feat(models,core): playlist revision evidence and track-ids fetch

Playlist and PlaylistWithTrackIds deserialize the API updated_at stamp
(absent on some list shapes, hence optional), and the core facade
exposes the lightweight playlist/get?extra=track_ids fetch the
membership hydrator drives.

cc

crates/qbz-core/src/core.rs

@@ -1419,6 +1419,22 @@ impl<A: FrontendAdapter + Send + Sync + 'static> QbzCore<A> {
             .map_err(CoreError::Api)
     }
 
+    /// Lightweight membership fetch: one playlist's track IDS only
+    /// (`playlist/get?extra=track_ids`). The membership hydrator's probe —
+    /// no Track objects, no pagination.
+    pub async fn get_playlist_track_ids(
+        &self,
+        playlist_id: u64,
+    ) -> Result<qbz_models::PlaylistWithTrackIds, CoreError> {
+        let client = self.client.read().await;
+        let client = client.as_ref().ok_or(CoreError::NotInitialized)?;
+
+        client
+            .get_playlist_track_ids(playlist_id)
+            .await
+            .map_err(CoreError::Api)
+    }
+
     /// Check how many of `track_ids` are already in the Qobuz playlist
     /// `playlist_id`. Mirrors Tauri's `v2_check_playlist_duplicates`
     /// (commands_v2/playlists.rs): fetch the playlist's existing track ids and

crates/qbz-library/src/playlist_membership.rs

@@ -34,10 +34,7 @@ pub enum PlaylistTrackRef {
     /// A library-projected row: a local file, or a Jellyfin/Subsonic track
     /// (their playlist storage identity is the projection). `path` is the
     /// `local_tracks.file_path` value local playlists key on.
-    Library {
-        track_id: i64,
-        path: Option<String>,
-    },
+    Library { track_id: i64, path: Option<String> },
     /// A Plex track by rating key.
     Plex { rating_key: String },
 }
@@ -467,7 +464,10 @@ mod tests {
         // The Qobuz playlist holds the library row and the Plex key (2 of 3);
         // the local playlist holds all three.
         assert_eq!(contained(&rows, ContainmentTarget::Qobuz(7)), Some(2));
-        assert_eq!(contained(&rows, ContainmentTarget::Local(lp.clone())), Some(3));
+        assert_eq!(
+            contained(&rows, ContainmentTarget::Local(lp.clone())),
+            Some(3)
+        );
         assert_eq!(rows[0].target, ContainmentTarget::Local(lp));
     }
 

crates/qbz-library/src/qobuz_playlist_snapshot.rs

@@ -215,10 +215,7 @@ pub fn current_generation(conn: &Connection) -> Result<i64> {
 /// An EMPTY list is still recorded (a user can genuinely delete every
 /// playlist), but the caller must only invoke this for a fetch that
 /// succeeded — a network failure must never masquerade as an empty library.
-pub fn record_authoritative_list(
-    conn: &Connection,
-    entries: &[AuthoritativeEntry],
-) -> Result<i64> {
+pub fn record_authoritative_list(conn: &Connection, entries: &[AuthoritativeEntry]) -> Result<i64> {
     let ts = now_ms();
     conn.execute_batch("BEGIN IMMEDIATE")?;
     let result = (|| -> Result<i64> {
@@ -620,9 +617,7 @@ pub fn track_ids(conn: &Connection, qobuz_playlist_id: u64) -> Result<Vec<u64>>
           WHERE qobuz_playlist_id = ?1 ORDER BY position",
     )?;
     let mut out = Vec::new();
-    for r in stmt.query_map(params![qobuz_playlist_id as i64], |r| {
-        r.get::<_, i64>(0)
-    })? {
+    for r in stmt.query_map(params![qobuz_playlist_id as i64], |r| r.get::<_, i64>(0))? {
         out.push(r? as u64);
     }
     Ok(out)

crates/qbz-models/src/types.rs

@@ -828,6 +828,10 @@ pub struct Playlist {
     pub image_rectangle_mini: Option<Vec<String>>,
     pub slug: Option<String>,
     pub users_count: Option<u32>,
+    /// API revision stamp (unix seconds). The membership index reads it as
+    /// change evidence when the API provides it; absent on some list shapes.
+    #[serde(default)]
+    pub updated_at: Option<i64>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
@@ -869,6 +873,9 @@ pub struct PlaylistWithTrackIds {
     pub images300: Option<Vec<String>>,
     pub slug: Option<String>,
     pub users_count: Option<u32>,
+    /// API revision stamp (unix seconds), when the response carries one.
+    #[serde(default)]
+    pub updated_at: Option<i64>,
 }
 
 /// Result of checking for duplicate tracks in a playlist