I think we need to revisit the 204 behavior in the summary endpoint since those responses don't go too well with the Android app. It crashes when viewing a link preview which returns 204. Not sure how to iOS app behaves but the Android app behavior is probably a showstopper for the summary switchover since we cannot control the rollout of Android app updates.
Example pages
Any page not in main namespace.
Beta cluster
https://en.wikipedia.beta.wmflabs.org/wiki/Wikipedia:Community_portal
click on the department directory link. (https://en.wikipedia.beta.wmflabs.org/wiki/Wikipedia:Department_directory).
Alternatively: Local RB install pointing to prod wikis
Make sure the RB config.yaml has entries for the summary like this:
mobileapps: host: http://appservice.wmflabs.org #http://localhost:6927 summary: protocol: https implementation: mcs host: https://appservice.wmflabs.org
Pages: https://en.wikipedia.org/wiki/Help:Contents, https://en.wikipedia.org/wiki/User:BSitzmann_(WMF)/sandbox or anything else with a link to a non-main namespace page.
Android info
dev build with commit c67d784 (but that should not matter)
Dev Settings set to Beta Cluster or local RB install.
Stack trace
org.wikipedia.dev E/AndroidRuntime: FATAL EXCEPTION: main
Process: org.wikipedia.dev, PID: 26681
java.lang.NullPointerException: Attempt to invoke interface method 'boolean org.wikipedia.dataclient.page.PageSummary.hasError()' on a null object reference
at org.wikipedia.page.linkpreview.LinkPreviewDialog$2.onResponse(LinkPreviewDialog.java:292) at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:158) at android.app.ActivityThread.main(ActivityThread.java:7224) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)