make quick connect authorize atomic and stop the fallback shadowing redis

Move the pending requests and authorized secrets out of process so the
initiate, authorize and exchange legs can land on different replicas.

.woodpecker/ci.yaml

@@ -47,6 +47,7 @@ steps:
   # Its data directory lives on the step's ephemeral storage, not on the workspace volume.
   # Both projects attach to it through JELLYFIN_TEST_POSTGRES and give every test a database of
   # its own, so nothing here depends on a docker daemon.
+  # Valkey runs in the step for the same reason, attached through JELLYFIN_TEST_REDIS.
   - name: postgres-migration-chain
     image: mcr.microsoft.com/dotnet/sdk:10.0
     depends_on:
@@ -55,13 +56,16 @@ steps:
       DOTNET_CLI_TELEMETRY_OPTOUT: "1"
       DOTNET_NOLOGO: "1"
       JELLYFIN_TEST_POSTGRES: "Host=127.0.0.1;Port=5432;Database=postgres;Username=postgres"
+      JELLYFIN_TEST_REDIS: "127.0.0.1:6379"
     commands:
       - apt-get -o Acquire::Retries=3 update || apt-get -o Acquire::Retries=3 update
-      - DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends postgresql
+      - DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends postgresql valkey-server
       - install -d -o postgres -g postgres /tmp/pgdata /tmp/pgrun
       - PGBIN=$(ls -d /usr/lib/postgresql/*/bin | tail -1)
       - su postgres -c "$PGBIN/initdb -D /tmp/pgdata -A trust -U postgres"
       - su postgres -c "$PGBIN/pg_ctl -D /tmp/pgdata -o \"-c listen_addresses=127.0.0.1 -k /tmp/pgrun\" -l /tmp/pg.log -w start"
+      - valkey-server --daemonize yes --bind 127.0.0.1 --port 6379 --save ''
+      - valkey-cli ping
       - dotnet build tests/Jellyfin.Server.Tests/Jellyfin.Server.Tests.csproj -c Release
       - dotnet build tests/Jellyfin.Database.Tests.PostgreSQL/Jellyfin.Database.Tests.PostgreSQL.csproj -c Release
       - dotnet test tests/Jellyfin.Server.Tests/Jellyfin.Server.Tests.csproj -c Release --no-build --verbosity minimal --filter "Category=RequiresDocker"

Emby.Server.Implementations/AppBase/BaseConfigurationManager.cs

@@ -87,6 +87,12 @@ namespace Emby.Server.Implementations.AppBase
         /// <value>The application paths.</value>
         public IApplicationPaths CommonApplicationPaths { get; private set; }
 
+        /// <summary>
+        /// Gets or sets the bus announcing configuration writes to the other instances sharing this
+        /// configuration directory. Defaults to a no-op, which is the single-instance behaviour.
+        /// </summary>
+        public IConfigurationInvalidationBus InvalidationBus { get; set; } = NullConfigurationInvalidationBus.Instance;
+
         /// <summary>
         /// Gets or sets the system configuration.
         /// </summary>
@@ -169,6 +175,8 @@ namespace Emby.Server.Implementations.AppBase
             }
 
             OnConfigurationUpdated();
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.SystemConfiguration, null);
         }
 
         /// <summary>
@@ -350,6 +358,29 @@ namespace Emby.Server.Implementations.AppBase
             }
 
             OnNamedConfigurationUpdated(key, configuration);
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.NamedConfiguration, key);
+        }
+
+        /// <inheritdoc />
+        public void InvalidateCachedConfiguration(string? key)
+        {
+            if (string.IsNullOrEmpty(key))
+            {
+                lock (_configurationSyncLock)
+                {
+                    _configuration = null;
+                }
+
+                // Reloads the system configuration off the shared file as a side effect of re-deriving
+                // the cache path from it, then tells the in-process consumers to re-read it.
+                OnConfigurationUpdated();
+                return;
+            }
+
+            _configurations.TryRemove(key, out _);
+
+            OnNamedConfigurationUpdated(key, GetConfiguration(key));
         }
 
         /// <summary>

Emby.Server.Implementations/ApplicationHost.cs

@@ -706,6 +706,8 @@ namespace Emby.Server.Implementations
             BaseItem.UserDataManager = Resolve<IUserDataManager>();
             CollectionFolder.XmlSerializer = _xmlSerializer;
             CollectionFolder.ApplicationHost = this;
+            CollectionFolder.InvalidationBus = Resolve<IConfigurationInvalidationBus>();
+            ConfigurationManager.InvalidationBus = CollectionFolder.InvalidationBus;
             Folder.UserViewManager = Resolve<IUserViewManager>();
             Folder.CollectionManager = Resolve<ICollectionManager>();
             Folder.LimitedConcurrencyLibraryScheduler = Resolve<ILimitedConcurrencyLibraryScheduler>();
@@ -790,6 +792,43 @@ namespace Emby.Server.Implementations
             }
         }
 
+        /// <summary>
+        /// Works out what a configuration update means for the ports this process bound at startup.
+        /// </summary>
+        /// <param name="boundHttpPort">The HTTP port this process is bound to.</param>
+        /// <param name="boundHttpsPort">The HTTPS port this process is bound to.</param>
+        /// <param name="configuredHttpPort">The HTTP port the shared configuration now carries.</param>
+        /// <param name="configuredHttpsPort">The HTTPS port the shared configuration now carries.</param>
+        /// <param name="isPortAuthorized">Whether the shared configuration still marks the port as authorized.</param>
+        /// <param name="isApplyingRemoteInvalidation">Whether this update is another instance's write being applied.</param>
+        /// <returns>What the update requires of this instance.</returns>
+        internal static PortChangeOutcome EvaluatePortChange(
+            int boundHttpPort,
+            int boundHttpsPort,
+            int configuredHttpPort,
+            int configuredHttpsPort,
+            bool isPortAuthorized,
+            bool isApplyingRemoteInvalidation)
+        {
+            // Nothing is bound yet, so nothing has gone stale.
+            if (boundHttpPort == 0 || boundHttpsPort == 0)
+            {
+                return default;
+            }
+
+            if (configuredHttpPort == boundHttpPort && configuredHttpsPort == boundHttpsPort)
+            {
+                return default;
+            }
+
+            // Whoever wrote the change, this process is still listening on a port the configuration no
+            // longer names, so the pending restart is reported either way. The authorization flag belongs
+            // to the instance that made the change: it cleared the flag along with the port, and clearing
+            // it again here would write shared configuration on that instance's behalf and announce it a
+            // second time.
+            return new PortChangeOutcome(true, isPortAuthorized && !isApplyingRemoteInvalidation);
+        }
+
         /// <summary>
         /// Called when [configuration updated].
         /// </summary>
@@ -797,26 +836,24 @@ namespace Emby.Server.Implementations
         /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
         private void OnConfigurationUpdated(object sender, EventArgs e)
         {
-            var requiresRestart = false;
             var networkConfiguration = ConfigurationManager.GetNetworkConfiguration();
 
-            // Don't do anything if these haven't been set yet
-            if (HttpPort != 0 && HttpsPort != 0)
-            {
-                // Need to restart if ports have changed
-                if (networkConfiguration.InternalHttpPort != HttpPort
-                    || networkConfiguration.InternalHttpsPort != HttpsPort)
-                {
-                    if (ConfigurationManager.Configuration.IsPortAuthorized)
-                    {
-                        ConfigurationManager.Configuration.IsPortAuthorized = false;
-                        ConfigurationManager.SaveConfiguration();
+            var portChange = EvaluatePortChange(
+                HttpPort,
+                HttpsPort,
+                networkConfiguration.InternalHttpPort,
+                networkConfiguration.InternalHttpsPort,
+                ConfigurationManager.Configuration.IsPortAuthorized,
+                ConfigurationInvalidationContext.IsApplyingRemoteInvalidation);
 
-                        requiresRestart = true;
-                    }
-                }
+            if (portChange.ClearsPortAuthorization)
+            {
+                ConfigurationManager.Configuration.IsPortAuthorized = false;
+                ConfigurationManager.SaveConfiguration();
             }
 
+            var requiresRestart = portChange.RequiresRestart;
+
             if (ValidateSslCertificate(networkConfiguration))
             {
                 requiresRestart = true;

Emby.Server.Implementations/Configuration/ConfigurationInvalidationSubscriber.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.Entities;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Emby.Server.Implementations.Configuration
+{
+    /// <summary>
+    /// Applies the configuration invalidations published by the other instances sharing this
+    /// configuration directory, dropping the local cache entry so the next read comes off the shared file.
+    /// </summary>
+    public sealed class ConfigurationInvalidationSubscriber : IHostedService
+    {
+        private readonly IConfigurationInvalidationBus _bus;
+        private readonly IConfigurationManager _configurationManager;
+        private readonly ILogger<ConfigurationInvalidationSubscriber> _logger;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ConfigurationInvalidationSubscriber"/> class.
+        /// </summary>
+        /// <param name="bus">The invalidation bus.</param>
+        /// <param name="configurationManager">The configuration manager holding the cached configuration.</param>
+        /// <param name="logger">The logger.</param>
+        public ConfigurationInvalidationSubscriber(
+            IConfigurationInvalidationBus bus,
+            IConfigurationManager configurationManager,
+            ILogger<ConfigurationInvalidationSubscriber> logger)
+        {
+            _bus = bus;
+            _configurationManager = configurationManager;
+            _logger = logger;
+        }
+
+        /// <inheritdoc />
+        public Task StartAsync(CancellationToken cancellationToken)
+        {
+            _bus.Subscribe(Apply);
+            return Task.CompletedTask;
+        }
+
+        /// <inheritdoc />
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+        private void Apply(ConfigurationInvalidation invalidation)
+        {
+            try
+            {
+                // Applying re-raises the same update events a local save raises, so the in-process
+                // consumers re-read. The scope tells those consumers that the write was somebody else's,
+                // so the ones that answer an update by writing neither repeat it nor publish it back.
+                using var scope = ConfigurationInvalidationContext.BeginApply();
+
+                switch (invalidation.Scope)
+                {
+                    case ConfigurationInvalidationScope.SystemConfiguration:
+                        _configurationManager.InvalidateCachedConfiguration(null);
+                        break;
+                    case ConfigurationInvalidationScope.NamedConfiguration when !string.IsNullOrEmpty(invalidation.Target):
+                        _configurationManager.InvalidateCachedConfiguration(invalidation.Target);
+                        break;
+                    case ConfigurationInvalidationScope.LibraryOptions when !string.IsNullOrEmpty(invalidation.Target):
+                        CollectionFolder.InvalidateLibraryOptions(invalidation.Target);
+                        break;
+                    case ConfigurationInvalidationScope.AllLibraryOptions:
+                        CollectionFolder.InvalidateAllLibraryOptions();
+                        break;
+                    default:
+                        return;
+                }
+
+                _logger.LogDebug("Applied {Scope} invalidation for {Target} from {OriginId}.", invalidation.Scope, invalidation.Target, invalidation.OriginId);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to apply a {Scope} invalidation for {Target}.", invalidation.Scope, invalidation.Target);
+            }
+        }
+    }
+}

Emby.Server.Implementations/Configuration/RedisConfigurationInvalidationBus.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Text.Json;
+using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Configuration;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Emby.Server.Implementations.Configuration
+{
+    /// <summary>
+    /// A Redis pub/sub <see cref="IConfigurationInvalidationBus"/>. Notices are broadcast on one channel
+    /// and every instance but the publisher applies them.
+    /// </summary>
+    public sealed class RedisConfigurationInvalidationBus : IConfigurationInvalidationBus
+    {
+        private const string ChannelName = "jellyfin:configinvalidation";
+
+        private static readonly JsonSerializerOptions _jsonOptions = JsonDefaults.Options;
+
+        private readonly ISubscriber _subscriber;
+        private readonly ILogger<RedisConfigurationInvalidationBus> _logger;
+        private readonly string _originId;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RedisConfigurationInvalidationBus"/> class.
+        /// </summary>
+        /// <param name="redis">The Redis connection multiplexer.</param>
+        /// <param name="logger">The logger.</param>
+        public RedisConfigurationInvalidationBus(IConnectionMultiplexer redis, ILogger<RedisConfigurationInvalidationBus> logger)
+        {
+            ArgumentNullException.ThrowIfNull(redis);
+
+            _subscriber = redis.GetSubscriber();
+            _logger = logger;
+            _originId = Environment.GetEnvironmentVariable("JELLYFIN_INSTANCE_ID") ?? Environment.MachineName;
+        }
+
+        /// <inheritdoc />
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+        {
+            var invalidation = new ConfigurationInvalidation
+            {
+                Scope = scope,
+                Target = target,
+                OriginId = _originId
+            };
+
+            try
+            {
+                // Fire and forget: an admin saving configuration must never wait on, or fail because of,
+                // the bus. The write has already reached the shared directory by this point.
+                _subscriber.Publish(
+                    RedisChannel.Literal(ChannelName),
+                    JsonSerializer.Serialize(invalidation, _jsonOptions),
+                    CommandFlags.FireAndForget);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to publish {Scope} invalidation for {Target}; other instances keep their cached copy until they restart.", scope, target);
+            }
+        }
+
+        /// <inheritdoc />
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+        {
+            ArgumentNullException.ThrowIfNull(handler);
+
+            try
+            {
+                _subscriber.Subscribe(RedisChannel.Literal(ChannelName), (_, value) => Dispatch(handler, value));
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to subscribe to configuration invalidations; this instance keeps its cached configuration until it restarts.");
+            }
+        }
+
+        private void Dispatch(Action<ConfigurationInvalidation> handler, RedisValue value)
+        {
+            try
+            {
+                var invalidation = JsonSerializer.Deserialize<ConfigurationInvalidation>(value.ToString(), _jsonOptions);
+                if (invalidation is null || string.Equals(invalidation.OriginId, _originId, StringComparison.Ordinal))
+                {
+                    return;
+                }
+
+                handler(invalidation);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to apply a configuration invalidation.");
+            }
+        }
+    }
+}

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -2332,7 +2332,10 @@ namespace Emby.Server.Implementations.Library
         {
             IOrderedEnumerable<BaseItem>? orderedItems = null;
 
