fix(artwork): restore synthetic-artist guard and unicode normalization in agent lookups

Moving agent calls into the worker bypassed two behaviors of the aggregate provider:
Agents.GetArtistImages' guard for Unknown/Various Artists (a direct retriever call
could assign an unrelated image to a synthetic artist), and auxAlbum/auxArtist.Name's
DevPreserveUnicodeInExternalCalls normalization (records with typographic quotes/dashes
missed exact-name searches). Re-apply both before enumerating retrievers.

core/artwork/agent_images.go

@@ -6,10 +6,23 @@ import (
 	"io"
 	"net/url"
 
+	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/core/agents"
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/utils/str"
 )
 
+// externalName applies the DevPreserveUnicodeInExternalCalls normalization the aggregate
+// provider used, so agent searches match the same way (typographic quotes/dashes cleared
+// unless preserved).
+func externalName(name string) string {
+	if conf.Server.DevPreserveUnicodeInExternalCalls {
+		return name
+	}
+	return str.Clear(name)
+}
+
 // gateFunc gates one named external fetch (rate limit + circuit breaker per name).
 // resolveItem defaults to passthroughGate; the worker injects the per-agent gate.
 type gateFunc = func(name string, f func() (io.ReadCloser, string, error)) (io.ReadCloser, string, error)
@@ -49,9 +62,16 @@ func bestImageURL(imgs []agents.ExternalImage) *url.URL {
 // Returns the winning reader + agent name; extErr is true only when NO agent succeeded and
 // at least one failed transiently (a later success beats an earlier agent error).
 func fetchArtistImage(ctx context.Context, ag *agents.Agents, gate gateFunc, ar model.Artist) (r io.ReadCloser, agentName string, extErr bool) {
+	// Synthetic artists have no real external image; mirror Agents.GetArtistImages' guard so a
+	// direct retriever call can't assign an unrelated result to Unknown/Various Artists.
+	switch ar.ID {
+	case consts.UnknownArtistID, consts.VariousArtistsID:
+		return nil, "", false
+	}
+	name := externalName(ar.Name)
 	for _, a := range ag.ArtistImageAgents() {
 		reader, _, err := gate(a.Name, func() (io.ReadCloser, string, error) {
-			imgs, err := a.Retriever.GetArtistImages(ctx, ar.ID, ar.Name, ar.MbzArtistID)
+			imgs, err := a.Retriever.GetArtistImages(ctx, ar.ID, name, ar.MbzArtistID)
 			if err != nil {
 				return nil, "", err
 			}
@@ -73,9 +93,10 @@ func fetchArtistImage(ctx context.Context, ag *agents.Agents, gate gateFunc, ar
 
 // fetchAlbumImage is the album counterpart of fetchArtistImage.
 func fetchAlbumImage(ctx context.Context, ag *agents.Agents, gate gateFunc, al model.Album) (r io.ReadCloser, agentName string, extErr bool) {
+	name, artist := externalName(al.Name), externalName(al.AlbumArtist)
 	for _, a := range ag.AlbumImageAgents() {
 		reader, _, err := gate(a.Name, func() (io.ReadCloser, string, error) {
-			imgs, err := a.Retriever.GetAlbumImages(ctx, al.Name, al.AlbumArtist, al.MbzAlbumID)
+			imgs, err := a.Retriever.GetAlbumImages(ctx, name, artist, al.MbzAlbumID)
 			if err != nil {
 				return nil, "", err
 			}

core/artwork/agent_images_test.go

@@ -9,9 +9,11 @@ import (
 
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/core/agents"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/tests"
+	"github.com/navidrome/navidrome/utils/str"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -19,22 +21,26 @@ import (
 // fakeImageAgent is a built-in agent stub implementing both image retrievers; it
 // records call counts so per-agent ordering and short-circuiting can be asserted.
 type fakeImageAgent struct {
-	name        string
-	imgs        []agents.ExternalImage
-	err         error
-	artistCalls int
-	albumCalls  int
+	name          string
+	imgs          []agents.ExternalImage
+	err           error
+	artistCalls   int
+	albumCalls    int
+	gotArtistName string
+	gotAlbumName  string
 }
 
 func (f *fakeImageAgent) AgentName() string { return f.name }
 
-func (f *fakeImageAgent) GetArtistImages(context.Context, string, string, string) ([]agents.ExternalImage, error) {
+func (f *fakeImageAgent) GetArtistImages(_ context.Context, _, name, _ string) ([]agents.ExternalImage, error) {
 	f.artistCalls++
+	f.gotArtistName = name
 	return f.imgs, f.err
 }
 
-func (f *fakeImageAgent) GetAlbumImages(context.Context, string, string, string) ([]agents.ExternalImage, error) {
+func (f *fakeImageAgent) GetAlbumImages(_ context.Context, name, _, _ string) ([]agents.ExternalImage, error) {
 	f.albumCalls++
+	f.gotAlbumName = name
 	return f.imgs, f.err
 }
 
@@ -109,6 +115,28 @@ var _ = Describe("agent images", func() {
 			Expect(extErr).To(BeFalse())
 		})
 
+		It("skips the external lookup for synthetic artists", func() {
+			a := &fakeImageAgent{name: "agentA", imgs: []agents.ExternalImage{img("/a", 100)}}
+			ag := imageAgents(a)
+
+			for _, id := range []string{consts.UnknownArtistID, consts.VariousArtistsID} {
+				r, name, extErr := fetchArtistImage(ctx, ag, passthroughGate, model.Artist{ID: id, Name: "Various Artists"})
+				Expect(r).To(BeNil())
+				Expect(name).To(BeEmpty())
+				Expect(extErr).To(BeFalse())
+			}
+			Expect(a.artistCalls).To(Equal(0), "synthetic artists never reach the agents")
+		})
+
+		It("clears typographic characters from the query name unless preserving unicode", func() {
+			conf.Server.DevPreserveUnicodeInExternalCalls = false
+			a := &fakeImageAgent{name: "agentA"}
+			ag := imageAgents(a)
+
+			_, _, _ = fetchArtistImage(ctx, ag, passthroughGate, model.Artist{ID: "ar1", Name: "AC’DC"})
+			Expect(a.gotArtistName).To(Equal(str.Clear("AC’DC")))
+		})
+
 		It("falls through to a later agent, and its success beats the earlier error", func() {
 			a := &fakeImageAgent{name: "agentA", err: errBreakerOpen}
 			b := &fakeImageAgent{name: "agentB", imgs: []agents.ExternalImage{img("/b", 50)}}