feat(music): W22 shared listening + release 0.6.0

Personal playlist on a dedicated music player (browse/play/prev/next/
seek/volume/reorder/remove, .pls/.m3u import), plus per-person shared
listening: broadcast your track over presence, peers tune in and stream
it point-to-point over the files plane. Playback is timeline-synced
(play/pause/skip/seek mirror with no drift) with gapless prefetch of the
next track and independent per-source volume per listener.

In the 3-column layout the playlist gets its own card stacked under the
chat, with a resizable divider and its own scrollbar; other layouts keep
it in the Controls panel.

Breaking wire change: gossip protocol v5 (presence gains music fields),
so 0.6.0 peers cannot share a swarm with 0.5.x. Version bumped 0.5.1 ->
0.6.0; CHANGELOG updated.

Untrusted-input handling: broadcast track name sanitized and size
cap-checked at gossip ingest, fetched bytes confirmed audio before
decode, only the descriptor rides gossip (bytes go point-to-point, one
fetch in flight).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/config.rs

@@ -126,6 +126,10 @@ fn default_chat_height() -> f32 {
     180.0
 }
 
+fn default_threecol_playlist_height() -> f32 {
+    220.0
+}
+
 fn default_controls_width() -> f32 {
     280.0
 }
@@ -160,6 +164,16 @@ pub struct AppConfig {
     /// level shared by every uploaded clip so the slider sticks across plays.
     #[serde(default = "default_volume")]
     pub clip_volume: f32,
+    /// W22 music: the user's personal playlist as local file PATHS (not bytes).
+    /// Loaded into memory at startup; missing files are skipped/marked on play.
+    #[serde(default)]
+    pub music_playlist: Vec<String>,
+    /// W22 music: local playback gain for the dedicated music player (1.0 = unity).
+    #[serde(default = "default_volume")]
+    pub music_volume: f32,
+    /// W22 music: opt-in shared listening broadcast toggle. Local preference.
+    #[serde(default)]
+    pub music_broadcast: bool,
     /// When true, `clip_volume` governs every clip. When false, each clip keeps
     /// its own (in-memory) level and the universal slider is inactive.
     #[serde(default = "default_true")]
@@ -182,6 +196,11 @@ pub struct AppConfig {
     pub participants_width: f32,
     #[serde(default = "default_chat_height")]
     pub chat_height: f32,
+    /// Height (px) of the standalone Playlist card stacked under Chat in the
+    /// 3-column layout. Resized via its own horizontal divider; re-clamped to the
+    /// window on load/resize. Only used by `RoomLayout::ThreeColumn`.
+    #[serde(default = "default_threecol_playlist_height")]
+    pub threecol_playlist_height: f32,
     /// Controls panel width for the 3-column layout (px).
     #[serde(default = "default_controls_width")]
     pub controls_width: f32,
@@ -287,6 +306,11 @@ pub struct AppConfig {
     /// string. Local preference only; never sent to peers. Absent entry = unity.
     #[serde(default)]
     pub peer_volume: HashMap<String, f32>,
+    /// Per-source music listen volume/gain (`1.0` = unity), keyed by peer node id
+    /// string. Local preference only; never sent to peers. Absent entry falls
+    /// back to `music_volume`.
+    #[serde(default)]
+    pub music_source_volume: HashMap<String, f32>,
     /// Per-peer listener-side noise-gate threshold (normalized RMS, `0.0` = off),
     /// keyed by peer node id string. Local preference only; never sent to peers.
     /// Absent entry = gate disabled (pass-through).
@@ -321,6 +345,9 @@ impl Default for AppConfig {
             input_volume: 1.0,
             output_volume: 1.0,
             clip_volume: 1.0,
+            music_playlist: Vec::new(),
+            music_volume: 1.0,
+            music_broadcast: false,
             clip_volume_universal: true,
             network_mode: NetworkMode::default(),
             presence_mode: crate::presence::PresenceMode::default(),
@@ -328,6 +355,7 @@ impl Default for AppConfig {
             notifications_enabled: true,
             participants_width: default_participants_width(),
             chat_height: default_chat_height(),
+            threecol_playlist_height: default_threecol_playlist_height(),
             controls_width: default_controls_width(),
             chat_drawer_width: default_chat_drawer_width(),
             room_layout: RoomLayout::default(),
@@ -360,6 +388,7 @@ impl Default for AppConfig {
             peer_eq: HashMap::new(),
             peer_pan: HashMap::new(),
             peer_volume: HashMap::new(),
+            music_source_volume: HashMap::new(),
             peer_gate: HashMap::new(),
             hotkeys: crate::hotkeys::HotkeyMap::default(),
             window_width: default_window_width(),
@@ -516,6 +545,7 @@ mod tests {
         assert!(deserialized.peer_eq.is_empty());
         assert!(deserialized.peer_pan.is_empty());
         assert!(deserialized.peer_volume.is_empty());
+        assert!(deserialized.music_source_volume.is_empty());
         assert!(deserialized.peer_gate.is_empty());
         assert_eq!(
             crate::hotkeys::format_binding(
@@ -668,6 +698,9 @@ mod tests {
         assert_eq!(def.input_volume, 1.0);
         assert_eq!(def.output_volume, 1.0);
         assert_eq!(def.clip_volume, 1.0);
+        assert!(def.music_playlist.is_empty());
+        assert_eq!(def.music_volume, 1.0);
+        assert!(!def.music_broadcast);
         assert!(def.clip_volume_universal);
 
         // Missing in JSON → unity (serde default).
@@ -676,6 +709,9 @@ mod tests {
         assert_eq!(cfg_missing.input_volume, 1.0);
         assert_eq!(cfg_missing.output_volume, 1.0);
         assert_eq!(cfg_missing.clip_volume, 1.0);
+        assert!(cfg_missing.music_playlist.is_empty());
+        assert_eq!(cfg_missing.music_volume, 1.0);
+        assert!(!cfg_missing.music_broadcast);
         // Configs predating the toggle default to universal mode.
         assert!(cfg_missing.clip_volume_universal);
 
@@ -684,6 +720,9 @@ mod tests {
             input_volume: 1.5,
             output_volume: 0.25,
             clip_volume: 0.7,
+            music_playlist: vec!["/tmp/song.ogg".to_string()],
+            music_volume: 0.6,
+            music_broadcast: true,
             clip_volume_universal: false,
             ..AppConfig::default()
         };
@@ -692,6 +731,9 @@ mod tests {
         assert_eq!(round_tripped.input_volume, 1.5);
         assert_eq!(round_tripped.output_volume, 0.25);
         assert_eq!(round_tripped.clip_volume, 0.7);
+        assert_eq!(round_tripped.music_playlist, vec!["/tmp/song.ogg".to_string()]);
+        assert_eq!(round_tripped.music_volume, 0.6);
+        assert!(round_tripped.music_broadcast);
         assert!(!round_tripped.clip_volume_universal);
     }