When an effect instructs you to 'play a card' (like Kai'sa champion ability or Promising Future), can other players react to the spell being played?

Ruling: Currently RAW (Rules As Written), spells played as part of another effect's resolution cannot be reacted to, as the entire "play a card" instruction must resolve completely before priority passes. However, this ruling is unclear and likely not the intended design, and Riot has not provided official clarification.

Sequence:

• The effect instructing you to play a card begins resolving
• The card is played following the complete "play a card" process through to resolution
• Only after the entire instruction completes can other players gain priority
• For Kai'sa champion ability specifically: the spell is played and recycled as part of her ability's resolution

Nuances:

• There is significant debate about whether "play" means only putting the card on the chain versus completing full resolution
• Kai'sa's legend ability explicitly states it cannot be reacted to, suggesting if the champion ability had the same restriction it would be stated
• The rules use "play" ambiguously for both putting spells on the chain and resolving permanents
• For Promising Future, under the RAW interpretation, the player of Promising Future would be first to resolve their played card
• This interpretation conflicts with how reactions to spells normally work in the game
• Official clarification from Riot is needed