-            foreach (var orderBy in sortBy.Select(o => GetComparer(o, user)).Where(c => c is not null))
+            var comparers = sortBy.Select(o => GetComparer(o, user)).Where(c => c is not null).ToList();
+            items = PrefetchUserData(items, user, comparers);
+
+            foreach (var orderBy in comparers)
             {
                 if (orderBy is RandomComparer)
                 {
@@ -2364,14 +2367,14 @@ namespace Emby.Server.Implementations.Library
         {
             IOrderedEnumerable<BaseItem>? orderedItems = null;
 
-            foreach (var (name, sortOrder) in orderBy)
-            {
-                var comparer = GetComparer(name, user);
-                if (comparer is null)
-                {
-                    continue;
-                }
+            var comparers = orderBy
+                .Select(o => (Comparer: GetComparer(o.OrderBy, user), o.SortOrder))
+                .Where(c => c.Comparer is not null)
+                .ToList();
+            items = PrefetchUserData(items, user, comparers.Select(c => c.Comparer).ToList());
 
+            foreach (var (comparer, sortOrder) in comparers)
+            {
                 if (comparer is RandomComparer)
                 {
                     var randomItems = items.ToArray();
@@ -2397,6 +2400,31 @@ namespace Emby.Server.Implementations.Library
             return orderedItems ?? items;
         }
 
+        // The user comparers read user data per item, so without one batched read up front an
+        // in-memory sort would issue a database round trip per comparison.
+        private IEnumerable<BaseItem> PrefetchUserData(IEnumerable<BaseItem> items, User? user, IReadOnlyList<IBaseItemComparer?> comparers)
+        {
+            if (user is null)
+            {
+                return items;
+            }
+
+            var userComparers = comparers.OfType<IUserBaseItemComparer>().ToList();
+            if (userComparers.Count == 0)
+            {
+                return items;
+            }
+
+            var itemList = items as IReadOnlyList<BaseItem> ?? items.ToList();
+            var userData = _userDataManager.GetUserDataBatch(itemList, user);
+            foreach (var comparer in userComparers)
+            {
+                comparer.PrefetchedUserData = userData;
+            }
+
+            return itemList;
+        }
+
         /// <summary>
         /// Gets the comparer.
         /// </summary>

Emby.Server.Implementations/Library/UserDataManager.cs

@@ -2,10 +2,8 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Linq;
 using System.Threading;
-using BitFaster.Caching.Lru;
 using Jellyfin.Database.Implementations;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Configuration;
@@ -27,7 +25,6 @@ namespace Emby.Server.Implementations.Library
     {
         private readonly IServerConfigurationManager _config;
         private readonly IDbContextFactory<JellyfinDbContext> _repository;
-        private readonly FastConcurrentLru<string, UserItemData> _cache;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="UserDataManager"/> class.
@@ -40,7 +37,6 @@ namespace Emby.Server.Implementations.Library
         {
             _config = config;
             _repository = repository;
-            _cache = new FastConcurrentLru<string, UserItemData>(Environment.ProcessorCount, _config.Configuration.CacheSize, StringComparer.OrdinalIgnoreCase);
         }
 
         /// <inheritdoc />
@@ -77,11 +73,6 @@ namespace Emby.Server.Implementations.Library
             dbContext.SaveChanges();
             transaction.Commit();
 
-            var userId = user.InternalId;
-            var cacheKey = GetCacheKey(userId, item.Id);
-            _cache.AddOrUpdate(cacheKey, userData);
-            item.UserData = dbContext.UserData.Where(e => e.ItemId == item.Id).AsNoTracking().ToArray(); // rehydrate the cached userdata
-
             UserDataSaved?.Invoke(this, new UserDataSaveEventArgs
             {
                 Keys = keys,
@@ -180,64 +171,41 @@ namespace Emby.Server.Implementations.Library
         /// <inheritdoc />
         public Dictionary<Guid, UserItemData> GetUserDataBatch(IReadOnlyList<BaseItem> items, User user)
         {
+            ArgumentNullException.ThrowIfNull(items);
+            ArgumentNullException.ThrowIfNull(user);
+
             var result = new Dictionary<Guid, UserItemData>(items.Count);
-            var itemsNeedingQuery = new List<(BaseItem Item, List<string> Keys)>();
-
-            foreach (var item in items)
-            {
-                var cacheKey = GetCacheKey(user.InternalId, item.Id);
-                if (_cache.TryGet(cacheKey, out var cachedData))
-                {
-                    result[item.Id] = cachedData;
-                }
-                else
-                {
-                    var userDataRow = ResolveUserDataRow(item, item.UserData?.Where(e => e.UserId.Equals(user.Id)));
-                    var userData = userDataRow is not null ? Map(userDataRow) : null;
-                    if (userData is not null)
-                    {
-                        result[item.Id] = userData;
-                        _cache.AddOrUpdate(cacheKey, userData);
-                    }
-                    else
-                    {
-                        var keys = item.GetUserDataKeys();
-                        itemsNeedingQuery.Add((item, keys));
-                    }
-                }
-            }
-
-            if (itemsNeedingQuery.Count == 0)
+            if (items.Count == 0)
             {
                 return result;
             }
 
-            // Build a single query for all missing items. Fetch rows by item alone so rows kept
-            // under keys from older metadata resolve the same way as the in-memory path.
-            var allItemIds = itemsNeedingQuery.Select(x => x.Item.Id).ToList();
+            // Fetch rows by item alone so rows kept under keys from older metadata resolve the same
+            // way as the single item path.
+            var itemIds = items.Select(e => e.Id).Distinct().ToList();
             using var context = _repository.CreateDbContext();
-            var userDataArray = context.UserData
+            var userDataByItem = context.UserData
                 .AsNoTracking()
                 .Where(e => e.UserId.Equals(user.Id))
-                .WhereOneOrMany(allItemIds, e => e.ItemId)
-                .ToArray();
+                .WhereOneOrMany(itemIds, e => e.ItemId)
+                .ToArray()
+                .GroupBy(e => e.ItemId)
+                .ToDictionary(g => g.Key, g => g.ToArray());
 
-            var userDataByItem = userDataArray.GroupBy(e => e.ItemId).ToDictionary(g => g.Key, g => g.ToArray());
-            foreach (var (item, keys) in itemsNeedingQuery)
+            foreach (var item in items)
             {
-                UserItemData userData;
-                if (userDataByItem.TryGetValue(item.Id, out var itemUserData) && itemUserData.Length > 0)
+                if (result.ContainsKey(item.Id))
                 {
-                    userData = Map(ResolveUserDataRow(item, itemUserData)!);
-                }
-                else
-                {
-                    userData = new UserItemData { Key = keys.Count > 0 ? keys[0] : string.Empty };
+                    continue;
                 }
 
-                result[item.Id] = userData;
-                var cacheKey = GetCacheKey(user.InternalId, item.Id);
-                _cache.AddOrUpdate(cacheKey, userData);
+                var row = userDataByItem.TryGetValue(item.Id, out var itemUserData)
+                    ? ResolveUserDataRow(item, itemUserData)
+                    : null;
+
+                result[item.Id] = row is not null
+                    ? Map(row)
+                    : new UserItemData { Key = item.GetUserDataKeys().FirstOrDefault() ?? string.Empty };
             }
 
             return result;
@@ -340,20 +308,19 @@ namespace Emby.Server.Implementations.Library
             return result;
         }
 
-        /// <summary>
-        /// Gets the internal key.
-        /// </summary>
-        /// <returns>System.String.</returns>
-        private static string GetCacheKey(long internalUserId, Guid itemId)
-        {
-            return internalUserId.ToString(CultureInfo.InvariantCulture) + "-" + itemId.ToString("N", CultureInfo.InvariantCulture);
-        }
-
         /// <inheritdoc />
         public UserItemData? GetUserData(User user, BaseItem item)
         {
             ArgumentNullException.ThrowIfNull(user);
-            var row = ResolveUserDataRow(item, item.UserData?.Where(e => e.UserId.Equals(user.Id)));
+            ArgumentNullException.ThrowIfNull(item);
+
+            using var dbContext = _repository.CreateDbContext();
+            var rows = dbContext.UserData
+                .AsNoTracking()
+                .Where(e => e.ItemId == item.Id && e.UserId == user.Id)
+                .ToArray();
+
+            var row = ResolveUserDataRow(item, rows);
             return row is not null ? Map(row) : new UserItemData()
             {
                 Key = item.GetUserDataKeys()[0],
@@ -536,16 +503,6 @@ namespace Emby.Server.Implementations.Library
             }
 
             dbContext.SaveChanges();
-
-            var cacheKey = GetCacheKey(user.InternalId, item.Id);
-            if (_cache.TryGet(cacheKey, out var cached))
-            {
-                cached.AudioStreamIndex = null;
-                cached.SubtitleStreamIndex = null;
-                _cache.AddOrUpdate(cacheKey, cached);
-            }
-
-            item.UserData = dbContext.UserData.Where(e => e.ItemId == item.Id).AsNoTracking().ToArray();
         }
     }
 }

Emby.Server.Implementations/PortChangeOutcome.cs

@@ -0,0 +1,14 @@
+namespace Emby.Server.Implementations
+{
+    /// <summary>
+    /// What a configuration update carrying different ports requires of the instance reading it.
+    /// </summary>
+    /// <param name="RequiresRestart">
+    /// Whether this process is still bound to a port the shared configuration no longer names, and so has
+    /// to report a pending restart.
+    /// </param>
+    /// <param name="ClearsPortAuthorization">
+    /// Whether this instance is the one that has to clear the port authorization flag and save it.
+    /// </param>
+    internal readonly record struct PortChangeOutcome(bool RequiresRestart, bool ClearsPortAuthorization);
+}

Emby.Server.Implementations/QuickConnect/QuickConnectManager.cs

@@ -1,7 +1,5 @@
 using System;
-using System.Collections.Concurrent;
 using System.Globalization;
-using System.Linq;
 using System.Security.Cryptography;
 using System.Threading.Tasks;
 using MediaBrowser.Common.Extensions;
@@ -30,12 +28,10 @@ namespace Emby.Server.Implementations.QuickConnect
         /// </summary>
         private const int Timeout = 10;
 
-        private readonly ConcurrentDictionary<string, QuickConnectResult> _currentRequests = new();
-        private readonly ConcurrentDictionary<string, (DateTime Timestamp, AuthenticationResult AuthenticationResult)> _authorizedSecrets = new();
-
         private readonly IServerConfigurationManager _config;
         private readonly ILogger<QuickConnectManager> _logger;
         private readonly ISessionManager _sessionManager;
+        private readonly IQuickConnectStore _store;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="QuickConnectManager"/> class.
@@ -44,14 +40,17 @@ namespace Emby.Server.Implementations.QuickConnect
         /// <param name="config">Configuration.</param>
         /// <param name="logger">Logger.</param>
         /// <param name="sessionManager">Session Manager.</param>
+        /// <param name="store">Quick connect store.</param>
         public QuickConnectManager(
             IServerConfigurationManager config,
             ILogger<QuickConnectManager> logger,
-            ISessionManager sessionManager)
+            ISessionManager sessionManager,
+            IQuickConnectStore store)
         {
             _config = config;
             _logger = logger;
             _sessionManager = sessionManager;
+            _store = store;
         }
 
         /// <inheritdoc />
@@ -69,7 +68,7 @@ namespace Emby.Server.Implementations.QuickConnect
         }
 
         /// <inheritdoc/>
-        public QuickConnectResult TryConnect(AuthorizationInfo authorizationInfo)
+        public async Task<QuickConnectResult> TryConnect(AuthorizationInfo authorizationInfo)
         {
             ArgumentException.ThrowIfNullOrEmpty(authorizationInfo.DeviceId);
             ArgumentException.ThrowIfNullOrEmpty(authorizationInfo.Device);
@@ -77,7 +76,6 @@ namespace Emby.Server.Implementations.QuickConnect
             ArgumentException.ThrowIfNullOrEmpty(authorizationInfo.Version);
 
             AssertActive();
-            ExpireRequests();
 
             var secret = GenerateSecureRandom();
             var code = GenerateCode();
@@ -90,19 +88,17 @@ namespace Emby.Server.Implementations.QuickConnect
                 authorizationInfo.Client,
                 authorizationInfo.Version);
 
-            _currentRequests[code] = result;
+            await _store.SetRequestAsync(result, ExpiryOf(result)).ConfigureAwait(false);
             return result;
         }
 
         /// <inheritdoc/>
-        public QuickConnectResult CheckRequestStatus(string secret)
+        public async Task<QuickConnectResult> CheckRequestStatus(string secret)
         {
             AssertActive();
-            ExpireRequests();
 
-            string code = _currentRequests.Where(x => x.Value.Secret == secret).Select(x => x.Value.Code).DefaultIfEmpty(string.Empty).First();
-
-            if (!_currentRequests.TryGetValue(code, out QuickConnectResult? result))
+            var result = await _store.GetRequestBySecretAsync(secret).ConfigureAwait(false);
+            if (result is null)
             {
                 throw new ResourceNotFoundException("Unable to find request with provided secret");
             }
@@ -136,9 +132,9 @@ namespace Emby.Server.Implementations.QuickConnect
         public async Task<bool> AuthorizeRequest(Guid userId, string code)
         {
             AssertActive();
-            ExpireRequests();
 
-            if (!_currentRequests.TryGetValue(code, out QuickConnectResult? result))
+            var result = await _store.GetRequestByCodeAsync(code).ConfigureAwait(false);
+            if (result is null)
             {
                 throw new ResourceNotFoundException("Unable to find request");
             }
@@ -151,6 +147,12 @@ namespace Emby.Server.Implementations.QuickConnect
             // Change the time on the request so it expires one minute into the future. It can't expire immediately as otherwise some clients wouldn't ever see that they have been authenticated.
             result.DateAdded = DateTime.UtcNow.Add(TimeSpan.FromMinutes(1));
 
+            // The guard above is a read on shared state, so it cannot settle a race between instances; the claim can.
+            if (!await _store.TryClaimAuthorizationAsync(result.Secret, ExpiryOf(result)).ConfigureAwait(false))
+            {
+                throw new InvalidOperationException("Request is already authorized");
+            }
+
             var authenticationResult = await _sessionManager.AuthenticateDirect(new AuthenticationRequest
             {
                 UserId = userId,
@@ -160,9 +162,10 @@ namespace Emby.Server.Implementations.QuickConnect
                 AppVersion = result.AppVersion
             }).ConfigureAwait(false);
 
