If you play Gust now, it resolves. If the unit is returned to the owner's hand, it is removed from the battlefield.

When you CANNOT play Gust (Before Triggers)

If a unit moves to an occupied battlefield (one that already contains units controlled by the opposing player), a combat showdown begins immediately.

1. Initial Chain: Under the rules for combat, designations (Attacker/Defender) are established as the first task.
2. Trigger Placement: Once designations are established, any "When I attack" or "When I defend" triggers are immediately placed on the chain as "Pending Items" (Rule 459.2.d).
3. Closed State: Once these triggers are on the chain, the state becomes "Closed." You cannot play Gust until you first react to the triggered abilities on the chain, or wait for them to resolve and the state to return to "Open." In this scenario, the triggers have already been successfully placed on the chain before you have an opportunity to Gust the unit.

Summary

• Moving to an empty battlefield: Yes, you can play Gust during the open showdown window.
• Moving to an occupied battlefield: No, the combat designations and triggers occur as the combat opens, forcing the state to "Closed" before you gain a priority window to cast Gust.

This interpretation is based on the distinction between non-combat showdowns and combat showdowns (where the state is closed by triggered abilities) described in RiftJudge FAQ #3118 and Rule 459.

Note: I could not fully verify this ruling against the retrieved rules.