explicit info in GUI for playlist

internal/playback/playlist_readiness.go

@@ -112,13 +112,14 @@ func (c *PlaylistReadinessCoordinator) Run(ctx context.Context) error {
 				continue
 			}
 			statuses := c.statuses.SnapshotAll()
-			if IsSessionFailed(sessionSnapshot, statuses) {
+			if failure, failed := SessionFailureStatus(sessionSnapshot, statuses); failed {
 				if playlistSnapshot.Revision == emittedFailedRevision {
 					continue
 				}
 				failed := PlaylistEvent{
 					Revision: playlistSnapshot.Revision,
 					Kind:     PlaylistEventFailed,
+					Failure:  failure,
 				}
 				select {
 				case <-ctx.Done():
@@ -217,24 +218,39 @@ func IsSessionFailed(
 	session SessionSnapshot,
 	statuses PlaybackStatusSnapshot,
 ) bool {
+	_, failed := SessionFailureStatus(session, statuses)
+	return failed
+}
+
+func SessionFailureStatus(
+	session SessionSnapshot,
+	statuses PlaybackStatusSnapshot,
+) (Status, bool) {
 	if statuses.Generation != session.Generation {
-		return false
+		return Status{}, false
 	}
 
 	switch session.Plan.Topology {
 	case TopologyIndependent:
-		return (session.Plan.Video.Active && statusIsFailed(
+		if session.Plan.Video.Active && statusIsFailed(
 			statuses.Video, statuses.HasVideo, session.Generation, session.Plan.Video,
-		)) || (session.Plan.Audio.Active && statusIsFailed(
+		) {
+			return statuses.Video, true
+		}
+		if session.Plan.Audio.Active && statusIsFailed(
 			statuses.Audio, statuses.HasAudio, session.Generation, session.Plan.Audio,
-		))
+		) {
+			return statuses.Audio, true
+		}
+		return Status{}, false
 	case TopologySynchronized:
-		return statuses.HasSync &&
+		failed := statuses.HasSync &&
 			statuses.Sync.Generation == session.Generation &&
 			statuses.Sync.State == StateFailed &&
 			sameSyncSource(statuses.Sync.Pair, session.Plan.Sync)
+		return statuses.Sync, failed
 	default:
-		return false
+		return Status{}, false
 	}
 }