Background:
Having confidence in progress made on T127268 is dependent on Logstash telemetry from violations, which would currently be too spammy due to Gadgets being loaded unconditionally and violating the targets filter by default without a way for users to fix that. (T171180).
Analysis from @TheDJ shows that the way Gadgets enqueues the enabled Gadget modules could easily filter by target, but this is currently not working as intended because the `OutputPage::mTarget` member is not set by the time Gadgets queues its modules.
Further progress on the matter is blocked on moving the setTarget() call in MobileFrontend to an earlier hook. This is expected to be uncontroversial given the target state is declarative and aside from ResourceLoader (which only consumes it upon skin rendering) nothing reads from this variable.