PostgreSQL trigger causing infinite recursion when updating same table - how to prevent trigger from firing recursively?

You have to avoid the endless loop. It seems like the function syncproductfrom_summary() is involved. Review your logic.

Maybe this article has some approaches that work for you?

www.cybertec-postgresql.com: Dealing with trigger recursion in PostgreSQL

1. Is there a way to detect if we're already inside a trigger execution?

pgtriggerdepth()

2. Should I use a flag or session variable to control trigger execution?

No, at least not this aspect of it.

It would help if you attached the definitions of triggers you create on all tables involved. It looks like you have triggers on both product_summary and products, which keep modifying and firing each other.

Take a look at pgaudit