Add file-based persistence for Spotify missing tracks cache

- Save missing tracks to /app/cache/spotify/*.json files
- 24-hour TTL for file cache
- Fallback to file cache when Redis is empty/restarted
- Controller checks file cache before returning empty playlists
- Ensures playlist data persists across Redis restarts

allstarr/Controllers/JellyfinController.cs

@@ -1962,6 +1962,20 @@ public class JellyfinController : ControllerBase
             var missingTracksKey = $"spotify:missing:{spotifyPlaylistName}";
             var missingTracks = await _cache.GetAsync<List<allstarr.Models.Spotify.MissingTrack>>(missingTracksKey);
             
+            // Fallback to file cache if Redis is empty
+            if (missingTracks == null || missingTracks.Count == 0)
+            {
+                missingTracks = await LoadMissingTracksFromFile(spotifyPlaylistName);
+                
+                // If we loaded from file, restore to Redis
+                if (missingTracks != null && missingTracks.Count > 0)
+                {
+                    await _cache.SetAsync(missingTracksKey, missingTracks, TimeSpan.FromHours(24));
+                    _logger.LogInformation("Restored {Count} missing tracks from file cache for {Playlist}", 
+                        missingTracks.Count, spotifyPlaylistName);
+                }
+            }
+            
             if (missingTracks == null || missingTracks.Count == 0)
             {
                 _logger.LogInformation("No missing tracks found for {Playlist}, returning {Count} existing tracks", 
@@ -2069,6 +2083,44 @@ public class JellyfinController : ControllerBase
         }
     }
 
+    /// <summary>
+    /// Loads missing tracks from file cache as fallback when Redis is empty.
+    /// </summary>
+    private async Task<List<allstarr.Models.Spotify.MissingTrack>?> LoadMissingTracksFromFile(string playlistName)
+    {
+        try
+        {
+            var safeName = string.Join("_", playlistName.Split(Path.GetInvalidFileNameChars()));
+            var filePath = Path.Combine("/app/cache/spotify", $"{safeName}_missing.json");
+            
+            if (!System.IO.File.Exists(filePath))
+            {
+                _logger.LogDebug("No file cache found for {Playlist} at {Path}", playlistName, filePath);
+                return null;
+            }
+            
+            var fileAge = DateTime.UtcNow - System.IO.File.GetLastWriteTimeUtc(filePath);
+            if (fileAge > TimeSpan.FromHours(24))
+            {
+                _logger.LogDebug("File cache for {Playlist} is too old ({Age:F1}h)", playlistName, fileAge.TotalHours);
+                return null;
+            }
+            
+            var json = await System.IO.File.ReadAllTextAsync(filePath);
+            var tracks = JsonSerializer.Deserialize<List<allstarr.Models.Spotify.MissingTrack>>(json);
+            
+            _logger.LogInformation("Loaded {Count} missing tracks from file cache for {Playlist} (age: {Age:F1}h)", 
+                tracks?.Count ?? 0, playlistName, fileAge.TotalHours);
+            
+            return tracks;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Failed to load missing tracks from file for {Playlist}", playlistName);
+            return null;
+        }
+    }
+
     /// <summary>
     /// Manual trigger endpoint to force fetch Spotify missing tracks.
     /// GET /spotify/sync?api_key=YOUR_KEY

allstarr/Services/Spotify/SpotifyMissingTracksFetcher.cs

@@ -17,6 +17,7 @@ public class SpotifyMissingTracksFetcher : BackgroundService
     private readonly IServiceProvider _serviceProvider;
     private bool _hasRunOnce = false;
     private Dictionary<string, string> _playlistIdToName = new();
+    private const string CacheDirectory = "/app/cache/spotify";
 
     public SpotifyMissingTracksFetcher(
         IOptions<SpotifyImportSettings> spotifySettings,
@@ -39,6 +40,9 @@ public class SpotifyMissingTracksFetcher : BackgroundService
         _logger.LogInformation("========================================");
         _logger.LogInformation("SpotifyMissingTracksFetcher: Starting up...");
         
