Cannot set session cookie max age in Kubernetes Spring Boot app
OK, it turned out that the session is being managed by Spring due to spring.session.store-type being set to redis in the integration environments. It's none in my local build, which means Tomcat manages the session instead. Sorry, I didn't mean to obfuscate that. I just didn't know what to look for. The default session cookie name for a Spring-managed session is SESSION, while for Tomcat, it's JSESSIONID, so I was at least right about that being the key to the mystery.
There don't seem to be properties for configuring the Spring session cookie, but I found this explanation about how to configure it in code: Spring Session - Custom Cookie