verify_connection appears to be returning an empty list for users with active subscriptions

[jrconlin]

See mozilla/application-services#3314 (comment)

Verify that users, particularly mobile users, channels are being registered correctly and are returned as part of the verify_connection() call. This is impeding work and analysis on Send Tab reliability.

[rfk]

Ref mozilla/application-services#3314 (comment), I think that the server may be returning registered channels in cases where the client expects it to not, rather than not returning channels when the client expects that it should.

[jrconlin]

I'm not sure how this might happen, unless either the unsubscribe call failed for a given ChannelID and the client did not handle it properly, or if there might be some race condition where the unsubscribe was still pending and a verify was submitted.

We have a number of both unit and integration tests that check to ensure that a given channel is removed, while other channels remain in tact, during an unsubscribe. Still, chaos is ever present. I'm just not quite sure how to pursue this on the server.

[jrconlin]

De-prioritizing this bug since no work is currently required for the autopush server.

[rfk]

Based on discussion in the linked appservices issue, I believe the server is behaving as expected here.