-            _authorizedSecrets[result.Secret] = (DateTime.UtcNow, authenticationResult);
             result.Authenticated = true;
-            _currentRequests[code] = result;
+
+            await _store.SetAuthorizationAsync(result.Secret, authenticationResult, DateTime.UtcNow.AddMinutes(Timeout)).ConfigureAwait(false);
+            await _store.SetRequestAsync(result, ExpiryOf(result)).ConfigureAwait(false);
 
             _logger.LogDebug("Authorizing device with code {Code} to login as user {UserId}", code, userId);
 
@@ -170,19 +173,21 @@ namespace Emby.Server.Implementations.QuickConnect
         }
 
         /// <inheritdoc/>
-        public AuthenticationResult GetAuthorizedRequest(string secret)
+        public async Task<AuthenticationResult> GetAuthorizedRequest(string secret)
         {
             AssertActive();
-            ExpireRequests();
 
-            if (!_authorizedSecrets.TryGetValue(secret, out var result))
+            var result = await _store.TryConsumeAuthorizationAsync(secret).ConfigureAwait(false);
+            if (result is null)
             {
                 throw new ResourceNotFoundException("Unable to find request");
             }
 
-            return result.AuthenticationResult;
+            return result;
         }
 
+        private static DateTime ExpiryOf(QuickConnectResult request) => request.DateAdded.AddMinutes(Timeout);
+
         private string GenerateSecureRandom(int length = 32)
         {
             Span<byte> bytes = stackalloc byte[length];
@@ -190,42 +195,5 @@ namespace Emby.Server.Implementations.QuickConnect
 
             return Convert.ToHexString(bytes);
         }
-
-        /// <summary>
-        /// Expire quick connect requests that are over the time limit. If <paramref name="expireAll"/> is true, all requests are unconditionally expired.
-        /// </summary>
-        /// <param name="expireAll">If true, all requests will be expired.</param>
-        private void ExpireRequests(bool expireAll = false)
-        {
-            // All requests before this timestamp have expired
-            var minTime = DateTime.UtcNow.AddMinutes(-Timeout);
-
-            // Expire stale connection requests
-            foreach (var (_, currentRequest) in _currentRequests)
-            {
-                if (expireAll || currentRequest.DateAdded < minTime)
-                {
-                    var code = currentRequest.Code;
-                    _logger.LogDebug("Removing expired request {Code}", code);
-
-                    if (!_currentRequests.TryRemove(code, out _))
-                    {
-                        _logger.LogWarning("Request {Code} already expired", code);
-                    }
-                }
-            }
-
-            foreach (var (secret, (timestamp, _)) in _authorizedSecrets)
-            {
-                if (expireAll || timestamp < minTime)
-                {
-                    _logger.LogDebug("Removing expired secret {Secret}", secret);
-                    if (!_authorizedSecrets.TryRemove(secret, out _))
-                    {
-                        _logger.LogWarning("Secret {Secret} already expired", secret);
-                    }
-                }
-            }
-        }
     }
 }

Emby.Server.Implementations/QuickConnect/RedisQuickConnectStore.cs

@@ -0,0 +1,175 @@
+using System;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using Jellyfin.Extensions.Json;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Controller.QuickConnect;
+using MediaBrowser.Model.QuickConnect;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Emby.Server.Implementations.QuickConnect;
+
+/// <summary>
+/// A Redis-backed <see cref="IQuickConnectStore"/> that lets the initiate, authorize and exchange legs
+/// of a quick connect flow land on different instances. Expiry is the key TTL, an authorization is
+/// claimed with a Lua check-and-set and consumed with <c>GETDEL</c>, so only one instance can ever mint
+/// a given secret's access token and only one can ever hand it out.
+/// </summary>
+/// <remarks>
+/// A pending request survives an unreachable Redis through a process-local fallback, because a second
+/// copy of it is harmless. An authorization has none: a second copy of it is a second access token, and
+/// a write whose response timed out may well have been applied, so a transport failure on that path is
+/// surfaced rather than degraded.
+/// </remarks>
+public sealed class RedisQuickConnectStore : IQuickConnectStore
+{
+    private const string KeyPrefix = "jellyfin:quickconnect:";
+
+    /// <summary>
+    /// Lua script for the atomic claim of the sole right to authorize a request: the request has to
+    /// exist and not already be authorized, and the claim marker is taken with <c>SET NX</c>, so of two
+    /// instances racing on one code exactly one goes on to mint an access token.
+    /// </summary>
+    private const string ClaimAuthorizationScript = @"
+local raw = redis.call('GET', KEYS[1])
+if not raw then return 0 end
+if cjson.decode(raw)['Authenticated'] then return 0 end
+if redis.call('SET', KEYS[2], '1', 'NX', 'PX', ARGV[1]) then return 1 end
+return 0";
+
+    private readonly IDatabase _db;
+    private readonly InMemoryQuickConnectStore _fallback;
+    private readonly ILogger<RedisQuickConnectStore> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RedisQuickConnectStore"/> class.
+    /// </summary>
+    /// <param name="redis">The Redis connection multiplexer.</param>
+    /// <param name="logger">The logger.</param>
+    public RedisQuickConnectStore(IConnectionMultiplexer redis, ILogger<RedisQuickConnectStore> logger)
+    {
+        ArgumentNullException.ThrowIfNull(redis);
+
+        _db = redis.GetDatabase();
+        _fallback = new InMemoryQuickConnectStore();
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public async Task<QuickConnectResult?> GetRequestBySecretAsync(string secret, CancellationToken cancellationToken = default)
+    {
+        RedisValue raw;
+        try
+        {
+            raw = await _db.StringGetAsync(RequestKey(secret)).ConfigureAwait(false);
+        }
+        catch (Exception ex) when (IsTransportFailure(ex))
+        {
+            LogDegraded(ex);
+            return await _fallback.GetRequestBySecretAsync(secret, cancellationToken).ConfigureAwait(false);
+        }
+
+        // A miss is an answer rather than a transport failure, so the fallback is not consulted for it.
+        return raw.HasValue ? JsonSerializer.Deserialize<QuickConnectResult>(raw.ToString(), JsonDefaults.Options) : null;
+    }
+
+    /// <inheritdoc />
+    public async Task<QuickConnectResult?> GetRequestByCodeAsync(string code, CancellationToken cancellationToken = default)
+    {
+        RedisValue secret;
+        try
+        {
+            secret = await _db.StringGetAsync(CodeKey(code)).ConfigureAwait(false);
+        }
+        catch (Exception ex) when (IsTransportFailure(ex))
+        {
+            LogDegraded(ex);
+            return await _fallback.GetRequestByCodeAsync(code, cancellationToken).ConfigureAwait(false);
+        }
+
+        return secret.HasValue
+            ? await GetRequestBySecretAsync(secret.ToString(), cancellationToken).ConfigureAwait(false)
+            : null;
+    }
+
+    /// <inheritdoc />
+    public async Task SetRequestAsync(QuickConnectResult request, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        var ttl = expiresUtc - DateTime.UtcNow;
+        if (ttl <= TimeSpan.Zero)
+        {
+            return;
+        }
+
+        try
+        {
+            var json = JsonSerializer.Serialize(request, JsonDefaults.Options);
+            await _db.StringSetAsync(RequestKey(request.Secret), json, ttl).ConfigureAwait(false);
+            await _db.StringSetAsync(CodeKey(request.Code), request.Secret, ttl).ConfigureAwait(false);
+        }
+        catch (Exception ex) when (IsTransportFailure(ex))
+        {
+            LogDegraded(ex);
+            await _fallback.SetRequestAsync(request, expiresUtc, cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    /// <inheritdoc />
+    public async Task<bool> TryClaimAuthorizationAsync(string secret, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        var ttl = expiresUtc - DateTime.UtcNow;
+        if (ttl <= TimeSpan.Zero)
+        {
+            return false;
+        }
+
+        var claimed = (long?)await _db.ScriptEvaluateAsync(
+            ClaimAuthorizationScript,
+            keys: new RedisKey[] { RequestKey(secret), ClaimKey(secret) },
+            values: new RedisValue[] { (long)ttl.TotalMilliseconds }).ConfigureAwait(false);
+
+        return claimed == 1;
+    }
+
+    /// <inheritdoc />
+    public async Task SetAuthorizationAsync(string secret, AuthenticationResult authenticationResult, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        var ttl = expiresUtc - DateTime.UtcNow;
+        if (ttl <= TimeSpan.Zero)
+        {
+            return;
+        }
+
+        var json = JsonSerializer.Serialize(authenticationResult, JsonDefaults.Options);
+        await _db.StringSetAsync(AuthorizationKey(secret), json, ttl).ConfigureAwait(false);
+    }
+
+    /// <inheritdoc />
+    public async Task<AuthenticationResult?> TryConsumeAuthorizationAsync(string secret, CancellationToken cancellationToken = default)
+    {
+        var raw = await _db.StringGetDeleteAsync(AuthorizationKey(secret)).ConfigureAwait(false);
+
+        return raw.HasValue
+            ? JsonSerializer.Deserialize<AuthenticationResult>(raw.ToString(), JsonDefaults.Options)
+            : null;
+    }
+
+    // Deliberately excludes a malformed stored value, which is a fault of its own rather than a reason
+    // to answer from this instance.
+    private static bool IsTransportFailure(Exception exception) => exception is RedisException or TimeoutException;
+
+    private static string RequestKey(string secret) => KeyPrefix + "request:" + secret;
+
+    private static string CodeKey(string code) => KeyPrefix + "code:" + code;
+
+    private static string ClaimKey(string secret) => KeyPrefix + "claim:" + secret;
+
+    private static string AuthorizationKey(string secret) => KeyPrefix + "auth:" + secret;
+
+    private void LogDegraded(Exception exception)
+        => _logger.LogWarning(exception, "Quick connect request state could not be shared through Redis; falling back to this instance only.");
+}

Emby.Server.Implementations/Sorting/DatePlayedComparer.cs

@@ -1,6 +1,7 @@
 #nullable disable
 
 using System;
+using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -27,6 +28,12 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
+        /// <summary>
+        /// Gets or sets the prefetched user data.
+        /// </summary>
+        /// <value>The prefetched user data.</value>
+        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
+
         /// <summary>
         /// Gets or sets the user data manager.
         /// </summary>
@@ -57,7 +64,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private DateTime GetDate(BaseItem x)
         {
-            var userdata = UserDataManager.GetUserData(User, x);
+            var userdata = this.GetUserData(x);
 
             if (userdata is not null && userdata.LastPlayedDate.HasValue)
             {

Emby.Server.Implementations/Sorting/IsFavoriteOrLikeComparer.cs

@@ -1,6 +1,8 @@
 #nullable disable
 #pragma warning disable CS1591
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -35,6 +37,12 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
+        /// <summary>
+        /// Gets or sets the prefetched user data.
+        /// </summary>
+        /// <value>The prefetched user data.</value>
+        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
+
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -53,7 +61,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsFavoriteOrLiked(User, userItemData: null) ? 0 : 1;
+            return x.IsFavoriteOrLiked(User, this.GetUserData(x)) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/IsPlayedComparer.cs

@@ -2,6 +2,8 @@
 
 #pragma warning disable CS1591
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -36,6 +38,12 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
+        /// <summary>
+        /// Gets or sets the prefetched user data.
+        /// </summary>
+        /// <value>The prefetched user data.</value>
+        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
+
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -54,7 +62,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsPlayed(User, userItemData: null) ? 0 : 1;
+            return x.IsPlayed(User, this.GetUserData(x)) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/IsUnplayedComparer.cs

@@ -2,6 +2,8 @@
 
 #pragma warning disable CS1591
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -36,6 +38,12 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
+        /// <summary>
+        /// Gets or sets the prefetched user data.
+        /// </summary>
+        /// <value>The prefetched user data.</value>
+        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
+
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -54,7 +62,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsUnplayed(User, userItemData: null) ? 0 : 1;
+            return x.IsUnplayed(User, this.GetUserData(x)) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/PlayCountComparer.cs

@@ -1,5 +1,7 @@
 #nullable disable
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -38,6 +40,12 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
+        /// <summary>
+        /// Gets or sets the prefetched user data.
+        /// </summary>
+        /// <value>The prefetched user data.</value>
+        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
+
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -56,7 +64,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            var userdata = UserDataManager.GetUserData(User, x);
+            var userdata = this.GetUserData(x);
 
             return userdata is null ? 0 : userdata.PlayCount;
         }

Emby.Server.Implementations/TV/TVSeriesManager.cs

@@ -13,6 +13,7 @@ using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Dto;
 using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
+using MediaBrowser.Controller.Persistence;
 using MediaBrowser.Controller.TV;
 using MediaBrowser.Model.Querying;
 using Episode = MediaBrowser.Controller.Entities.TV.Episode;
@@ -124,53 +125,100 @@ namespace Emby.Server.Implementations.TV
 
             var batchResult = _libraryManager.GetNextUpEpisodesBatch(query, seriesKeys, includeSpecials, includeRewatching);
 
-            var nextUpList = new List<(DateTime LastWatchedDate, Episode Episode)>();
-
+            var results = new List<NextUpEpisodeBatchResult>(seriesKeys.Count);
             foreach (var seriesKey in seriesKeys)
             {
-                if (!batchResult.TryGetValue(seriesKey, out var result))
+                if (batchResult.TryGetValue(seriesKey, out var result))
                 {
-                    continue;
+                    results.Add(result);
                 }
+            }
 
-                var nextEpisode = DetermineNextEpisode(result, user, includeSpecials, request.EnableResumable, false);
+            // The selection below tests the played state of every episode it considers, so read the whole
+            // series batch in one query rather than one query per series.
+            var selectionCandidates = new List<BaseItem>();
+            foreach (var result in results)
+            {
+                AddCandidate(selectionCandidates, result.NextUp);
+                AddCandidate(selectionCandidates, result.LastWatched);
+                AddCandidate(selectionCandidates, result.NextPlayedForRewatching);
+                AddCandidate(selectionCandidates, result.LastWatchedForRewatching);
 
