test(coverart): fix registry-wipe + stale provider signature

Two distinct pre-existing test bugs in the last failing cluster:

1. newTestEnricher() called resetRegistryForTests() itself, wiping the
   fake providers callers Register() right before calling it (its own
   doc says callers register first and reconcile() picks them up). The
   ~8 TestEnrichArtist_* failures (source stayed NULL, no thumb
   written) all stem from reconcile() seeing an empty registry. Remove
   the internal reset; make every caller that lacked one own the
   registry lifecycle explicitly (resetRegistryForTests + t.Cleanup):
   SidecarFound, NoSidecarNoMBID, AlreadySidecar_NoOp,
   DrainsNullSourceOnly.

2. apiTestAlbumProvider.FetchAlbumCover had a stale signature
   (context, string) predating the AlbumRef refactor; it no longer
   satisfied coverart.AlbumCoverProvider, so the p.(AlbumCoverProvider)
   capability assertion failed and TestAdminListCoverSources got
   supports=[]. Fix the param to coverart.AlbumRef.

Test-only. (A1/A2 were correct; they unmasked these. Any residual
album-enricher semantics failures will be root-caused from the next
clean run, not bundled speculatively.)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/api/admin_cover_sources_test.go

@@ -27,7 +27,7 @@ func (p *apiTestAlbumProvider) DisplayName() string                         { re
 func (p *apiTestAlbumProvider) RequiresAPIKey() bool                        { return false }
 func (p *apiTestAlbumProvider) DefaultEnabled() bool                        { return true }
 func (p *apiTestAlbumProvider) Configure(_ coverart.ProviderSettings) error { return nil }
-func (p *apiTestAlbumProvider) FetchAlbumCover(_ context.Context, _ string) ([]byte, error) {
+func (p *apiTestAlbumProvider) FetchAlbumCover(_ context.Context, _ coverart.AlbumRef) ([]byte, error) {
 	return []byte("img"), nil
 }
 

internal/coverart/enricher_test.go

@@ -49,8 +49,11 @@ func discardLogger() *slog.Logger {
 // pick them up.
 func newTestEnricher(t *testing.T, pool *pgxpool.Pool) *Enricher {
 	t.Helper()
-	resetRegistryForTests()
-	t.Cleanup(resetRegistryForTests)
+	// Do NOT reset the registry here: callers register their fakes
+	// before calling this (see doc above) and resetting would wipe them
+	// so reconcile() sees zero providers — every art source then stays
+	// NULL. Registry lifecycle is the caller's (each test does
+	// resetRegistryForTests + t.Cleanup before Register()).
 	s, err := NewSettingsService(context.Background(), pool, discardLogger())
 	if err != nil {
 		t.Fatalf("NewSettingsService: %v", err)
@@ -100,6 +103,8 @@ func TestEnrichAlbum_SidecarFound(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	resetRegistryForTests() // deterministic empty registry (sidecar-only path)
+	t.Cleanup(resetRegistryForTests)
 	e := newTestEnricher(t, pool)
 	if err := e.EnrichAlbum(context.Background(), id); err != nil {
 		t.Fatalf("enrich: %v", err)
@@ -119,6 +124,8 @@ func TestEnrichAlbum_SidecarFound(t *testing.T) {
 func TestEnrichAlbum_NoSidecarNoMBID_LeavesNull(t *testing.T) {
 	pool := newPool(t)
 	id, _ := seedAlbumWithTrack(t, pool, "NoMbid", "Artist", "")
+	resetRegistryForTests() // deterministic empty registry (no provider can supply)
+	t.Cleanup(resetRegistryForTests)
 	e := newTestEnricher(t, pool)
 	if err := e.EnrichAlbum(context.Background(), id); err != nil {
 		t.Fatalf("enrich: %v", err)
@@ -227,6 +234,8 @@ func TestEnrichAlbum_AlreadySidecar_NoOp(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	resetRegistryForTests() // deterministic empty registry (sidecar-only path)
+	t.Cleanup(resetRegistryForTests)
 	e := newTestEnricher(t, pool)
 	if err := e.EnrichAlbum(context.Background(), id); err != nil {
 		t.Fatalf("first enrich: %v", err)
@@ -262,6 +271,8 @@ func TestEnrichBatch_DrainsNullSourceOnly(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	resetRegistryForTests() // deterministic empty registry
+	t.Cleanup(resetRegistryForTests)
 	e := newTestEnricher(t, pool)
 	processed, _, _, err := e.EnrichBatch(context.Background(), 100, nil)
 	if err != nil {