+        // Ensure cache directory exists
+        Directory.CreateDirectory(CacheDirectory);
+        
         if (!_spotifySettings.Value.Enabled)
         {
             _logger.LogInformation("Spotify playlist injection is DISABLED");
@@ -125,9 +129,28 @@ public class SpotifyMissingTracksFetcher : BackgroundService
 
     private async Task<bool> ShouldRunOnStartupAsync()
     {
-        // Check if any playlist has cached data from the last 24 hours
+        // Check file cache first, then Redis
         foreach (var playlistName in _playlistIdToName.Values)
         {
+            var filePath = GetCacheFilePath(playlistName);
+            if (File.Exists(filePath))
+            {
+                var fileAge = DateTime.UtcNow - File.GetLastWriteTimeUtc(filePath);
+                if (fileAge < TimeSpan.FromHours(24))
+                {
+                    _logger.LogInformation("Found recent file cache for {Playlist} (age: {Age:F1}h)", 
+                        playlistName, fileAge.TotalHours);
+                    
+                    // Load from file into Redis if not already there
+                    var cacheKey = $"spotify:missing:{playlistName}";
+                    if (!await _cache.ExistsAsync(cacheKey))
+                    {
+                        await LoadFromFileCache(playlistName);
+                    }
+                    return false;
+                }
+            }
+            
             var cacheKey = $"spotify:missing:{playlistName}";
             if (await _cache.ExistsAsync(cacheKey))
             {
@@ -137,6 +160,59 @@ public class SpotifyMissingTracksFetcher : BackgroundService
         return true; // No recent data, should fetch
     }
     
+    private string GetCacheFilePath(string playlistName)
+    {
+        var safeName = string.Join("_", playlistName.Split(Path.GetInvalidFileNameChars()));
+        return Path.Combine(CacheDirectory, $"{safeName}_missing.json");
+    }
+    
+    private async Task LoadFromFileCache(string playlistName)
+    {
+        try
+        {
+            var filePath = GetCacheFilePath(playlistName);
+            if (!File.Exists(filePath))
+                return;
+            
+            var json = await File.ReadAllTextAsync(filePath);
+            var tracks = JsonSerializer.Deserialize<List<MissingTrack>>(json);
+            
+            if (tracks != null && tracks.Count > 0)
+            {
+                var cacheKey = $"spotify:missing:{playlistName}";
+                var fileAge = DateTime.UtcNow - File.GetLastWriteTimeUtc(filePath);
+                var ttl = TimeSpan.FromHours(24) - fileAge;
+                
+                if (ttl > TimeSpan.Zero)
+                {
+                    await _cache.SetAsync(cacheKey, tracks, ttl);
+                    _logger.LogInformation("Loaded {Count} tracks from file cache for {Playlist}", 
+                        tracks.Count, playlistName);
+                }
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Failed to load file cache for {Playlist}", playlistName);
+        }
+    }
+    
+    private async Task SaveToFileCache(string playlistName, List<MissingTrack> tracks)
+    {
+        try
+        {
+            var filePath = GetCacheFilePath(playlistName);
+            var json = JsonSerializer.Serialize(tracks, new JsonSerializerOptions { WriteIndented = true });
+            await File.WriteAllTextAsync(filePath, json);
+            _logger.LogInformation("Saved {Count} tracks to file cache for {Playlist}", 
+                tracks.Count, playlistName);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to save file cache for {Playlist}", playlistName);
+        }
+    }
+
     private async Task FetchMissingTracksAsync(CancellationToken cancellationToken)
     {
         var settings = _spotifySettings.Value;
@@ -262,7 +338,11 @@ public class SpotifyMissingTracksFetcher : BackgroundService
                 if (tracks.Count > 0)
                 {
                     var cacheKey = $"spotify:missing:{playlistName}";
+                    
+                    // Save to both Redis and file
                     await _cache.SetAsync(cacheKey, tracks, TimeSpan.FromHours(24));
+                    await SaveToFileCache(playlistName, tracks);
+                    
                     _logger.LogInformation(
                         "✓ Cached {Count} missing tracks for {Playlist} from {Filename}",
                         tracks.Count, playlistName, filename);