+                if (result.Specials is not null)
+                {
+                    selectionCandidates.AddRange(result.Specials);
+                }
+            }
+
+            var selectionUserData = _userDataManager.GetUserDataBatch(selectionCandidates, user);
+
+            var candidates = new List<NextUpCandidate>();
+            foreach (var result in results)
+            {
+                var nextEpisode = SelectNextEpisode(result, user, includeSpecials, includePlayed: false, selectionUserData);
                 if (nextEpisode is not null)
                 {
-                    // The last played date and the version that was actually played live on the version item's user data
-                    // The played state propagated to the sibling versions carries no date
-                    var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(result.LastWatched, user);
-                    nextEpisode = GetPreferredVersion(nextEpisode, result.LastWatched, playedVersion);
-
-                    DateTime lastWatchedDate = DateTime.MinValue;
-                    if (result.LastWatched is not null)
-                    {
-                        lastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
-                    }
-
-                    nextUpList.Add((lastWatchedDate, nextEpisode));
+                    candidates.Add(new NextUpCandidate(nextEpisode, result.LastWatched, !request.EnableResumable));
                 }
 
                 if (includeRewatching)
                 {
-                    var nextPlayedEpisode = DetermineNextEpisodeForRewatching(result, user, includeSpecials);
-
+                    var nextPlayedEpisode = SelectNextEpisode(result, user, includeSpecials, includePlayed: true, selectionUserData);
                     if (nextPlayedEpisode is not null)
                     {
-                        var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(result.LastWatchedForRewatching, user);
-                        nextPlayedEpisode = GetPreferredVersion(nextPlayedEpisode, result.LastWatchedForRewatching, playedVersion);
-
-                        DateTime rewatchLastWatchedDate = DateTime.MinValue;
-                        if (result.LastWatchedForRewatching is not null)
-                        {
-                            rewatchLastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
-                        }
-
-                        nextUpList.Add((rewatchLastWatchedDate, nextPlayedEpisode));
+                        // A rewatch suggestion is dropped once it has been resumed, whatever the request asked for.
+                        candidates.Add(new NextUpCandidate(nextPlayedEpisode, result.LastWatchedForRewatching, true));
                     }
                 }
             }
 
+            // The resume progress may live on an alternate version, so read every version in one query.
+            var episodeVersions = new List<BaseItem>();
+            foreach (var candidate in candidates)
+            {
+                if (candidate.DropWhenResumed)
+                {
+                    candidate.EpisodeVersions = candidate.Episode.GetAllVersions();
+                    episodeVersions.AddRange(candidate.EpisodeVersions);
+                }
+            }
+
+            if (episodeVersions.Count > 0)
+            {
+                var resumeUserData = _userDataManager.GetUserDataBatch(episodeVersions, user);
+                candidates.RemoveAll(candidate => candidate.EpisodeVersions
+                    .Any(version => GetUserData(user, version, resumeUserData)?.PlaybackPositionTicks > 0));
+            }
+
+            // The last played date and the version that was actually played live on the version item's user data
+            // The played state propagated to the sibling versions carries no date
+            var lastWatchedVersions = new List<BaseItem>();
+            foreach (var candidate in candidates)
+            {
+                if (candidate.LastWatched is Video lastWatchedVideo)
+                {
+                    candidate.LastWatchedVersions = lastWatchedVideo.GetAllVersions();
+                    lastWatchedVersions.AddRange(candidate.LastWatchedVersions);
+                }
+            }
+
+            var lastWatchedUserData = _userDataManager.GetUserDataBatch(lastWatchedVersions, user);
+
+            var nextUpList = new List<(DateTime LastWatchedDate, Episode Episode)>(candidates.Count);
+            foreach (var candidate in candidates)
+            {
+                var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(candidate.LastWatchedVersions, user, lastWatchedUserData);
+                var nextEpisode = GetPreferredVersion(candidate.Episode, candidate.LastWatched, playedVersion);
+
+                DateTime lastWatchedDate = DateTime.MinValue;
+                if (candidate.LastWatched is not null)
+                {
+                    lastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
+                }
+
+                nextUpList.Add((lastWatchedDate, nextEpisode));
+            }
+
             var sortedEpisodes = nextUpList
                 .OrderByDescending(x => x.LastWatchedDate)
                 .Select(x => (BaseItem)x.Episode);
@@ -178,12 +226,25 @@ namespace Emby.Server.Implementations.TV
             return GetResult(sortedEpisodes, request);
         }
 
-        private Episode? DetermineNextEpisode(
-            MediaBrowser.Controller.Persistence.NextUpEpisodeBatchResult result,
+        private static void AddCandidate(List<BaseItem> candidates, BaseItem? item)
+        {
+            if (item is not null)
+            {
+                candidates.Add(item);
+            }
+        }
+
+        private UserItemData? GetUserData(User user, BaseItem item, IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
+            => prefetchedUserData.TryGetValue(item.Id, out var userData)
+                ? userData
+                : _userDataManager.GetUserData(user, item);
+
+        private Episode? SelectNextEpisode(
+            NextUpEpisodeBatchResult result,
             User user,
             bool includeSpecials,
-            bool includeResumable,
-            bool includePlayed)
+            bool includePlayed,
+            IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
         {
             var nextEpisode = (includePlayed ? result.NextPlayedForRewatching : result.NextUp) as Episode;
             var lastWatchedEpisode = (includePlayed ? result.LastWatchedForRewatching : result.LastWatched) as Episode;
@@ -217,60 +278,41 @@ namespace Emby.Server.Implementations.TV
 
                     if (!includePlayed)
                     {
-                        sortedEpisodes = sortedEpisodes.Where(episode => _userDataManager.GetUserData(user, episode) is not { Played: true });
+                        sortedEpisodes = sortedEpisodes.Where(episode => GetUserData(user, episode, prefetchedUserData) is not { Played: true });
                     }
 
                     nextEpisode = sortedEpisodes.FirstOrDefault();
                 }
             }
 
-            if (nextEpisode is not null && !includeResumable)
-            {
-                // The resume progress may live on an alternate version
-                foreach (var version in nextEpisode.GetAllVersions())
-                {
-                    if (_userDataManager.GetUserData(user, version)?.PlaybackPositionTicks > 0)
-                    {
-                        return null;
-                    }
-                }
-            }
-
             return nextEpisode;
         }
 
-        private Episode? DetermineNextEpisodeForRewatching(
-            MediaBrowser.Controller.Persistence.NextUpEpisodeBatchResult result,
-            User user,
-            bool includeSpecials)
-        {
-            return DetermineNextEpisode(result, user, includeSpecials, includeResumable: false, includePlayed: true);
-        }
-
         /// <summary>
         /// Gets the version of the last watched episode that was actually played, together with its last played date.
         /// The version that was played carries the most recent LastPlayedDate.
         /// dates.
         /// </summary>
-        /// <param name="lastWatched">The last watched episode (any version).</param>
+        /// <param name="versions">The versions of the last watched episode.</param>
         /// <param name="user">The user.</param>
+        /// <param name="prefetchedUserData">User data read for every version up front.</param>
         /// <returns>The played version and its last played date.</returns>
-        private (Video? PlayedVersion, DateTime? LastPlayedDate) GetMostRecentlyPlayedVersion(BaseItem? lastWatched, User user)
+        private (Video? PlayedVersion, DateTime? LastPlayedDate) GetMostRecentlyPlayedVersion(
+            IReadOnlyList<Video> versions,
+            User user,
+            IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
         {
-            if (lastWatched is not Video lastWatchedVideo)
+            if (versions.Count == 0)
             {
                 return (null, null);
             }
 
-            var versions = lastWatchedVideo.GetAllVersions();
-            var userDataByVersion = _userDataManager.GetUserDataBatch(versions, user);
-
             var playedVersion = VersionPlaybackSelector.SelectMostRecentlyPlayed(
                 versions,
-                version => userDataByVersion.GetValueOrDefault(version.Id),
+                version => GetUserData(user, version, prefetchedUserData),
                 data => data.LastPlayedDate.HasValue);
 
-            return (playedVersion, playedVersion is null ? null : userDataByVersion[playedVersion.Id].LastPlayedDate);
+            return (playedVersion, playedVersion is null ? null : GetUserData(user, playedVersion, prefetchedUserData)?.LastPlayedDate);
         }
 
         /// <summary>
@@ -346,5 +388,28 @@ namespace Emby.Server.Implementations.TV
                 totalCount,
                 items.ToArray());
         }
+
+        /// <summary>
+        /// An episode picked for Next Up, together with the versions its user data is read from.
+        /// </summary>
+        private sealed class NextUpCandidate
+        {
+            public NextUpCandidate(Episode episode, BaseItem? lastWatched, bool dropWhenResumed)
+            {
+                Episode = episode;
+                LastWatched = lastWatched;
+                DropWhenResumed = dropWhenResumed;
+            }
+
+            public Episode Episode { get; }
+
+            public BaseItem? LastWatched { get; }
+
+            public bool DropWhenResumed { get; }
+
+            public IReadOnlyList<Video> EpisodeVersions { get; set; } = [];
+
+            public IReadOnlyList<Video> LastWatchedVersions { get; set; } = [];
+        }
     }
 }

Jellyfin.Api/Controllers/QuickConnectController.cs

@@ -59,7 +59,7 @@ public class QuickConnectController : BaseJellyfinApiController
         try
         {
             var auth = await _authContext.GetAuthorizationInfo(Request).ConfigureAwait(false);
-            return _quickConnect.TryConnect(auth);
+            return await _quickConnect.TryConnect(auth).ConfigureAwait(false);
         }
         catch (AuthenticationException)
         {
@@ -77,11 +77,11 @@ public class QuickConnectController : BaseJellyfinApiController
     [HttpGet("Connect")]
     [ProducesResponseType(StatusCodes.Status200OK)]
     [ProducesResponseType(StatusCodes.Status404NotFound)]
-    public ActionResult<QuickConnectResult> GetQuickConnectState([FromQuery, Required] string secret)
+    public async Task<ActionResult<QuickConnectResult>> GetQuickConnectState([FromQuery, Required] string secret)
     {
         try
         {
-            return _quickConnect.CheckRequestStatus(secret);
+            return await _quickConnect.CheckRequestStatus(secret).ConfigureAwait(false);
         }
         catch (ResourceNotFoundException)
         {

Jellyfin.Api/Controllers/TvShowsController.cs

@@ -108,7 +108,7 @@ public class TvShowsController : BaseJellyfinApiController
                 StartIndex = startIndex,
                 User = user,
                 EnableTotalRecordCount = enableTotalRecordCount,
-                NextUpDateCutoff = nextUpDateCutoff ?? DateTime.MinValue,
+                NextUpDateCutoff = nextUpDateCutoff?.ToUniversalTime() ?? DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc),
                 EnableResumable = enableResumable,
                 EnableRewatching = enableRewatching
             },

Jellyfin.Api/Controllers/UserController.cs

@@ -245,11 +245,11 @@ public class UserController : BaseJellyfinApiController
     [HttpPost("AuthenticateWithQuickConnect")]
     [ProducesResponseType(StatusCodes.Status200OK)]
     [Tags("Authentication")]
-    public ActionResult<AuthenticationResult> AuthenticateWithQuickConnect([FromBody, Required] QuickConnectDto request)
+    public async Task<ActionResult<AuthenticationResult>> AuthenticateWithQuickConnect([FromBody, Required] QuickConnectDto request)
     {
         try
         {
-            return _quickConnectManager.GetAuthorizedRequest(request.Secret);
+            return await _quickConnectManager.GetAuthorizedRequest(request.Secret).ConfigureAwait(false);
         }
         catch (SecurityException e)
         {

Jellyfin.Server/CoreAppHost.cs

@@ -112,6 +112,14 @@ namespace Jellyfin.Server
             // instance. Active by default once a Redis connection is configured, no-op otherwise.
             serviceCollection.AddScanLeaderLease(_startupConfig, Logger);
 
+            // Configuration invalidation bus: propagates shared-configuration and library-option writes
+            // to the other instances. Redis-backed when configured, no-op otherwise.
+            serviceCollection.AddConfigurationInvalidationBus(_startupConfig, Logger);
+
+            // Quick connect store: shares in-flight quick connect requests so the initiate, authorize and
+            // exchange legs can land on different instances. Redis-backed when configured, local otherwise.
+            serviceCollection.AddQuickConnectStore(_startupConfig, Logger);
+
             foreach (var type in GetExportTypes<ILyricProvider>())
             {
                 serviceCollection.AddSingleton(typeof(ILyricProvider), type);

Jellyfin.Server/Extensions/ConfigurationInvalidationServiceCollectionExtensions.cs

@@ -0,0 +1,74 @@
+using System;
+using Emby.Server.Implementations.Configuration;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.MediaEncoding;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Jellyfin.Server.Extensions;
+
+/// <summary>
+/// Extensions for registering the shared-configuration invalidation bus.
+/// </summary>
+public static class ConfigurationInvalidationServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers the invalidation bus, Redis-backed when a connection string is configured and no-op
+    /// otherwise, and the subscriber applying the notices other instances publish.
+    /// </summary>
+    /// <remarks>
+    /// The connection string is only set for a multi-instance deployment, which is the only shape where
+    /// one instance can write the shared configuration directory behind another's back.
+    /// </remarks>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <param name="configuration">The configuration to read the Redis connection string from.</param>
+    /// <param name="logger">The logger to report the selected bus on.</param>
+    /// <returns>The updated service collection.</returns>
+    public static IServiceCollection AddConfigurationInvalidationBus(
+        this IServiceCollection serviceCollection,
+        IConfiguration configuration,
+        ILogger logger)
+    {
+        ArgumentNullException.ThrowIfNull(configuration);
+        ArgumentNullException.ThrowIfNull(logger);
+
+        if (string.IsNullOrEmpty(configuration[TranscodeStoreOptions.RedisConnectionStringKey]))
+        {
+            logger.LogInformation(
+                "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes stay local to the instance that made them; set {Key} to propagate them.",
+                nameof(NullConfigurationInvalidationBus),
+                TranscodeStoreOptions.RedisConnectionStringKey);
+
+            return serviceCollection.AddSingleton<IConfigurationInvalidationBus>(NullConfigurationInvalidationBus.Instance);
+        }
+
+        logger.LogInformation(
+            "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes propagate to every instance.",
+            nameof(RedisConfigurationInvalidationBus));
+
+        serviceCollection.AddSingleton<IConfigurationInvalidationBus>(sp =>
+        {
+            try
+            {
+                return new RedisConfigurationInvalidationBus(
+                    sp.GetRequiredService<IConnectionMultiplexer>(),
+                    sp.GetRequiredService<ILogger<RedisConfigurationInvalidationBus>>());
+            }
+            catch (Exception ex)
+            {
+                // Fail open: an unreachable Redis degrades to the single-instance behaviour of every
+                // instance keeping its own cached configuration, rather than aborting startup.
+                sp.GetRequiredService<ILogger<CoreAppHost>>().LogError(
+                    ex,
+                    "Redis is configured but unavailable, so shared-configuration changes will not propagate between instances. Check {Key}.",
+                    TranscodeStoreOptions.RedisConnectionStringKey);
+
+                return NullConfigurationInvalidationBus.Instance;
+            }
+        });
+
+        return serviceCollection.AddHostedService<ConfigurationInvalidationSubscriber>();
+    }
+}

