refactor: delete dead code, dedupe helpers, add tests for untested packages

Dead code
  Removed, each verified to have no non-test caller: promptSearchSelection
  (77 lines, superseded by promptSearchSelectionMenu), AddPlaylistByTrackIDs,
  download.NewWithVerifySSL, qobuz.Client.GetTrackMetadata,
  tidal.Client.trackSupportsAtmos (test-only, and the comment above
  GetDownloadable already documented its removal from the live path) and its
  now-orphaned test, yandex.canonicalTrackRequestID (a no-op returning its
  trimmed input; the call site uses strings.TrimSpace directly) and the unused
  defaultEstimatedKbps constant.

Config keys that did nothing
  qobuz.download_booklets and misc.check_for_updates were declared, defaulted
  and documented in config.toml.example but read by no code. The whole
  [youtube] block went too: there is no YouTube provider. go-toml ignores
  unknown keys, verified, so existing user configs still load.

Duplicated helpers
  tidal.stringify and yandex.firstNonEmpty were byte-identical copies of
  jsonutil.StringFromAny and jsonutil.FirstNonEmpty. displayArtistNames
  existed three times, byte-identical, in internal/app, provider/yandex and
  provider/beatport; it now lives in jsonutil. The CLI's normalizeCodec
  delegates to config.NormalizeCodec so the flag and the config file are
  checked by the same rules.

Tests for packages that had none
  internal/jsonutil (0% -> 100%) and internal/netutil (0% -> 78%), the latter
  covering redactURL, which is a security control, and the zero-timeout
  contract that internal/download and the qobuz body copy depend on.
  internal/config rose to 82% with coverage of the new Validate(), the
  0600 permissions, CloneConfigData not sharing slices, and a concurrent
  UpdateTokens test that exercises the mutex under -race.

Test suite is ~85x faster
  Provider tests built clients with the default 60 requests/minute, so the
  rate limiter slept 1s per HTTP call: deezer took 31s, tidal 11s, qobuz 8s.
  Each provider test package now builds its config through a testConfigData
  helper that disables throttling. Whole suite: ~60s -> 0.7s, and 2.8s
  under -race.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/provider/yandex/client.go

@@ -36,7 +36,6 @@ const (
 	requestAttempts       = 3
 	desktopWindowsSignKey = "kzqU4XhfCaY6B6JTHODeq5"
 	legacyMP3SignSalt     = "XGRlBW9FXlekgbPrRHuSiA"
-	defaultEstimatedKbps  = 50000
 )
 
 var ErrMissingYandexToken = errors.New("missing yandex access_token")
@@ -180,7 +179,7 @@ func (c *Client) Close() error {
 }
 
