feat(artwork): hydrate and expose thumbHash on every entity

ItemArtworkInfo.Image() is the single projection every hydration branch goes
through, so adding the field there covers albums, artists, playlists and both
the own-art and inherited media-file branches.

core/artwork/blurhash/blurhash_bench_test.go

@@ -40,10 +40,9 @@ func BenchmarkEncodeAtInputSize(b *testing.B) {
 			})
 		}
 	}
-	x, y := blurhash.Components(size, size)
 	b.ReportAllocs()
 	for range b.N {
-		if _, err := blurhash.Encode(img, x, y); err != nil {
+		if _, err := blurhash.Encode(img); err != nil {
 			b.Fatal(err)
 		}
 	}

model/artwork.go

@@ -21,6 +21,7 @@ type ItemImage struct {
 	ImageHash   string `structs:"-" json:"imageHash,omitempty"`
 	ImageAbsent bool   `structs:"-" json:"imageAbsent,omitempty"`
 	BlurHash    string `structs:"-" json:"blurHash,omitempty"`
+	ThumbHash   string `structs:"-" json:"thumbHash,omitempty"`
 	// A blurhash carries no aspect ratio, so clients need these to shape the placeholder.
 	ImageWidth  int `structs:"-" json:"imageWidth,omitempty"`
 	ImageHeight int `structs:"-" json:"imageHeight,omitempty"`
@@ -52,11 +53,12 @@ type ItemArtwork struct {
 
 // ItemArtworkInfo is the list-hydration projection (item_artwork joined with artwork).
 type ItemArtworkInfo struct {
-	ItemID   string
-	Hash     string
-	BlurHash string
-	Width    int
-	Height   int
+	ItemID    string
+	Hash      string
+	BlurHash  string
+	ThumbHash string
+	Width     int
+	Height    int
 }
 
 // Absent reports a known-absent artwork state (resolved, no image).
@@ -68,6 +70,7 @@ func (i ItemArtworkInfo) Image() ItemImage {
 		ImageHash:   i.Hash,
 		ImageAbsent: i.Absent(),
 		BlurHash:    i.BlurHash,
+		ThumbHash:   i.ThumbHash,
 		ImageWidth:  i.Width,
 		ImageHeight: i.Height,
 	}

model/artwork_test.go

@@ -23,6 +23,23 @@ var _ = Describe("ItemImage JSON", func() {
 		Expect(out).To(HaveKeyWithValue("blurHash", "LEHV6nWB2yk8"))
 	})
 
+	It("exposes the thumbhash, and omits it when the entity has none", func() {
+		al := model.Album{ID: "al-4", Name: "Album"}
+		al.ThumbHash = "1QcSHQRn"
+
+		var out map[string]any
+		data, err := json.Marshal(al)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(json.Unmarshal(data, &out)).To(Succeed())
+		Expect(out).To(HaveKeyWithValue("thumbHash", "1QcSHQRn"))
+
+		var bare map[string]any
+		data, err = json.Marshal(model.Album{ID: "al-5", Name: "Album"})
+		Expect(err).ToNot(HaveOccurred())
+		Expect(json.Unmarshal(data, &bare)).To(Succeed())
+		Expect(bare).ToNot(HaveKey("thumbHash"))
+	})
+
 	// Without the dimensions, clients cannot know the placeholder's shape and default to a square.
 	It("exposes the image dimensions alongside the blurhash", func() {
 		al := model.Album{ID: "al-3", Name: "Album"}

persistence/artwork_hydration_test.go

@@ -289,12 +289,12 @@ var _ = Describe("Artwork hydration", func() {
 			Expect(byID["2002"].AlbumImage.ImageAbsent).To(BeTrue())
 		})
 
-		It("carries the blurhash and its dimensions alongside the hash in both the own-art and inherited branches", func() {
+		It("carries both hashes and the dimensions alongside the hash in the own-art and inherited branches", func() {
 			setCover("1001", true) // eligible, resolves its own art -> own-art-wins branch
 			DeferCleanup(func() { setCover("1001", false) })
 
