feat(artwork): persist a thumbhash alongside the blurhash

The artwork table is content-addressed, so this costs one row per unique image
rather than per entity. Measured on a 25k-image library: +0.6MB on a 727MB DB.

The column is added to the existing add_artwork_tables migration rather than a
new one, since #5847 has not been released and the table it extends ships in
that same PR.

db/migrations/20260722023032_add_artwork_tables.sql

@@ -6,6 +6,7 @@ CREATE TABLE artwork (
   height INTEGER NOT NULL DEFAULT 0,
   size_bytes INTEGER NOT NULL DEFAULT 0,
   blur_hash TEXT NOT NULL DEFAULT '',
+  thumb_hash TEXT NOT NULL DEFAULT '',
   created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
 

model/artwork.go

@@ -10,6 +10,7 @@ type Artwork struct {
 	Height    int       `structs:"height"`
 	SizeBytes int64     `structs:"size_bytes"`
 	BlurHash  string    `structs:"blur_hash"`
+	ThumbHash string    `structs:"thumb_hash"`
 	CreatedAt time.Time `structs:"created_at"`
 }
 

persistence/artwork_repository.go

@@ -54,7 +54,8 @@ func (r *artworkRepository) PutImage(a *model.Artwork) error {
 	}
 	// created_at=excluded.created_at: reacquiring an orphan must reset the prune grace window.
 	ins := Insert(r.tableName).SetMap(values).Suffix(`ON CONFLICT (hash) DO UPDATE SET mime=excluded.mime, width=excluded.width,
-		height=excluded.height, size_bytes=excluded.size_bytes, blur_hash=excluded.blur_hash, created_at=excluded.created_at`)
+		height=excluded.height, size_bytes=excluded.size_bytes, blur_hash=excluded.blur_hash,
+		thumb_hash=excluded.thumb_hash, created_at=excluded.created_at`)
 	_, err = r.executeSQL(ins)
 	return err
 }

persistence/artwork_repository_test.go

@@ -40,6 +40,25 @@ var _ = Describe("ArtworkRepository", func() {
 			Expect(got.CreatedAt).ToNot(BeZero())
 		})
 
+		It("round-trips the thumbhash alongside the blurhash", func() {
+			a := &model.Artwork{Hash: "both1", Mime: "image/jpeg", BlurHash: "LKO2?U%2Tw=w", ThumbHash: "1QcSHQRnh493V4dIh4eXh1h4kJUI"}
+			Expect(repo.PutImage(a)).To(Succeed())
+
+			got, err := repo.GetImage("both1")
+			Expect(err).ToNot(HaveOccurred())
+			Expect(got.BlurHash).To(Equal("LKO2?U%2Tw=w"))
+			Expect(got.ThumbHash).To(Equal("1QcSHQRnh493V4dIh4eXh1h4kJUI"))
+		})
+
+		It("overwrites the thumbhash on re-acquisition", func() {
+			Expect(repo.PutImage(&model.Artwork{Hash: "th2", Mime: "image/png", ThumbHash: "first"})).To(Succeed())
+			Expect(repo.PutImage(&model.Artwork{Hash: "th2", Mime: "image/png", ThumbHash: "second"})).To(Succeed())
+
+			got, err := repo.GetImage("th2")
+			Expect(err).ToNot(HaveOccurred())
+			Expect(got.ThumbHash).To(Equal("second"))
+		})
+
 		It("is idempotent on Put (upsert by hash)", func() {
 			a := &model.Artwork{Hash: "dup1", Mime: "image/png"}
 			Expect(repo.PutImage(a)).To(Succeed())