Jellyfin.Server/Extensions/QuickConnectStoreServiceCollectionExtensions.cs

@@ -0,0 +1,72 @@
+using System;
+using Emby.Server.Implementations.QuickConnect;
+using MediaBrowser.Controller.MediaEncoding;
+using MediaBrowser.Controller.QuickConnect;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Jellyfin.Server.Extensions;
+
+/// <summary>
+/// Extensions for registering the quick connect store.
+/// </summary>
+public static class QuickConnectStoreServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers the quick connect store, Redis-backed when a connection string is configured and
+    /// process-local otherwise, and reports the selected store at <see cref="LogLevel.Information"/>.
+    /// </summary>
+    /// <remarks>
+    /// The connection string is only set for a multi-instance deployment, which is the only shape where
+    /// the initiate, authorize and exchange legs of one flow can land on different instances.
+    /// </remarks>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <param name="configuration">The configuration to read the Redis connection string from.</param>
+    /// <param name="logger">The logger to report the selected store on.</param>
+    /// <returns>The updated service collection.</returns>
+    public static IServiceCollection AddQuickConnectStore(
+        this IServiceCollection serviceCollection,
+        IConfiguration configuration,
+        ILogger logger)
+    {
+        ArgumentNullException.ThrowIfNull(configuration);
+        ArgumentNullException.ThrowIfNull(logger);
+
+        if (string.IsNullOrEmpty(configuration[TranscodeStoreOptions.RedisConnectionStringKey]))
+        {
+            logger.LogInformation(
+                "Quick connect store: {Store}. A quick connect flow has to complete against one instance; set {Key} to share it.",
+                nameof(InMemoryQuickConnectStore),
+                TranscodeStoreOptions.RedisConnectionStringKey);
+
+            return serviceCollection.AddSingleton<IQuickConnectStore, InMemoryQuickConnectStore>();
+        }
+
+        logger.LogInformation(
+            "Quick connect store: {Store}. Quick connect flows complete across any instance.",
+            nameof(RedisQuickConnectStore));
+
+        return serviceCollection.AddSingleton<IQuickConnectStore>(sp =>
+        {
+            try
+            {
+                return new RedisQuickConnectStore(
+                    sp.GetRequiredService<IConnectionMultiplexer>(),
+                    sp.GetRequiredService<ILogger<RedisQuickConnectStore>>());
+            }
+            catch (Exception ex)
+            {
+                // Fail open: an unreachable Redis degrades to the single-instance behaviour of a flow
+                // having to complete against one instance, rather than taking quick connect down.
+                sp.GetRequiredService<ILogger<CoreAppHost>>().LogError(
+                    ex,
+                    "Redis is configured but unavailable, so quick connect flows will not complete across instances. Check {Key}.",
+                    TranscodeStoreOptions.RedisConnectionStringKey);
+
+                return new InMemoryQuickConnectStore();
+            }
+        });
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidation.cs

@@ -0,0 +1,26 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// A notice that one instance has written shared configuration, so every other instance has to drop
+    /// its locally cached copy and read the shared file again.
+    /// </summary>
+    public sealed class ConfigurationInvalidation
+    {
+        /// <summary>
+        /// Gets or sets the cache this notice refers to.
+        /// </summary>
+        public ConfigurationInvalidationScope Scope { get; set; }
+
+        /// <summary>
+        /// Gets or sets what was invalidated within the scope: the configuration key for
+        /// <see cref="ConfigurationInvalidationScope.NamedConfiguration"/>, the library path for
+        /// <see cref="ConfigurationInvalidationScope.LibraryOptions"/>, and <c>null</c> otherwise.
+        /// </summary>
+        public string? Target { get; set; }
+
+        /// <summary>
+        /// Gets or sets the identity of the instance that published the notice, so it can ignore its own.
+        /// </summary>
+        public string? OriginId { get; set; }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationBusExtensions.cs

@@ -0,0 +1,30 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Extensions for <see cref="IConfigurationInvalidationBus"/>.
+    /// </summary>
+    public static class ConfigurationInvalidationBusExtensions
+    {
+        /// <summary>
+        /// Announces a write this instance originated, and stays silent for a write induced by an
+        /// invalidation another instance published.
+        /// </summary>
+        /// <remarks>
+        /// This is the backstop for the write path: a consumer reacting to an applied invalidation by
+        /// writing - including a plugin that knows nothing about the bus - cannot turn that write into a
+        /// notice of its own.
+        /// </remarks>
+        /// <param name="bus">The bus.</param>
+        /// <param name="scope">The cache that was written.</param>
+        /// <param name="target">The configuration key or library path that was written, if any.</param>
+        public static void PublishLocalWrite(this IConfigurationInvalidationBus bus, ConfigurationInvalidationScope scope, string? target)
+        {
+            if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+            {
+                return;
+            }
+
+            bus.Publish(scope, target);
+        }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationContext.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Threading;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Marks the flow of control that is applying an invalidation published by another instance, so the
+    /// reactions to it can tell a remote write apart from a local one.
+    /// </summary>
+    /// <remarks>
+    /// Applying an invalidation raises the same update events a local save raises, because the in-process
+    /// consumers have to re-read the configuration either way. Some of those consumers answer an update by
+    /// writing, and that write must neither repeat what the publishing instance already did nor fan back
+    /// out over the bus. The flag rides the execution context, so it reaches the queued and asynchronous
+    /// event handlers as well as the synchronous ones.
+    /// </remarks>
+    public static class ConfigurationInvalidationContext
+    {
+        private static readonly AsyncLocal<bool> _applyingRemoteInvalidation = new();
+
+        /// <summary>
+        /// Gets a value indicating whether the current flow of control is applying an invalidation
+        /// published by another instance rather than handling a local save.
+        /// </summary>
+        public static bool IsApplyingRemoteInvalidation => _applyingRemoteInvalidation.Value;
+
+        /// <summary>
+        /// Marks the current flow of control as applying a remote invalidation until the returned scope is
+        /// disposed.
+        /// </summary>
+        /// <returns>The scope to dispose once the invalidation has been applied.</returns>
+        public static IDisposable BeginApply() => new ApplyScope();
+
+        private sealed class ApplyScope : IDisposable
+        {
+            private readonly bool _previous;
+            private bool _disposed;
+
+            public ApplyScope()
+            {
+                _previous = _applyingRemoteInvalidation.Value;
+                _applyingRemoteInvalidation.Value = true;
+            }
+
+            public void Dispose()
+            {
+                if (_disposed)
+                {
+                    return;
+                }
+
+                _disposed = true;
+                _applyingRemoteInvalidation.Value = _previous;
+            }
+        }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationScope.cs

@@ -0,0 +1,29 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Identifies which locally cached copy of the shared configuration a
+    /// <see cref="ConfigurationInvalidation"/> refers to.
+    /// </summary>
+    public enum ConfigurationInvalidationScope
+    {
+        /// <summary>
+        /// The system configuration cached by the configuration manager.
+        /// </summary>
+        SystemConfiguration = 0,
+
+        /// <summary>
+        /// A single named configuration, identified by its key.
+        /// </summary>
+        NamedConfiguration = 1,
+
+        /// <summary>
+        /// The library options of a single collection folder, identified by its path.
+        /// </summary>
+        LibraryOptions = 2,
+
+        /// <summary>
+        /// The library options of every collection folder, for changes to the library structure itself.
+        /// </summary>
+        AllLibraryOptions = 3
+    }
+}

MediaBrowser.Common/Configuration/IConfigurationInvalidationBus.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Carries cache-invalidation notices between the instances that share one configuration directory.
+    /// </summary>
+    /// <remarks>
+    /// The shared directory carries the content; this bus only carries the fact that it changed. Every
+    /// implementation is expected to fail open: a bus that cannot deliver must not throw into the write
+    /// path, leaving each instance on its own locally cached copy until it restarts.
+    /// </remarks>
+    public interface IConfigurationInvalidationBus
+    {
+        /// <summary>
+        /// Announces that this instance has written shared configuration.
+        /// </summary>
+        /// <param name="scope">The cache that was written.</param>
+        /// <param name="target">The configuration key or library path that was written, if any.</param>
+        void Publish(ConfigurationInvalidationScope scope, string? target);
+
+        /// <summary>
+        /// Registers the handler invoked for notices published by other instances.
+        /// </summary>
+        /// <param name="handler">The handler applying the invalidation locally.</param>
+        void Subscribe(Action<ConfigurationInvalidation> handler);
+    }
+}

MediaBrowser.Common/Configuration/IConfigurationManager.cs

@@ -85,6 +85,20 @@ namespace MediaBrowser.Common.Configuration
         /// </summary>
         /// <param name="factories">The factories.</param>
         void AddParts(IEnumerable<IConfigurationFactory> factories);
+
+        /// <summary>
+        /// Drops the locally cached copy of configuration another instance has written to the shared
+        /// configuration directory, so the next read reloads it, and raises the local update event.
+        /// </summary>
+        /// <remarks>
+        /// An implementation predating the invalidation bus keeps the default, which reports that it
+        /// cannot drop its cache rather than quietly leaving it stale. The caller applying a remote
+        /// notice treats that as a failed apply and logs it.
+        /// </remarks>
+        /// <param name="key">The named configuration key, or <c>null</c> for the system configuration.</param>
+        /// <exception cref="NotSupportedException">The implementation cannot drop its cached configuration.</exception>
+        void InvalidateCachedConfiguration(string? key)
+            => throw new NotSupportedException(GetType().Name + " cannot drop configuration cached from the shared configuration directory, so writes by other instances will not be picked up.");
     }
 
     public static class ConfigurationManagerExtensions

MediaBrowser.Common/Configuration/NullConfigurationInvalidationBus.cs

@@ -0,0 +1,27 @@
+using System;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// A no-op <see cref="IConfigurationInvalidationBus"/> used by single-instance installs and whenever
+    /// the shared bus is unavailable. Every instance keeps its own cached configuration, which is the
+    /// behaviour of an install that has only one.
+    /// </summary>
+    public sealed class NullConfigurationInvalidationBus : IConfigurationInvalidationBus
+    {
+        /// <summary>
+        /// Gets the shared instance.
+        /// </summary>
+        public static NullConfigurationInvalidationBus Instance { get; } = new NullConfigurationInvalidationBus();
+
+        /// <inheritdoc />
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+        {
+        }
+
+        /// <inheritdoc />
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+        {
+        }
+    }
+}

MediaBrowser.Controller/Entities/CollectionFolder.cs

@@ -14,6 +14,7 @@ using System.Threading.Tasks;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Configuration;
 using MediaBrowser.Controller.IO;
 using MediaBrowser.Controller.Library;
 using MediaBrowser.Controller.Providers;
@@ -70,6 +71,12 @@ namespace MediaBrowser.Controller.Entities
 
         public static IServerApplicationHost ApplicationHost { get; set; }
 
+        /// <summary>
+        /// Gets or sets the bus announcing library option writes to the other instances sharing this
+        /// configuration directory. Defaults to a no-op, which is the single-instance behaviour.
+        /// </summary>
+        public static IConfigurationInvalidationBus InvalidationBus { get; set; } = NullConfigurationInvalidationBus.Instance;
+
         [JsonIgnore]
         public override bool SupportsPlayedStatus => false;
 
@@ -188,11 +195,36 @@ namespace MediaBrowser.Controller.Entities
             XmlSerializer.SerializeToFile(clone, GetLibraryOptionsPath(path));
 
             LibraryOptionsUpdated?.Invoke(null, new LibraryOptionsUpdatedEventArgs(path, options));
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.LibraryOptions, path);
         }
 
-        public static void OnCollectionFolderChange()
+        /// <summary>
+        /// Drops the cached options of one library so the next read comes off <c>options.xml</c> again.
+        /// Applied on the instances that did not write, and so does not publish.
+        /// </summary>
+        /// <param name="path">The library path.</param>
+        public static void InvalidateLibraryOptions(string path)
+        {
+            _libraryOptions.TryRemove(path, out _);
+
+            LibraryOptionsUpdated?.Invoke(null, new LibraryOptionsUpdatedEventArgs(path, GetLibraryOptions(path)));
+        }
+
+        /// <summary>
+        /// Drops every cached library option set. Applied on the instances that did not write, and so does
+        /// not publish.
+        /// </summary>
+        public static void InvalidateAllLibraryOptions()
             => _libraryOptions.Clear();
 
+        public static void OnCollectionFolderChange()
+        {
+            InvalidateAllLibraryOptions();
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.AllLibraryOptions, null);
+        }
+
         public override bool IsSaveLocalMetadataEnabled()
         {
             return true;

