Why does Disintegrate (even with errata) allow drawing a card if units with lethal damage aren't killed until cleanup, which happens after the spell resolves?

Ruling: Disintegrate's reflexive trigger remains active after the spell resolves and triggers if the unit dies during the cleanup immediately following the spell resolution, then puts the draw effect onto the chain.

Sequence:

• Disintegrate resolves, dealing damage to the unit
• Spell resolution completes
• Cleanup occurs, killing units with lethal damage
• Reflexive trigger activates if the unit died, putting draw effect on chain
• Draw effect resolves

Nuances:

• "Killed" is a defined game action (moving a unit to trash), not a status
• Units with lethal damage only get killed during cleanup, not immediately when damage is dealt
• Reflexive triggers can stay active even after the spell is in the trash, potentially supported by the rule that triggered abilities outside the board self-describe their context
• The exact mechanics of how reflexive triggers work across cleanup are not fully defined in current rules