-			Expect(aw.PutImage(&model.Artwork{Hash: "mfh1001blurxxxxx", Mime: "image/jpeg", BlurHash: "LTRACKblur", Width: 640, Height: 480})).To(Succeed())
-			Expect(aw.PutImage(&model.Artwork{Hash: "alh102blurxxxxxx", Mime: "image/jpeg", BlurHash: "LALBUMblur", Width: 1200, Height: 800})).To(Succeed())
+			Expect(aw.PutImage(&model.Artwork{Hash: "mfh1001blurxxxxx", Mime: "image/jpeg", BlurHash: "LTRACKblur", ThumbHash: "THtrack", Width: 640, Height: 480})).To(Succeed())
+			Expect(aw.PutImage(&model.Artwork{Hash: "alh102blurxxxxxx", Mime: "image/jpeg", BlurHash: "LALBUMblur", ThumbHash: "THalbum", Width: 1200, Height: 800})).To(Succeed())
 			putInfo("mf", "1001", "mfh1001blurxxxxx")
 			putInfo("al", "102", "alh102blurxxxxxx") // 1002's album: single-disc inheritance branch
 
@@ -302,11 +302,13 @@ var _ = Describe("Artwork hydration", func() {
 
 			Expect(byID["1001"].ImageHash).To(Equal("mfh1001blurxxxxx"))
 			Expect(byID["1001"].BlurHash).To(Equal("LTRACKblur"))
+			Expect(byID["1001"].ThumbHash).To(Equal("THtrack"))
 			Expect(byID["1001"].ImageWidth).To(Equal(640))
 			Expect(byID["1001"].ImageHeight).To(Equal(480))
 
 			Expect(byID["1002"].ImageHash).To(Equal("alh102blurxxxxxx"))
 			Expect(byID["1002"].BlurHash).To(Equal("LALBUMblur"))
+			Expect(byID["1002"].ThumbHash).To(Equal("THalbum"))
 			Expect(byID["1002"].ImageWidth).To(Equal(1200))
 			Expect(byID["1002"].ImageHeight).To(Equal(800))
 		})
@@ -739,13 +741,14 @@ var _ = Describe("Artwork hydration", func() {
 	Describe("applyItemImage", func() {
 		It("copies hash, absence, blurhash and dimensions onto the item", func() {
 			infos := map[string]model.ItemArtworkInfo{
-				"al-1": {ItemID: "al-1", Hash: "0123456789abcdef", BlurHash: "LEHV6nWB2yk8", Width: 1200, Height: 800},
+				"al-1": {ItemID: "al-1", Hash: "0123456789abcdef", BlurHash: "LEHV6nWB2yk8", ThumbHash: "1QcSHQRn", Width: 1200, Height: 800},
 			}
 			var img model.ItemImage
 			applyItemImage(infos, "al-1", &img)
 			Expect(img.ImageHash).To(Equal("0123456789abcdef"))
 			Expect(img.ImageAbsent).To(BeFalse())
 			Expect(img.BlurHash).To(Equal("LEHV6nWB2yk8"))
+			Expect(img.ThumbHash).To(Equal("1QcSHQRn"))
 			Expect(img.ImageWidth).To(Equal(1200))
 			Expect(img.ImageHeight).To(Equal(800))
 		})
@@ -756,6 +759,7 @@ var _ = Describe("Artwork hydration", func() {
 			applyItemImage(infos, "al-2", &img)
 			Expect(img.ImageAbsent).To(BeTrue())
 			Expect(img.BlurHash).To(BeEmpty())
+			Expect(img.ThumbHash).To(BeEmpty())
 		})
 
 		It("leaves an unresolved item zero-valued", func() {

persistence/artwork_repository.go

@@ -191,6 +191,7 @@ func (r *artworkRepository) GetInfoForItems(kind model.Kind, ids []string) (map[
 	res := map[string]model.ItemArtworkInfo{}
 	for chunk := range slices.Chunk(ids, artworkBatchSize) {
 		sel := Select("ia.item_id", "ia.hash", "COALESCE(a.blur_hash, '') as blur_hash",
+			"COALESCE(a.thumb_hash, '') as thumb_hash",
 			"COALESCE(a.width, 0) as width", "COALESCE(a.height, 0) as height").
 			From(itemArtworkTable + " ia").
 			LeftJoin("artwork a ON a.hash = ia.hash").