Does Gust take effect before Assault (e.g., when Vayne attacks)?

Ruling: No, Gust does not take effect before Assault. Assault is a passive ability that turns on immediately when a unit is designated as an attacker, which happens during cleanup after a move ends, before there are any opportunities to cast spells like Gust.

Sequence:

• Unit moves to an enemy-occupied battlefield
• Battlefield becomes contested when the unit arrives
• Cleanup begins at the end of the move
• Attacker and Defender designations are assigned during cleanup
• Assault and Shield turn on immediately upon designation
• Cleanup completes (including marking Combat as pending)
• Combat begins with Showdown
• Showdown has an Initial Chain where "When I Attack" and "When I Defend" triggers occur

Nuances:

• Assault and Shield are passive abilities (always on/off based on designation), not triggers
• Triggers are identifiable by the word "When" (like "When I Attack" or "When I Defend")
• Spells like Gust only have opportunities to be cast after cleanup completes