refactor(transcoding): rename EnableTranscodingCancellation to Transcoding.EnableCancellation (#5523)

Move the option into the nested Transcoding config group alongside the
limit knobs it interacts with, so all transcoding-related settings live
together.

The old top-level name is still honored via the existing
mapDeprecatedOption / logDeprecatedOptions plumbing, which forwards the
value to the new key and logs a deprecation warning at startup. The old
struct field is removed (the new field is the single source of truth);
the deprecated default is removed so viper.IsSet correctly distinguishes
"user set the legacy option" from "no one set it."

conf/configuration.go

@@ -47,7 +47,6 @@ type configOptions struct {
 	UIWelcomeMessage                string
 	MaxSidebarPlaylists             int
 	EnableTranscodingConfig         bool
-	EnableTranscodingCancellation   bool
 	EnableDownloads                 bool
 	EnableExternalServices          bool
 	EnableM3UExternalAlbumArt       bool
@@ -169,6 +168,7 @@ type scannerOptions struct {
 type transcodingOptions struct {
 	MaxConcurrent        int
 	MaxConcurrentPerUser int
+	EnableCancellation   bool
 }
 
 type subsonicOptions struct {
@@ -330,6 +330,7 @@ func Load(noConfigDump bool) {
 	mapDeprecatedOption("HTTPSecurityHeaders.CustomFrameOptionsValue", "HTTPHeaders.FrameOptions")
 	mapDeprecatedOption("CoverJpegQuality", "CoverArtQuality")
 	mapDeprecatedOption("SimilarSongsMatchThreshold", "Matcher.FuzzyThreshold")
+	mapDeprecatedOption("EnableTranscodingCancellation", "Transcoding.EnableCancellation")
 
 	err := viper.Unmarshal(&Server, viper.DecodeHook(
 		mapstructure.ComposeDecodeHookFunc(
@@ -455,6 +456,7 @@ func Load(noConfigDump bool) {
 	logDeprecatedOptions("HTTPSecurityHeaders.CustomFrameOptionsValue", "HTTPHeaders.FrameOptions")
 	logDeprecatedOptions("CoverJpegQuality", "CoverArtQuality")
 	logDeprecatedOptions("SimilarSongsMatchThreshold", "Matcher.FuzzyThreshold")
+	logDeprecatedOptions("EnableTranscodingCancellation", "Transcoding.EnableCancellation")
 
 	// Removed options
 	logRemovedOptions("Spotify.ID", "Spotify.Secret")
@@ -743,7 +745,6 @@ func setViperDefaults() {
 	viper.SetDefault("uiwelcomemessage", "")
 	viper.SetDefault("maxsidebarplaylists", consts.DefaultMaxSidebarPlaylists)
 	viper.SetDefault("enabletranscodingconfig", false)
-	viper.SetDefault("enabletranscodingcancellation", false)
 	viper.SetDefault("transcodingcachesize", "100MB")
 	viper.SetDefault("imagecachesize", "100MB")
 	viper.SetDefault("albumplaycountmode", consts.AlbumPlayCountModeAbsolute)
@@ -830,6 +831,7 @@ func setViperDefaults() {
 	viper.SetDefault("subsonic.minimalclients", "SubMusic")
 	viper.SetDefault("transcoding.maxconcurrent", 0)
 	viper.SetDefault("transcoding.maxconcurrentperuser", 0)
+	viper.SetDefault("transcoding.enablecancellation", false)
 	viper.SetDefault("agents", "deezer,lastfm,listenbrainz")
 	viper.SetDefault("lastfm.enabled", true)
 	viper.SetDefault("lastfm.language", consts.DefaultInfoLanguage)

core/stream/media_streamer.go

@@ -248,10 +248,10 @@ func NewTranscodingCache() TranscodingCache {
 			// the DoS the limiter is meant to prevent.
 			//
 			// When the limiter is disabled, preserve the legacy behavior
-			// governed by EnableTranscodingCancellation so this PR does not
-			// change observable behavior for operators who have not opted in.
+			// governed by Transcoding.EnableCancellation so unchanged configs
+			// keep their previous observable behavior.
 			var transcodingCtx context.Context
-			if job.ms.limiter.Enabled() || conf.Server.EnableTranscodingCancellation {
+			if job.ms.limiter.Enabled() || conf.Server.Transcoding.EnableCancellation {
 				transcodingCtx = ctx
 			} else {
 				transcodingCtx = request.AddValues(context.Background(), ctx)