PR #780 follow-ups: snapshot-based stale check + submit guard + dead code

- Stale-cache check (playlistTrackCacheIsStale) compared raw track_count to the
  filtered/cached track list, so any playlist with local or unavailable tracks
  always looked 'stale' and refetched + re-mirrored on every modal open. Now it
  compares the upstream snapshot_id (stored at cache time in the shared fetch
  choke point), and returns not-stale when no snapshot is available — explicit
  invalidation on refresh still handles real changes.
- organize_download: guard executor.submit so a refused job cleans up the batch
  instead of stranding it in 'analysis' (holding a limited analysis slot).
- Removed the dead, deprecated, unused mirrorSpotifyPlaylistTracks.

core/playlists/organize_download.py

@@ -152,12 +152,20 @@ def run_playlist_organize_download(
         except Exception as hist_err:
             logger.debug("organize download sync history: %s", hist_err)
 
-    deps.missing_download_executor.submit(
-        run_full_missing_tracks_process,
-        batch_id,
-        playlist_id,
-        tracks_json,
-    )
+    try:
+        deps.missing_download_executor.submit(
+            run_full_missing_tracks_process,
+            batch_id,
+            playlist_id,
+            tracks_json,
+        )
+    except Exception as submit_err:
+        # Don't leave the batch stranded in 'analysis' holding one of the limited
+        # analysis slots if the executor refuses the job.
+        logger.error("[Organize Download] Failed to submit batch %s: %s", batch_id, submit_err)
+        with tasks_lock:
+            download_batches.pop(batch_id, None)
+        return {'status': 'error', 'reason': f'submit failed: {submit_err}'}
     logger.info(
         "[Organize Download] Started batch %s for mirrored playlist %s (%s tracks)",
         batch_id,

webui/static/core.js

@@ -50,6 +50,7 @@ let _lastWatchlistScanStatus = null;
 let _lastMediaScanStatus = null;
 let _lastWishlistStats = null;
 let playlistTrackCache = {}; // Key: playlist_id, Value: tracks array
+let playlistTrackSnapshotCache = {}; // Key: playlist_id, Value: upstream snapshot_id at cache time
 let spotifyPlaylistsLoaded = false;
 let activeDownloadProcesses = {};
 let sequentialSyncManager = null;

webui/static/shared-helpers.js

@@ -1097,10 +1097,20 @@ function playlistTrackCacheIsStale(playlistId, playlist) {
     if (!cached) {
         return false;
     }
-    const expected = playlist?.track_count;
-    if (expected != null && Number(expected) !== cached.length) {
-        return true;
+    // Compare the upstream snapshot id (changes whenever the playlist's contents
+    // change). This avoids the false-positive from comparing raw track_count to
+    // the cached/filtered track list — playlists with local or unavailable
+    // tracks report a higher track_count than the id-bearing tracks we cache,
+    // which made every open look "stale" and refetch + re-mirror needlessly.
+    const currentSnap = playlist?.snapshot_id;
+    const cachedSnap = (typeof playlistTrackSnapshotCache !== 'undefined')
+        ? playlistTrackSnapshotCache[playlistId]
+        : undefined;
+    if (currentSnap && cachedSnap != null && cachedSnap !== '') {
+        return String(currentSnap) !== String(cachedSnap);
     }
+    // No reliable snapshot to compare (e.g. sources without snapshots) — don't
+    // force a refetch here; explicit invalidation on refresh handles real changes.
     return false;
 }
 
@@ -1144,6 +1154,7 @@ function isPlaylistDownloadProcessStale(playlistId, playlistMeta) {
 function invalidatePlaylistTrackCache(playlistId = null) {
     if (playlistId) {
         delete playlistTrackCache[playlistId];
+        if (typeof playlistTrackSnapshotCache !== 'undefined') delete playlistTrackSnapshotCache[playlistId];
         if (currentModalPlaylistId === playlistId) {
             currentPlaylistTracks = [];
         }
@@ -1151,6 +1162,7 @@ function invalidatePlaylistTrackCache(playlistId = null) {
         return;
     }
     playlistTrackCache = {};
+    if (typeof playlistTrackSnapshotCache !== 'undefined') playlistTrackSnapshotCache = {};
     currentPlaylistTracks = [];
     const ids = new Set();
     if (typeof spotifyPlaylists !== 'undefined' && Array.isArray(spotifyPlaylists)) {
@@ -1195,11 +1207,6 @@ function mirrorPlaylistTracksForSource(source, sourcePlaylistId, fullPlaylist) {
     });
 }
 
-/** @deprecated Use mirrorPlaylistTracksForSource */
-function mirrorSpotifyPlaylistTracks(playlistId, fullPlaylist) {
-    mirrorPlaylistTracksForSource('spotify', playlistId, fullPlaylist);
-}
-
 async function fetchAndCachePlaylistTracks(cacheKey, fetchUrl, mirrorSource, mirrorSourceId) {
     const response = await fetch(fetchUrl);
     const fullPlaylist = await response.json();
@@ -1207,6 +1214,9 @@ async function fetchAndCachePlaylistTracks(cacheKey, fetchUrl, mirrorSource, mir
         throw new Error(fullPlaylist.error);
     }
     playlistTrackCache[cacheKey] = fullPlaylist.tracks;
+    // Remember the upstream snapshot so staleness can compare against a stable
+    // signal instead of raw track_count vs the filtered track list.
+    playlistTrackSnapshotCache[cacheKey] = fullPlaylist.snapshot_id || '';
     mirrorPlaylistTracksForSource(mirrorSource, mirrorSourceId, fullPlaylist);
     return fullPlaylist;
 }