How do triggered abilities work when they occur during chain resolution, specifically when spells are still on the chain?

Ruling: When a spell resolves and triggers abilities (like Traveling Merchant's ability), those abilities are placed on the chain as pending during the spell's resolution. After the spell finishes resolving, you finalize these abilities in the order they were placed, then normal chain priority rules apply.

Sequence:

• Spell resolves and triggers abilities
• Triggered abilities are placed on the chain as pending during resolution
• Finalize the abilities in the order they were placed (making choices like targets, destinations, paying costs)
• Controller of the last chain item gets priority
• If both players pass, the ability resolves

Nuances:

• Finalizing means making choices like where units will be played, spell targets, move destinations, and paying costs for things like deflect or optional costs like accelerate
• For the first question asked: Yes, you can keep stacking reactions one at a time on the chain if your opponent doesn't react. You get the first chance to react to your own spells, and if both players pass, the last item resolves and priority goes to the controller of the next chain item.