If I’m talking to you, who does not work at Stripe with me, and I promise a call from a named coworker, I would call them by their last name with no honorific. This is because my coworker is an ingroup when speaking to anyone outside the company in a business context (the outgroup).
If I were talking about that coworker with a member of my team, in most plausible cases the 3rd party coworker is the outgroup in that discussion, and I would refer to them as $NAME-san.
If I’m talking to you, who does not work at Stripe with me, and I promise a call from a named coworker, I would call them by their last name with no honorific. This is because my coworker is an ingroup when speaking to anyone outside the company in a business context (the outgroup).
If I were talking about that coworker with a member of my team, in most plausible cases the 3rd party coworker is the outgroup in that discussion, and I would refer to them as $NAME-san.