Can you react to abilities that don't have action and reaction keywords, such as Solari Chief's triggered ability or Singularity?

Ruling: Yes, once any ability is on the chain, players get a chance to react to it, regardless of whether the ability has action/reaction keywords. The speed of the ability that started the chain does not affect what reactions are possible.

Sequence:

• When you play Solari Chief, he starts a chain with himself as a permanent
• Permanents (units/gear) auto-resolve on the chain with no reaction window
• Once Solari Chief resolves and is in play, his "When you play me" triggered ability goes onto the chain (choices are made at this point)
• The player who played Solari Chief has priority first, then if they pass, the opponent can play reactions on top
• Once both players pass, the top item on the chain resolves
• Priority passes again and the process continues until the chain is empty

Nuances:

• Add abilities and permanents themselves do not give reaction windows
• Only cards with the "Spell" type are spells, so abilities like Solari Chief's cannot be countered by cards like Defy or Windwall that specifically counter spells
• The unit lands on the board immediately, but both players can react to its triggered ability before it resolves