feat(artwork): re-queue an absent cover when its page is viewed

serveEntity now schedules a Bump recheck for an entity whose art was recorded
absent, so viewing a missing cover re-triggers resolution (e.g. after an
external source that was down during the scan comes back), matching the
request-time bump that already covers never-resolved entities.

Throttled by attempted_at against requestRecheckAge (1h) so repeatedly opening
a genuinely-absent page can't hammer external services. EnqueueBump preserves
an existing failed-state backoff via MAX(priority,...) and inserts a fresh,
immediately-eligible recheck for a settled-absent row (whose queue row was
already deleted).

core/artwork/serving.go

@@ -89,8 +89,13 @@ func (s *service) Get(ctx context.Context, artID model.ArtworkID, size int, squa
 	}
 }
 
+// requestRecheckAge throttles view-triggered rechecks of an absent entity so repeatedly opening a
+// genuinely-absent page can't hammer external services; below staleAbsentAge to catch younger absences.
+const requestRecheckAge = time.Hour
+
 // serveEntity serves an entity whose state the worker owns (album/artist/playlist/radio):
-// found row serves its hash, absent row is unavailable, missing row reads through provisionally.
+// found row serves its hash, absent row is unavailable (promoting a stale recheck on view),
+// missing row reads through provisionally.
 func (s *service) serveEntity(ctx context.Context, artID model.ArtworkID, size int, square bool) (*Image, error) {
 	ia, err := s.ds.Artwork(ctx).GetItemArtwork(artID.Kind.Prefix(), artID.ID, model.ImageTypePrimary)
 	switch {
@@ -99,6 +104,11 @@ func (s *service) serveEntity(ctx context.Context, artID model.ArtworkID, size i
 	case err != nil:
 		return nil, err
 	case ia.Hash == "":
+		// EnqueueBump preserves an existing backoff row's retry_at; for a settled absent row
+		// (no queue row) it inserts a fresh, immediately-eligible recheck.
+		if time.Since(ia.AttemptedAt) > requestRecheckAge {
+			s.enqueue(ctx, artID, model.ArtworkPriorityBump)
+		}
 		return nil, ErrUnavailable
 	default:
 		return s.serveHash(ctx, artID, ia, size, square)

core/artwork/serving_test.go

@@ -183,13 +183,29 @@ var _ = Describe("Service", func() {
 			Expect(queueRepo.Data[primaryKey("al", "al3b")].Priority).To(Equal(model.ArtworkPriorityScan))
 		})
 
-		It("returns ErrUnavailable for an absent state without enqueuing", func() {
+		It("does not re-enqueue a recently-attempted absent state", func() {
-			Expect(artRepo.PutItemArtwork(&model.ItemArtwork{ItemKind: "al", ItemID: "al4"})).To(Succeed())
+			Expect(artRepo.PutItemArtwork(&model.ItemArtwork{
+				ItemKind: "al", ItemID: "al4", AttemptedAt: time.Now(),
+			})).To(Succeed())
 
 			_, err := svc.Get(ctx, model.MustParseArtworkID("al-al4"), 0, false)
 			Expect(err).To(MatchError(ErrUnavailable))
 			Expect(queueRepo.Data).To(BeEmpty())
 		})
+
+		It("promotes a stale absent state at Bump priority on view", func() {
+			Expect(artRepo.PutItemArtwork(&model.ItemArtwork{
+				ItemKind: "al", ItemID: "al4b", AttemptedAt: time.Now().Add(-2 * requestRecheckAge),
+			})).To(Succeed())
+
+			_, err := svc.Get(ctx, model.MustParseArtworkID("al-al4b"), 0, false)
+			Expect(err).To(MatchError(ErrUnavailable))
+			Expect(queueRepo.Data[primaryKey("al", "al4b")].Priority).To(Equal(model.ArtworkPriorityBump))
+			// The absent state row is left intact; only a recheck is scheduled.
+			ia, err := artRepo.GetItemArtwork("al", "al4b", model.ImageTypePrimary)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ia.Hash).To(BeEmpty())
+		})
 	})
 
 	Describe("provisional read-through", func() {