MediaBrowser.Controller/Entities/UserViewBuilder.cs

@@ -449,19 +449,26 @@ namespace MediaBrowser.Controller.Entities
             IUserDataManager userDataManager,
             ILibraryManager libraryManager)
         {
-            var filtered = items.Where(i => Filter(i, user, query, userDataManager, libraryManager));
+            var itemList = items as IReadOnlyList<BaseItem> ?? items.ToList();
+
+            // The user data checks below run per item, so read them all in one query up front.
+            var userDataBatch = user is not null && RequiresUserData(query)
+                ? userDataManager.GetUserDataBatch(itemList, user)
+                : null;
+
+            var filtered = itemList.Where(i => Filter(i, user, query, userDataManager, libraryManager, userDataBatch));
 
             if (query.IsPlayed.HasValue && user is not null)
             {
-                var itemList = filtered.ToList();
-                var folderIds = itemList.OfType<Folder>().Select(f => f.Id).ToList();
+                var filteredList = filtered.ToList();
+                var folderIds = filteredList.OfType<Folder>().Select(f => f.Id).ToList();
 
                 if (folderIds.Count > 0)
                 {
                     var counts = libraryManager.GetPlayedAndTotalCountBatch(folderIds, user);
                     var isPlayedValue = query.IsPlayed.Value;
 
-                    return itemList.Where(item =>
+                    return filteredList.Where(item =>
                     {
                         if (item is Folder)
                         {
@@ -473,7 +480,7 @@ namespace MediaBrowser.Controller.Entities
                     });
                 }
 
-                return itemList;
+                return filteredList;
             }
 
             return filtered;
@@ -515,12 +522,29 @@ namespace MediaBrowser.Controller.Entities
                 itemsArray);
         }
 
+        private static bool RequiresUserData(InternalItemsQuery query)
+            => query.IsLiked.HasValue
+                || query.IsFavoriteOrLiked.HasValue
+                || query.IsFavorite.HasValue
+                || query.IsResumable.HasValue
+                || query.IsPlayed.HasValue;
+
+        private static UserItemData GetUserData(
+            IUserDataManager userDataManager,
+            User user,
+            BaseItem item,
+            Dictionary<Guid, UserItemData> userDataBatch)
+            => userDataBatch is not null && userDataBatch.TryGetValue(item.Id, out var userData)
+                ? userData
+                : userDataManager.GetUserData(user, item);
+
         private static bool Filter(
             BaseItem item,
             User user,
             InternalItemsQuery query,
             IUserDataManager userDataManager,
-            ILibraryManager libraryManager)
+            ILibraryManager libraryManager,
+            Dictionary<Guid, UserItemData> userDataBatch)
         {
             if (!string.IsNullOrEmpty(query.NameStartsWith) && !item.SortName.StartsWith(query.NameStartsWith, StringComparison.InvariantCultureIgnoreCase))
             {
@@ -568,7 +592,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsLiked.HasValue)
             {
-                userData = userDataManager.GetUserData(user, item);
+                userData = GetUserData(userDataManager, user, item, userDataBatch);
                 if (!userData.Likes.HasValue || userData.Likes != query.IsLiked.Value)
                 {
                     return false;
@@ -577,7 +601,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsFavoriteOrLiked.HasValue)
             {
-                userData ??= userDataManager.GetUserData(user, item);
+                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
                 var isFavoriteOrLiked = userData.IsFavorite || (userData.Likes ?? false);
 
                 if (isFavoriteOrLiked != query.IsFavoriteOrLiked.Value)
@@ -588,7 +612,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsFavorite.HasValue)
             {
-                userData ??= userDataManager.GetUserData(user, item);
+                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
                 if (userData.IsFavorite != query.IsFavorite.Value)
                 {
                     return false;
@@ -597,7 +621,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsResumable.HasValue)
             {
-                userData ??= userDataManager.GetUserData(user, item);
+                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
                 var isResumable = userData.PlaybackPositionTicks > 0;
 
                 if (isResumable != query.IsResumable.Value)
@@ -612,7 +636,7 @@ namespace MediaBrowser.Controller.Entities
                 // Folders are batch-filtered by the collection Filter() overload.
                 if (!item.IsFolder)
                 {
-                    userData ??= userDataManager.GetUserData(user, item);
+                    userData ??= GetUserData(userDataManager, user, item, userDataBatch);
                     if (item.IsPlayed(user, userData) != query.IsPlayed.Value)
                     {
                         return false;

MediaBrowser.Controller/QuickConnect/IQuickConnect.cs

@@ -21,14 +21,14 @@ namespace MediaBrowser.Controller.QuickConnect
         /// </summary>
         /// <param name="authorizationInfo">The initiator authorization info.</param>
         /// <returns>A quick connect result with tokens to proceed or throws an exception if not active.</returns>
-        QuickConnectResult TryConnect(AuthorizationInfo authorizationInfo);
+        Task<QuickConnectResult> TryConnect(AuthorizationInfo authorizationInfo);
 
         /// <summary>
         /// Checks the status of an individual request.
         /// </summary>
         /// <param name="secret">Unique secret identifier of the request.</param>
         /// <returns>Quick connect result.</returns>
-        QuickConnectResult CheckRequestStatus(string secret);
+        Task<QuickConnectResult> CheckRequestStatus(string secret);
 
         /// <summary>
         /// Authorizes a quick connect request to connect as the calling user.
@@ -43,6 +43,6 @@ namespace MediaBrowser.Controller.QuickConnect
         /// </summary>
         /// <param name="secret">The secret.</param>
         /// <returns>The authentication result.</returns>
-        AuthenticationResult GetAuthorizedRequest(string secret);
+        Task<AuthenticationResult> GetAuthorizedRequest(string secret);
     }
 }

MediaBrowser.Controller/QuickConnect/IQuickConnectStore.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Model.QuickConnect;
+
+namespace MediaBrowser.Controller.QuickConnect;
+
+/// <summary>
+/// Holds the state of in-flight quick connect requests. The three legs of a quick connect flow -
+/// initiate, authorize and exchange - can each land on a different instance, so the state has to be
+/// reachable from all of them.
+/// </summary>
+public interface IQuickConnectStore
+{
+    /// <summary>
+    /// Looks up a pending request by the secret handed to the initiating client.
+    /// </summary>
+    /// <param name="secret">The request secret.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>The request, or <c>null</c> when it is unknown or has expired.</returns>
+    Task<QuickConnectResult?> GetRequestBySecretAsync(string secret, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Looks up a pending request by the code shown to the user.
+    /// </summary>
+    /// <param name="code">The user facing code.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>The request, or <c>null</c> when it is unknown or has expired.</returns>
+    Task<QuickConnectResult?> GetRequestByCodeAsync(string code, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Stores a new or updated request until <paramref name="expiresUtc"/>.
+    /// </summary>
+    /// <param name="request">The request to store.</param>
+    /// <param name="expiresUtc">The instant the request stops being resolvable.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    Task SetRequestAsync(QuickConnectResult request, DateTime expiresUtc, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Atomically claims the sole right to authorize the request behind <paramref name="secret"/>, so
+    /// that two instances racing on one code cannot both mint an access token. The claim is never
+    /// released: a mint that failed after writing its token would otherwise be retried into a second one.
+    /// </summary>
+    /// <param name="secret">The request secret.</param>
+    /// <param name="expiresUtc">The instant the claim lapses, after which the request can be authorized again.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns><c>true</c> when this caller may go on to authorize the request; <c>false</c> when it is unknown, expired, already authorized or being authorized elsewhere.</returns>
+    Task<bool> TryClaimAuthorizationAsync(string secret, DateTime expiresUtc, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Stores the authentication minted for an authorized request until <paramref name="expiresUtc"/>.
+    /// </summary>
+    /// <param name="secret">The request secret the client exchanges.</param>
+    /// <param name="authenticationResult">The authentication to hand out.</param>
+    /// <param name="expiresUtc">The instant the authentication stops being exchangeable.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    Task SetAuthorizationAsync(string secret, AuthenticationResult authenticationResult, DateTime expiresUtc, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Atomically takes the authentication for <paramref name="secret"/> and removes it, so that two
+    /// instances racing on the same secret cannot both hand out an access token.
+    /// </summary>
+    /// <param name="secret">The request secret.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>The authentication, or <c>null</c> when the secret is unknown, expired or already exchanged.</returns>
+    Task<AuthenticationResult?> TryConsumeAuthorizationAsync(string secret, CancellationToken cancellationToken = default);
+}

MediaBrowser.Controller/QuickConnect/InMemoryQuickConnectStore.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Collections.Concurrent;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Model.QuickConnect;
+
+namespace MediaBrowser.Controller.QuickConnect;
+
+/// <summary>
+/// A process-local <see cref="IQuickConnectStore"/>. It is the single-instance default, and the
+/// fallback a shared store degrades to while its backend is unreachable, so quick connect keeps
+/// working for clients whose three legs happen to land on one instance.
+/// </summary>
+public sealed class InMemoryQuickConnectStore : IQuickConnectStore
+{
+    private readonly ConcurrentDictionary<string, Entry<QuickConnectResult>> _requests = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<string, Entry<AuthenticationResult>> _authorizations = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<string, DateTime> _authorizationClaims = new(StringComparer.Ordinal);
+
+    /// <inheritdoc />
+    public Task<QuickConnectResult?> GetRequestBySecretAsync(string secret, CancellationToken cancellationToken = default)
+    {
+        Expire();
+        return Task.FromResult(_requests.TryGetValue(secret, out var entry) ? entry.Value : null);
+    }
+
+    /// <inheritdoc />
+    public Task<QuickConnectResult?> GetRequestByCodeAsync(string code, CancellationToken cancellationToken = default)
+    {
+        Expire();
+        return Task.FromResult(_requests.Values
+            .Select(entry => entry.Value)
+            .FirstOrDefault(request => string.Equals(request.Code, code, StringComparison.Ordinal)));
+    }
+
+    /// <inheritdoc />
+    public Task SetRequestAsync(QuickConnectResult request, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        Expire();
+        _requests[request.Secret] = new Entry<QuickConnectResult>(expiresUtc, request);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task<bool> TryClaimAuthorizationAsync(string secret, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        Expire();
+        if (!_requests.TryGetValue(secret, out var entry) || entry.Value.Authenticated)
+        {
+            return Task.FromResult(false);
+        }
+
+        return Task.FromResult(_authorizationClaims.TryAdd(secret, expiresUtc));
+    }
+
+    /// <inheritdoc />
+    public Task SetAuthorizationAsync(string secret, AuthenticationResult authenticationResult, DateTime expiresUtc, CancellationToken cancellationToken = default)
+    {
+        Expire();
+        _authorizations[secret] = new Entry<AuthenticationResult>(expiresUtc, authenticationResult);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task<AuthenticationResult?> TryConsumeAuthorizationAsync(string secret, CancellationToken cancellationToken = default)
+    {
+        Expire();
+        if (!_authorizations.TryRemove(secret, out var entry) || entry.ExpiresUtc <= DateTime.UtcNow)
+        {
+            return Task.FromResult<AuthenticationResult?>(null);
+        }
+
+        return Task.FromResult<AuthenticationResult?>(entry.Value);
+    }
+
+    private void Expire()
+    {
+        var now = DateTime.UtcNow;
+
+        foreach (var (secret, entry) in _requests)
+        {
+            if (entry.ExpiresUtc <= now)
+            {
+                _requests.TryRemove(secret, out _);
+            }
+        }
+
+        foreach (var (secret, entry) in _authorizations)
+        {
+            if (entry.ExpiresUtc <= now)
+            {
+                _authorizations.TryRemove(secret, out _);
+            }
+        }
+
+        foreach (var (secret, expiresUtc) in _authorizationClaims)
+        {
+            if (expiresUtc <= now)
+            {
+                _authorizationClaims.TryRemove(secret, out _);
+            }
+        }
+    }
+
+    private sealed record Entry<T>(DateTime ExpiresUtc, T Value);
+}

MediaBrowser.Controller/ScheduledTasks/ScanLeaderOptions.cs

@@ -43,6 +43,14 @@ public sealed class ScanLeaderOptions
         "TaskExtractMediaSegments",
         "KeyframeExtraction",
         "CleanupUserDataTask",
-        "OptimizeDatabaseTask"
+        "OptimizeDatabaseTask",
+        "DownloadLyrics",
+        "DownloadSubtitles",
+        "TmdbRefreshUpcomingEpisodes",
+        "RefreshTrickplayImages",
+        "MoveTrickplayImages",
+        "RefreshInternetChannels",
+        "RefreshGuide",
+        "PluginUpdates"
     };
 }

MediaBrowser.Controller/Sorting/IUserBaseItemComparer.cs

@@ -1,6 +1,9 @@
 #nullable disable
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Database.Implementations.Entities;
+using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
 
 namespace MediaBrowser.Controller.Sorting
@@ -27,5 +30,16 @@ namespace MediaBrowser.Controller.Sorting
         /// </summary>
         /// <value>The user data repository.</value>
         IUserDataManager UserDataManager { get; set; }
+
+        /// <summary>
+        /// Gets or sets user data for the items being sorted, keyed by item id, read once up front.
+        /// A comparer that does not store it reads its user data one item at a time instead.
+        /// </summary>
+        /// <value>The prefetched user data, or <c>null</c> when none was prefetched.</value>
+        IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData
+        {
+            get => null;
+            set { }
+        }
     }
 }

MediaBrowser.Controller/Sorting/UserBaseItemComparerExtensions.cs

@@ -0,0 +1,28 @@
+#nullable disable
+
+using MediaBrowser.Controller.Entities;
+
+namespace MediaBrowser.Controller.Sorting
+{
+    /// <summary>
+    /// Helpers shared by the comparers that sort on user data.
+    /// </summary>
+    public static class UserBaseItemComparerExtensions
+    {
+        /// <summary>
+        /// Gets the user data for an item, preferring the batch the sort prefetched.
+        /// </summary>
+        /// <param name="comparer">The comparer.</param>
+        /// <param name="item">The item.</param>
+        /// <returns>The item's user data.</returns>
+        public static UserItemData GetUserData(this IUserBaseItemComparer comparer, BaseItem item)
+        {
+            if (comparer.PrefetchedUserData is not null && comparer.PrefetchedUserData.TryGetValue(item.Id, out var userData))
+            {
+                return userData;
+            }
+
+            return comparer.UserDataManager.GetUserData(comparer.User, item);
+        }
+    }
+}

MediaBrowser.Model/Querying/NextUpQuery.cs

@@ -12,7 +12,7 @@ public class NextUpQuery
     {
         EnableImageTypes = Array.Empty<ImageType>();
         EnableTotalRecordCount = true;
-        NextUpDateCutoff = DateTime.MinValue;
+        NextUpDateCutoff = DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc);
         EnableResumable = false;
         EnableRewatching = false;
     }
@@ -56,7 +56,7 @@ public class NextUpQuery
     public bool EnableTotalRecordCount { get; set; }
 