 func (c *Client) getTrackMetadata(ctx context.Context, item string) (map[string]any, error) {
-	trackRef := canonicalTrackRequestID(item)
+	trackRef := strings.TrimSpace(item)
 	form := url.Values{}
 	form.Set("trackIds", trackRef)
 	form.Set("withMixData", "true")
@@ -577,7 +576,7 @@ func normalizeTrack(raw map[string]any, fallbackID string, artistSeparator strin
 	trackID := canonicalTrackRefFromRaw(raw, fallbackID)
 	albumRaw := firstAlbum(raw)
 	artistNames := artistNames(raw)
-	artistName := displayArtistNames(artistNames)
+	artistName := jsonutil.DisplayArtistNames(artistNames)
 	albumArtist := joinAlbumArtists(albumRaw, artistSeparator)
 	if albumArtist == "" {
 		albumArtist = artistName
@@ -596,7 +595,7 @@ func normalizeTrack(raw map[string]any, fallbackID string, artistSeparator strin
 		"tracks_count":          trackTotal,
 		"media_number":          discNumber,
 		"numberOfVolumes":       discTotal,
-		"release_date":          firstNonEmpty(jsonutil.StringFromAny(raw["releaseDate"]), jsonutil.StringFromAny(albumRaw["releaseDate"])),
+		"release_date":          jsonutil.FirstNonEmpty(jsonutil.StringFromAny(raw["releaseDate"]), jsonutil.StringFromAny(albumRaw["releaseDate"])),
 		"parental_warning":      isExplicit(raw),
 		"explicit":              isExplicit(raw),
 		"source_track_id":       jsonutil.StringFromAny(raw["realId"]),
@@ -684,9 +683,9 @@ func normalizePlaylist(raw map[string]any) map[string]any {
 		}
 	}
 	owner, _ := raw["owner"].(map[string]any)
-	ownerName := firstNonEmpty(jsonutil.StringFromAny(owner["name"]), jsonutil.StringFromAny(owner["login"]))
+	ownerName := jsonutil.FirstNonEmpty(jsonutil.StringFromAny(owner["name"]), jsonutil.StringFromAny(owner["login"]))
 	return map[string]any{
-		"id":           firstNonEmpty(jsonutil.StringFromAny(raw["playlistUuid"]), jsonutil.StringFromAny(raw["kind"])),
+		"id":           jsonutil.FirstNonEmpty(jsonutil.StringFromAny(raw["playlistUuid"]), jsonutil.StringFromAny(raw["kind"])),
 		"name":         jsonutil.StringFromAny(raw["title"]),
 		"title":        jsonutil.StringFromAny(raw["title"]),
 		"description":  jsonutil.StringFromAny(raw["description"]),
@@ -738,8 +737,8 @@ func normalizeArtistSearchItem(raw map[string]any) map[string]any {
 
 func normalizePlaylistSearchItem(raw map[string]any) map[string]any {
 	owner, _ := raw["owner"].(map[string]any)
-	ownerID := firstNonEmpty(jsonutil.StringFromAny(owner["uid"]), jsonutil.StringFromAny(raw["uid"]))
-	ownerName := firstNonEmpty(jsonutil.StringFromAny(owner["name"]), jsonutil.StringFromAny(owner["login"]))
+	ownerID := jsonutil.FirstNonEmpty(jsonutil.StringFromAny(owner["uid"]), jsonutil.StringFromAny(raw["uid"]))
+	ownerName := jsonutil.FirstNonEmpty(jsonutil.StringFromAny(owner["name"]), jsonutil.StringFromAny(owner["login"]))
 	return map[string]any{
 		"id":           ownerID + ":" + jsonutil.StringFromAny(raw["kind"]),
 		"title":        jsonutil.StringFromAny(raw["title"]),
@@ -783,7 +782,7 @@ func firstArtistID(raw map[string]any) string {
 }
 
 func joinArtists(raw map[string]any, artistSeparator string) string {
-	return displayArtistNames(artistNames(raw))
+	return jsonutil.DisplayArtistNames(artistNames(raw))
 }
 
 func artistNames(raw map[string]any) []string {
@@ -805,7 +804,7 @@ func joinAlbumArtists(albumRaw map[string]any, artistSeparator string) string {
 	if len(albumRaw) == 0 {
 		return ""
 	}
-	return displayArtistNames(albumArtistNames(albumRaw))
+	return jsonutil.DisplayArtistNames(albumArtistNames(albumRaw))
 }
 
 func albumArtistNames(albumRaw map[string]any) []string {
@@ -823,19 +822,6 @@ func albumArtistNames(albumRaw map[string]any) []string {
 	return parts
 }
 
-func displayArtistNames(names []string) string {
-	switch len(names) {
-	case 0:
-		return ""
-	case 1:
-		return names[0]
-	case 2:
-		return names[0] + " & " + names[1]
-	default:
-		return strings.Join(names[:len(names)-1], ", ") + " & " + names[len(names)-1]
-	}
-}
-
 func (c *Client) artistSeparator() string {
 	if c.cfg.Session.Metadata.ArtistSeparator == "" {
 		return "; "
@@ -852,19 +838,11 @@ func trackNumbers(albumRaw map[string]any) (int, int) {
 	return trackNumber, firstPositiveInt(jsonutil.IntFromAny(position["volume"]), 1)
 }
 
