Sometimes Yetibot completely breaks after running for several days with exception:

java.security.AccessControlException: access denied ("java.net.NetPermission" "getProxySelector")
        at java.base/java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)
        at java.base/java.security.AccessController.checkPermission(AccessController.java:895)
        at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:322)
        at java.base/java.net.ProxySelector.getDefault(ProxySelector.java:96)

Until we figure this out it might be worth baking a check into /healthz to ensure we can talk to the Slack API. There's even an api.test method we could utilize.