     /// <summary>
-    /// Gets or sets a value indicating the oldest date for a show to appear in Next Up.
+    /// Gets or sets a value indicating the oldest date, in UTC, for a show to appear in Next Up.
     /// </summary>
     public DateTime NextUpDateCutoff { get; set; }
 

src/Jellyfin.LiveTv/Channels/ChannelManager.cs

@@ -212,7 +212,8 @@ namespace Jellyfin.LiveTv.Channels
             if (query.IsFavorite.HasValue)
             {
                 var val = query.IsFavorite.Value;
-                channels = channels.Where(i => _userDataManager.GetUserData(user, i).IsFavorite == val)
+                var userData = _userDataManager.GetUserDataBatch(channels, user);
+                channels = channels.Where(i => userData.TryGetValue(i.Id, out var data) && data.IsFavorite == val)
                     .ToList();
             }
 

src/Jellyfin.LiveTv/LiveTvManager.cs

@@ -304,8 +304,17 @@ namespace Jellyfin.LiveTv
 
             if (query.IsAiring ?? false)
             {
+                // Scoring reads the channel's user data per program, so read every channel's in one query.
+                var channels = programList
+                    .Cast<LiveTvProgram>()
+                    .Select(i => _libraryManager.GetItemById(i.ChannelId))
+                    .OfType<BaseItem>()
+                    .DistinctBy(i => i.Id)
+                    .ToList();
+                var channelUserData = _userDataManager.GetUserDataBatch(channels, user);
+
                 orderedPrograms = orderedPrograms
-                    .ThenByDescending(i => GetRecommendationScore(i, user, true));
+                    .ThenByDescending(i => GetRecommendationScore(i, user, true, channelUserData));
             }
 
             IEnumerable<BaseItem> programs = orderedPrograms;
@@ -338,7 +347,11 @@ namespace Jellyfin.LiveTv
                 _dtoService.GetBaseItemDtos(internalResult.Items, options, query.User)));
         }
 
-        private int GetRecommendationScore(LiveTvProgram program, User user, bool factorChannelWatchCount)
+        private int GetRecommendationScore(
+            LiveTvProgram program,
+            User user,
+            bool factorChannelWatchCount,
+            IReadOnlyDictionary<Guid, UserItemData> channelUserData)
         {
             var score = 0;
 
@@ -359,7 +372,9 @@ namespace Jellyfin.LiveTv
                 return score;
             }
 
-            var channelUserdata = _userDataManager.GetUserData(user, channel);
+            var channelUserdata = channelUserData.TryGetValue(channel.Id, out var cached)
+                ? cached
+                : _userDataManager.GetUserData(user, channel);
 
             if (channelUserdata.Likes.HasValue)
             {

src/Jellyfin.LiveTv/Recordings/RecordingsManager.cs

@@ -444,6 +444,13 @@ public sealed class RecordingsManager : IRecordingsManager, IDisposable
 
     private async void OnNamedConfigurationUpdated(object? sender, ConfigurationUpdateEventArgs e)
     {
+        // The instance that wrote the change creates the folders; racing it from here would write the
+        // same virtual folder a second time.
+        if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+        {
+            return;
+        }
+
         if (string.Equals(e.Key, "livetv", StringComparison.OrdinalIgnoreCase))
         {
             await CreateRecordingFolders().ConfigureAwait(false);

tests/Jellyfin.Server.Implementations.Tests/Configuration/ApplicationHostPortChangeTests.cs

@@ -0,0 +1,81 @@
+using Emby.Server.Implementations;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// The decision <c>ApplicationHost.OnConfigurationUpdated</c> makes about a port change. The ports this
+/// process bound are fixed for its lifetime and the pending-restart flag is per-process, so an instance
+/// applying another instance's port change still has to notice its own binding went stale - while leaving
+/// the authorization write, and the notice that follows it, to the instance that made the change.
+/// </summary>
+public static class ApplicationHostPortChangeTests
+{
+    /// <summary>
+    /// The local case, unchanged: clear the authorization flag and report the pending restart.
+    /// </summary>
+    [Fact]
+    public static void LocalPortChange_ClearsAuthorizationAndRequiresRestart()
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, true, false);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.True(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// The cross-instance case: the peer wrote the new port and cleared the flag with it, so this
+    /// instance must not write, but it is still listening on the old port and has to say so.
+    /// </summary>
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public static void RemotePortChange_RequiresRestartWithoutWriting(bool isPortAuthorized)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, isPortAuthorized, true);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// A second update while a port change is already pending must not write the flag again, and the
+    /// binding is still stale.
+    /// </summary>
+    [Fact]
+    public static void LocalPortChange_WithAuthorizationAlreadyCleared_RequiresRestartWithoutWriting()
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, false, false);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// An update that leaves the ports alone is not a port change, whoever wrote it.
+    /// </summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public static void UnchangedPorts_DoNothing(bool isApplyingRemoteInvalidation)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 8096, 8920, true, isApplyingRemoteInvalidation);
+
+        Assert.False(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// Nothing is decided before the ports have been bound.
+    /// </summary>
+    [Theory]
+    [InlineData(0, 8920)]
+    [InlineData(8096, 0)]
+    public static void UnboundPorts_DoNothing(int boundHttpPort, int boundHttpsPort)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(boundHttpPort, boundHttpsPort, 9096, 9920, true, false);
+
+        Assert.False(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/FakeInvalidationBusFabric.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using MediaBrowser.Common.Configuration;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// An in-process stand-in for the Redis pub/sub bus: every endpoint connected to one fabric receives
+/// what the others publish, and never its own notices.
+/// </summary>
+internal sealed class FakeInvalidationBusFabric
+{
+    private readonly List<Endpoint> _endpoints = new();
+
+    /// <summary>
+    /// Connects a new instance to the fabric.
+    /// </summary>
+    /// <param name="originId">The identity of the connecting instance.</param>
+    /// <returns>The bus of that instance.</returns>
+    public IConfigurationInvalidationBus Connect(string originId)
+    {
+        var endpoint = new Endpoint(this, originId);
+        lock (_endpoints)
+        {
+            _endpoints.Add(endpoint);
+        }
+
+        return endpoint;
+    }
+
+    private void Broadcast(ConfigurationInvalidation invalidation)
+    {
+        Endpoint[] endpoints;
+        lock (_endpoints)
+        {
+            endpoints = _endpoints.ToArray();
+        }
+
+        foreach (var endpoint in endpoints.Where(e => !string.Equals(e.OriginId, invalidation.OriginId, StringComparison.Ordinal)))
+        {
+            endpoint.Deliver(invalidation);
+        }
+    }
+
+    private sealed class Endpoint : IConfigurationInvalidationBus
+    {
+        private readonly FakeInvalidationBusFabric _fabric;
+        private readonly List<Action<ConfigurationInvalidation>> _handlers = new();
+
+        public Endpoint(FakeInvalidationBusFabric fabric, string originId)
+        {
+            _fabric = fabric;
+            OriginId = originId;
+        }
+
+        public string OriginId { get; }
+
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+            => _fabric.Broadcast(new ConfigurationInvalidation { Scope = scope, Target = target, OriginId = OriginId });
+
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+            => _handlers.Add(handler);
+
+        public void Deliver(ConfigurationInvalidation invalidation)
+        {
+            foreach (var handler in _handlers)
+            {
+                handler(invalidation);
+            }
+        }
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/LibraryVisibilityPropagationTests.cs

@@ -0,0 +1,161 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using Jellyfin.Data;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Enums;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Model.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Library options are cached in a process-wide dictionary, so the replica that did not serve the admin's
+/// request is the one under test here: the other replica's write reaches the shared library directory, and
+/// this one has to stop answering out of its own stale copy.
+/// </summary>
+/// <remarks>
+/// Disabling a library is an access revocation that overrides every per-user check, so a stale replica
+/// keeps serving content that is supposed to be hidden from everyone.
+/// </remarks>
+public sealed class LibraryVisibilityPropagationTests : IDisposable
+{
+    private readonly string _libraryPath;
+    private readonly MyXmlSerializer _serializer = new MyXmlSerializer();
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="LibraryVisibilityPropagationTests"/> class.
+    /// </summary>
+    public LibraryVisibilityPropagationTests()
+    {
+        _libraryPath = Path.Combine(Path.GetTempPath(), "jf-library-prop-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_libraryPath);
+
+        var applicationHost = new Mock<IServerApplicationHost>();
+        applicationHost.Setup(host => host.ExpandVirtualPath(It.IsAny<string>())).Returns<string>(path => path);
+        applicationHost.Setup(host => host.ReverseVirtualPath(It.IsAny<string>())).Returns<string>(path => path);
+
+        CollectionFolder.XmlSerializer = _serializer;
+        CollectionFolder.ApplicationHost = applicationHost.Object;
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        CollectionFolder.InvalidationBus = NullConfigurationInvalidationBus.Instance;
+        CollectionFolder.InvalidateAllLibraryOptions();
+
+        try
+        {
+            Directory.Delete(_libraryPath, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Disabling a library on one replica has to hide it on every replica. Until it does, the ones that did
+    /// not serve the request keep the library visible to every user.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task LibraryDisabledOnAnotherInstance_IsNotVisibleHere()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var otherInstance = fabric.Connect("pod-a");
+        await SubscribeThisInstanceAsync(fabric);
+
+        WriteSharedOptions(enabled: true);
+
+        var user = CreateUser();
+        var library = new CollectionFolder { Path = _libraryPath, Name = "Movies" };
+
+        // This replica answers out of its cache from here on.
+        Assert.True(library.IsVisible(user));
+
+        // The admin disables the library on the other replica: it writes the shared directory and says so.
+        WriteSharedOptions(enabled: false);
+        otherInstance.Publish(ConfigurationInvalidationScope.LibraryOptions, _libraryPath);
+
+        Assert.False(library.IsVisible(user));
+        Assert.False(CollectionFolder.GetLibraryOptions(_libraryPath).Enabled);
+    }
+
+    /// <summary>
+    /// A path remap made on another replica has to reach this one, or it keeps resolving media against a
+    /// path that is no longer the library's.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task LibraryPathRemappedOnAnotherInstance_IsSeenHere()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var otherInstance = fabric.Connect("pod-a");
+        await SubscribeThisInstanceAsync(fabric);
+
+        WriteSharedOptions(enabled: true, mediaPath: "/media/old");
+        Assert.Equal("/media/old", CollectionFolder.GetLibraryOptions(_libraryPath).PathInfos[0].Path);
+
+        WriteSharedOptions(enabled: true, mediaPath: "/media/new");
+        otherInstance.Publish(ConfigurationInvalidationScope.LibraryOptions, _libraryPath);
+
+        Assert.Equal("/media/new", CollectionFolder.GetLibraryOptions(_libraryPath).PathInfos[0].Path);
+    }
+
+    /// <summary>
+    /// Saving library options here has to tell the other replicas, which is the half of the exchange the
+    /// tests above take as given.
+    /// </summary>
+    [Fact]
+    public void SaveLibraryOptions_AnnouncesTheLibraryToTheOtherInstances()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        ConfigurationInvalidation? received = null;
+
+        var otherInstance = fabric.Connect("pod-b");
+        otherInstance.Subscribe(invalidation => received = invalidation);
+        CollectionFolder.InvalidationBus = fabric.Connect("pod-a");
+
+        CollectionFolder.SaveLibraryOptions(_libraryPath, new LibraryOptions { Enabled = false });
+
+        Assert.NotNull(received);
+        Assert.Equal(ConfigurationInvalidationScope.LibraryOptions, received.Scope);
+        Assert.Equal(_libraryPath, received.Target);
+    }
+
+    private async Task SubscribeThisInstanceAsync(FakeInvalidationBusFabric fabric)
+    {
+        var bus = fabric.Connect("pod-b");
+        CollectionFolder.InvalidationBus = bus;
+
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            bus,
+            Mock.Of<IConfigurationManager>(),
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+    }
+
+    private void WriteSharedOptions(bool enabled, string mediaPath = "/media")
+    {
+        // Written the way the other replica writes it, straight onto the shared directory.
+        var options = new LibraryOptions { Enabled = enabled, PathInfos = [new MediaPathInfo(mediaPath)] };
+        _serializer.SerializeToFile(options, Path.Combine(_libraryPath, "options.xml"));
+    }
+
+    private static User CreateUser()
+    {
+        var user = new User("propagation", "auth", "reset");
+        user.SetPermission(PermissionKind.EnableAllFolders, true);
+        return user;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/RedisConfigurationInvalidationBusTests.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Configuration;
+using MediaBrowser.Common.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using StackExchange.Redis;
+using Testcontainers.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Round-trips <see cref="RedisConfigurationInvalidationBus"/> through a real Redis, the transport two
+/// replicas actually use to tell each other that the shared configuration directory has changed.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class RedisConfigurationInvalidationBusTests : IAsyncLifetime
+{
+    private readonly RedisContainer _container;
+    private IConnectionMultiplexer? _redis;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RedisConfigurationInvalidationBusTests"/> class.
+    /// </summary>
+    public RedisConfigurationInvalidationBusTests()
+    {
+        _container = new RedisBuilder("redis:7-alpine").Build();
+    }
+
+    /// <inheritdoc />
+    public async ValueTask InitializeAsync()
+    {
+        await _container.StartAsync();
+        _redis = await ConnectionMultiplexer.ConnectAsync(_container.GetConnectionString());
+    }
+
+    /// <inheritdoc />
+    public async ValueTask DisposeAsync()
+    {
+        if (_redis is not null)
+        {
+            await _redis.DisposeAsync();
+        }
+
+        await _container.DisposeAsync();
+    }
+
+    /// <summary>
+    /// A notice published by one replica reaches the other, carrying enough to invalidate one entry.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Publish_ReachesTheOtherInstance()
+    {
+        var received = new TaskCompletionSource<ConfigurationInvalidation>();
+        var instanceA = CreateBus("pod-a");
+        var instanceB = CreateBus("pod-b");
+
+        instanceB.Subscribe(invalidation => received.TrySetResult(invalidation));
+
+        instanceA.Publish(ConfigurationInvalidationScope.LibraryOptions, "/media/movies");
+
+        var invalidation = await received.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+        Assert.Equal(ConfigurationInvalidationScope.LibraryOptions, invalidation.Scope);
+        Assert.Equal("/media/movies", invalidation.Target);
+        Assert.Equal("pod-a", invalidation.OriginId);
+    }
+
+    /// <summary>
+    /// The publishing replica has already applied the change to its own cache, so it must not act on its
+    /// own notice and reload what it just wrote.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Publish_IsNotDeliveredToThePublisher()
+    {
+        var ownNotice = new TaskCompletionSource<ConfigurationInvalidation>();
+        var otherNotice = new TaskCompletionSource<ConfigurationInvalidation>();
+        var instanceA = CreateBus("pod-a");
+        var instanceB = CreateBus("pod-b");
+
+        instanceA.Subscribe(invalidation => ownNotice.TrySetResult(invalidation));
+        instanceB.Subscribe(invalidation => otherNotice.TrySetResult(invalidation));
+
+        instanceA.Publish(ConfigurationInvalidationScope.SystemConfiguration, null);
+
+        // Ordering is per channel, so B having the notice means A would have had it too.
+        await otherNotice.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+        Assert.False(ownNotice.Task.IsCompleted);
+    }
+
+    private RedisConfigurationInvalidationBus CreateBus(string originId)
+    {
+        Environment.SetEnvironmentVariable("JELLYFIN_INSTANCE_ID", originId);
+        try
+        {
+            return new RedisConfigurationInvalidationBus(_redis!, NullLogger<RedisConfigurationInvalidationBus>.Instance);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("JELLYFIN_INSTANCE_ID", null);
+        }
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/RemoteInvalidationApplyTests.cs

