When can you play a +1 might reaction like En Garde to save a unit from Disintegrate's lethal damage?

Ruling: You can only play En Garde before Disintegrate resolves. Once Disintegrate resolves and deals lethal damage, a cleanup occurs immediately and there is no reaction window to save the unit.

Sequence:

• Player A plays Disintegrate (target selected on play)
• Player B can play En Garde here
• If En Garde is played, it resolves first, boosting the unit's might
• Then Disintegrate resolves against the now-boosted unit
• Cleanup occurs immediately after Disintegrate resolves, killing any units with lethal damage
• No reaction window exists between spell resolution and unit death

Nuances:

• Targets for spells are selected on play, not on resolution (unless the spell specifically says otherwise)
• Cleanup occurs any time a Chain Item is removed from the Chain
• Example 1 (playing En Garde before Disintegrate resolves) is correct
• Example 2 (trying to play En Garde after Disintegrate resolves) is incorrect - no reaction window exists