-func canonicalTrackRequestID(item string) string {
-	item = strings.TrimSpace(item)
-	if item == "" {
-		return item
-	}
-	return item
-}
-
 func canonicalTrackRefFromRaw(raw map[string]any, fallback string) string {
 	if strings.Contains(strings.TrimSpace(fallback), ":") {
 		return strings.TrimSpace(fallback)
 	}
-	trackID := firstNonEmpty(jsonutil.StringFromAny(raw["realId"]), jsonutil.StringFromAny(raw["id"]))
+	trackID := jsonutil.FirstNonEmpty(jsonutil.StringFromAny(raw["realId"]), jsonutil.StringFromAny(raw["id"]))
 	albumID := jsonutil.StringFromAny(firstAlbum(raw)["id"])
 	if trackID == "" {
 		trackID = strings.TrimSpace(fallback)
@@ -931,7 +909,7 @@ func imageMapFromTrack(raw map[string]any, albumRaw map[string]any) map[string]a
 }
 
 func imageMapFromURI(raw map[string]any) map[string]any {
-	uri := firstNonEmpty(jsonutil.StringFromAny(raw["ogImage"]), jsonutil.StringFromAny(raw["coverUri"]))
+	uri := jsonutil.FirstNonEmpty(jsonutil.StringFromAny(raw["ogImage"]), jsonutil.StringFromAny(raw["coverUri"]))
 	if uri == "" {
 		if cover, ok := raw["cover"].(map[string]any); ok {
 			uri = jsonutil.StringFromAny(cover["uri"])
@@ -1049,12 +1027,3 @@ func firstPositiveInt(vals ...int) int {
 	}
 	return 0
 }
-
-func firstNonEmpty(vals ...string) string {
-	for _, v := range vals {
-		if strings.TrimSpace(v) != "" {
-			return strings.TrimSpace(v)
-		}
-	}
-	return ""
-}

internal/provider/yandex/client_test.go

@@ -60,7 +60,7 @@ func TestGetDownloadableUsesModernGetFileInfo(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	d := config.DefaultConfigData()
+	d := testConfigData()
 	d.Downloads.RequestsPerMinute = 0
 	d.Yandex.AccessToken = "token"
 	c := New(&config.Config{File: d, Session: d})
@@ -132,7 +132,7 @@ func TestGetMetadataTrackUsesModernTracksEndpoint(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	d := config.DefaultConfigData()
+	d := testConfigData()
 	d.Downloads.RequestsPerMinute = 0
 	d.Yandex.AccessToken = "token"
 	c := New(&config.Config{File: d, Session: d})
@@ -167,13 +167,6 @@ func TestGetMetadataTrackUsesModernTracksEndpoint(t *testing.T) {
 	}
 }
 
-func TestDisplayArtistNamesUsesCreditPunctuation(t *testing.T) {
-	got := displayArtistNames([]string{"A", "B", "C"})
-	if got != "A, B & C" {
-		t.Fatalf("displayArtistNames() = %q", got)
-	}
-}
-
 func TestLegacyDirectURLBuildsPlayableMP3URL(t *testing.T) {
 	url, err := legacyDirectURL(&legacyDownloadInfoXML{
 		Host: "example.test",
@@ -189,3 +182,13 @@ func TestLegacyDirectURLBuildsPlayableMP3URL(t *testing.T) {
 		t.Fatalf("legacyDirectURL() = %q, want %q", url, want)
 	}
 }
+
+// testConfigData returns defaults with request throttling disabled.
+//
+// At the default 60 requests/minute the rate limiter sleeps 1s per request,
+// which accounted for most of this suite's runtime (deezer alone was 31s).
+func testConfigData() config.ConfigData {
+	d := config.DefaultConfigData()
+	d.Downloads.RequestsPerMinute = -1
+	return d
+}