award_coins answers the new balance; json_decode gave an int and
SupabaseClient::request(), typed to return an array, threw a TypeError.
Every achievement that paid coins answered 500 after the coins were
already granted (seen in production on achievements.php). Scalars now
come back as ['result' => value]; error bodies that are not objects no
longer index into a scalar.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>