The worker's enqueue_due refuses to enqueue when a non-terminal job
already exists for a release. The search-now route enqueued
unconditionally, so two clicks (or a click racing the worker sweep)
could create two concurrent pipelines for the same album, both
importing and colliding on LibraryItem's @@unique([artist,album]).
Mirror the worker's guard: no-op if a job in a non-terminal state
(anything other than imported/needs_attention) already exists for the
release.
Jonathan
9f895cfc10