@@ -0,0 +1,205 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Net;
+using MediaBrowser.Controller.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Applying an invalidation re-raises the same update events a local save raises, and some consumers of
+/// those events answer an update by writing - <c>RecordingsManager</c> creating the recording folders for
+/// the <c>livetv</c> key, <c>ApplicationHost</c> clearing <c>IsPortAuthorized</c> on a port change. The
+/// instance that did not write must not repeat those writes, and no write it is induced into must reach
+/// the bus.
+/// </summary>
+public sealed class RemoteInvalidationApplyTests : IDisposable
+{
+    private readonly string _root;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RemoteInvalidationApplyTests"/> class.
+    /// </summary>
+    public RemoteInvalidationApplyTests()
+    {
+        _root = Path.Combine(Path.GetTempPath(), "jf-config-apply-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_root);
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        try
+        {
+            Directory.Delete(_root, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// A consumer that knows nothing about the bus - a plugin, or anything reached transitively from one -
+    /// can answer an applied invalidation by writing. That write must not become a notice of its own.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedInvalidation_InducingAWriteOnTheReceiver_DoesNotPublishBack()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var writesByB = 0;
+        instanceB.NamedConfigurationUpdated += (_, e) =>
+        {
+            // One shot: the induced write raises the event again on this instance.
+            if (Interlocked.Increment(ref writesByB) > 1)
+            {
+                return;
+            }
+
+            var configuration = (NetworkConfiguration)instanceB.GetConfiguration(e.Key);
+            configuration.PublishedServerUriBySubnet = ["10.0.0.0/8=example"];
+            instanceB.SaveConfiguration(e.Key, configuration);
+        };
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(0, receivedByA);
+
+        // The point of the bus still holds: B is not left on its stale copy.
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+    }
+
+    /// <summary>
+    /// The shape of <c>RecordingsManager</c>: a consumer that answers a named configuration update by
+    /// writing has to be able to tell that the write was another instance's, and skip it.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedInvalidation_WithAWriteTriggeringConsumer_DoesNotDuplicateTheWrite()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var writesByB = 0;
+        instanceB.NamedConfigurationUpdated += (_, e) =>
+        {
+            if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+            {
+                return;
+            }
+
+            Interlocked.Increment(ref writesByB);
+        };
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(0, writesByB);
+        Assert.Equal(0, receivedByA);
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+
+        // A read-only consumer is still told, which is what the invalidation exists for.
+        var refreshes = 0;
+        instanceB.NamedConfigurationUpdated += (_, _) => Interlocked.Increment(ref refreshes);
+
+        updated.EnableRemoteAccess = true;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(1, refreshes);
+    }
+
+    /// <summary>
+    /// The <c>ApplicationHost.IsPortAuthorized</c> class of consumer: the system configuration event is
+    /// queued rather than raised inline, so the fix has to survive the hop onto the thread pool.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task SystemInvalidation_InducingAQueuedWriteOnTheReceiver_DoesNotPublishBack()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var applied = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var handled = 0;
+        instanceB.ConfigurationUpdated += (_, _) =>
+        {
+            if (Interlocked.Increment(ref handled) > 1)
+            {
+                return;
+            }
+
+            instanceB.Configuration.IsPortAuthorized = false;
+            instanceB.SaveConfiguration();
+            applied.TrySetResult();
+        };
+
+        instanceA.Configuration.QuickConnectAvailable = false;
+        instanceA.SaveConfiguration();
+
+        await applied.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+
+        Assert.Equal(0, receivedByA);
+        Assert.False(instanceB.Configuration.QuickConnectAvailable);
+    }
+
+    private async Task<ServerConfigurationManager> CreateSubscribedInstanceAsync(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var instance = CreateInstance(fabric, originId);
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            instance.InvalidationBus,
+            instance,
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+        return instance;
+    }
+
+    private ServerConfigurationManager CreateInstance(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var paths = new ServerApplicationPaths(
+            Ensure("data"),
+            Ensure("log"),
+            Ensure("config"),
+            Ensure("cache"),
+            Ensure("web"));
+
+        var manager = new ServerConfigurationManager(paths, NullLoggerFactory.Instance, new MyXmlSerializer())
+        {
+            InvalidationBus = fabric.Connect(originId)
+        };
+
+        manager.AddParts([new NetworkConfigurationFactory()]);
+        return manager;
+    }
+
+    private string Ensure(string name)
+    {
+        var path = Path.Combine(_root, name);
+        Directory.CreateDirectory(path);
+        return path;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/SharedConfigurationPropagationTests.cs

@@ -0,0 +1,147 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Net;
+using MediaBrowser.Controller.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using StackExchange.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Two independently constructed <see cref="ServerConfigurationManager"/> instances over one configuration
+/// directory are the in-process stand-in for two replicas sharing one <c>/config</c> mount: what either of
+/// them writes, the other has to pick up without being restarted.
+/// </summary>
+public sealed class SharedConfigurationPropagationTests : IDisposable
+{
+    private readonly string _root;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SharedConfigurationPropagationTests"/> class.
+    /// </summary>
+    public SharedConfigurationPropagationTests()
+    {
+        _root = Path.Combine(Path.GetTempPath(), "jf-config-prop-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_root);
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        try
+        {
+            Directory.Delete(_root, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// A system configuration setting tightened on one replica has to hold on every other replica, not
+    /// only on the one that served the admin's request.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task SystemConfigurationSavedOnOneInstance_IsSeenByAnotherWithoutRestart()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        // B has the pre-change configuration in hand before A writes, as a running replica would.
+        Assert.True(instanceB.Configuration.QuickConnectAvailable);
+
+        instanceA.Configuration.QuickConnectAvailable = false;
+        instanceA.SaveConfiguration();
+
+        Assert.False(instanceB.Configuration.QuickConnectAvailable);
+    }
+
+    /// <summary>
+    /// The same has to hold for the named configurations, which are cached per key and never reloaded.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedConfigurationSavedOnOneInstance_IsSeenByAnotherWithoutRestart()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        Assert.True(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+    }
+
+    /// <summary>
+    /// A replica that cannot reach the bus keeps serving: the admin's save still lands on the shared
+    /// directory, and the only loss is that the other replicas are not told about it.
+    /// </summary>
+    [Fact]
+    public void SaveConfiguration_WithUnreachableBus_DoesNotThrow()
+    {
+        using var multiplexer = ConnectionMultiplexer.Connect("127.0.0.1:1,abortConnect=false,connectTimeout=200,connectRetry=1,syncTimeout=200");
+        var bus = new RedisConfigurationInvalidationBus(multiplexer, NullLogger<RedisConfigurationInvalidationBus>.Instance);
+
+        bus.Subscribe(_ => throw new InvalidOperationException("Nothing can be delivered by an unreachable bus."));
+
+        var instance = CreateInstance(new FakeInvalidationBusFabric(), "pod-a");
+        instance.InvalidationBus = bus;
+
+        instance.Configuration.QuickConnectAvailable = false;
+        instance.SaveConfiguration();
+        instance.SaveConfiguration(NetworkConfigurationStore.StoreKey, instance.GetNetworkConfiguration());
+
+        Assert.False(instance.Configuration.QuickConnectAvailable);
+    }
+
+    private async Task<ServerConfigurationManager> CreateSubscribedInstanceAsync(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var instance = CreateInstance(fabric, originId);
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            instance.InvalidationBus,
+            instance,
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+        return instance;
+    }
+
+    private ServerConfigurationManager CreateInstance(FakeInvalidationBusFabric fabric, string originId)
+    {
+        // Every instance has its own paths object, all of them pointing at the one shared directory.
+        var paths = new ServerApplicationPaths(
+            Ensure("data"),
+            Ensure("log"),
+            Ensure("config"),
+            Ensure("cache"),
+            Ensure("web"));
+
+        var manager = new ServerConfigurationManager(paths, NullLoggerFactory.Instance, new MyXmlSerializer())
+        {
+            InvalidationBus = fabric.Connect(originId)
+        };
+
+        manager.AddParts([new NetworkConfigurationFactory()]);
+        return manager;
+    }
+
+    private string Ensure(string name)
+    {
+        var path = Path.Combine(_root, name);
+        Directory.CreateDirectory(path);
+        return path;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Jellyfin.Server.Implementations.Tests.csproj

@@ -31,6 +31,8 @@
   <ItemGroup>
     <ProjectReference Include="..\..\Emby.Server.Implementations\Emby.Server.Implementations.csproj" />
     <ProjectReference Include="..\..\Jellyfin.Server.Implementations\Jellyfin.Server.Implementations.csproj" />
+    <ProjectReference Include="..\..\MediaBrowser.Providers\MediaBrowser.Providers.csproj" />
+    <ProjectReference Include="..\..\src\Jellyfin.LiveTv\Jellyfin.LiveTv.csproj" />
     <ProjectReference Include="..\Jellyfin.Server.Integration.Tests\Jellyfin.Server.Integration.Tests.csproj" />
     <ProjectReference Include="..\..\src\Jellyfin.Database\Jellyfin.Database.Implementations\Jellyfin.Database.Implementations.csproj" />
   </ItemGroup>

tests/Jellyfin.Server.Implementations.Tests/Library/LibraryManagerSortTests.cs

@@ -7,6 +7,7 @@ using Emby.Naming.Common;
 using Emby.Server.Implementations.Library;
 using Emby.Server.Implementations.Sorting;
 using Jellyfin.Data.Enums;
+using Jellyfin.Database.Implementations.Entities;
 using Jellyfin.Database.Implementations.Enums;
 using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Entities;
@@ -63,13 +64,49 @@ public class LibraryManagerSortTests
         Assert.Equal(new[] { "Alpha", "Mike", "Zulu" }, sorted.Select(i => i.Name));
     }
 
+    [Fact]
+    public void Sort_ComparerThatIgnoresPrefetchedUserData_StillSortsFromLiveReads()
+    {
+        var alpha = new Audio { Name = "Alpha", SortName = "Alpha", Id = Guid.NewGuid() };
+        var zulu = new Audio { Name = "Zulu", SortName = "Zulu", Id = Guid.NewGuid() };
+        var playCounts = new Dictionary<Guid, int> { [alpha.Id] = 1, [zulu.Id] = 9 };
+
+        var userDataManager = new Mock<IUserDataManager>();
+        userDataManager
+            .Setup(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()))
+            .Returns<User, BaseItem>((_, item) => new UserItemData { Key = item.Id.ToString("N"), PlayCount = playCounts[item.Id] });
+        userDataManager
+            .Setup(u => u.GetUserDataBatch(It.IsAny<IReadOnlyList<BaseItem>>(), It.IsAny<User>()))
+            .Returns(new Dictionary<Guid, UserItemData>());
+
+        var libraryManager = CreateLibraryManager(
+            new IBaseItemComparer[] { new PluginPlayCountComparer() },
+            userDataManager);
+
+        var sorted = libraryManager.Sort(
+            new BaseItem[] { alpha, zulu },
+            new User("sorter", "provider", "provider"),
+            new[] { (ItemSortBy.PlayCount, SortOrder.Descending) }).ToArray();
+
+        Assert.Equal(new[] { "Zulu", "Alpha" }, sorted.Select(i => i.Name));
+        userDataManager.Verify(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()), Times.AtLeastOnce);
+    }
+
     private static Folder MakeFolder(string name, DateTime dateLastMediaAdded)
         => new() { Name = name, Id = Guid.NewGuid(), DateLastMediaAdded = dateLastMediaAdded };
 
-    private static Emby.Server.Implementations.Library.LibraryManager CreateLibraryManager(IReadOnlyCollection<IBaseItemComparer> comparers)
+    private static Emby.Server.Implementations.Library.LibraryManager CreateLibraryManager(
+        IReadOnlyCollection<IBaseItemComparer> comparers,
+        Mock<IUserDataManager>? userDataManager = null)
     {
         var fixture = new Fixture().Customize(new AutoMoqCustomization());
         fixture.Register(() => new NamingOptions());
+
+        if (userDataManager is not null)
+        {
+            fixture.Inject(userDataManager.Object);
+        }
+
         var configMock = fixture.Freeze<Mock<IServerConfigurationManager>>();
         configMock.Setup(c => c.ApplicationPaths.ProgramDataPath).Returns("/data");
         BaseItem.ConfigurationManager ??= configMock.Object;
@@ -86,4 +123,22 @@ public class LibraryManagerSortTests
                 fixture.Create<IEnumerable<ILibraryPostScanTask>>()))
             .Create();
     }
+
+    /// <summary>
+    /// A comparer of the shape a third-party plugin ships: it implements
+    /// <see cref="IUserBaseItemComparer"/> without ever mentioning PrefetchedUserData.
+    /// </summary>
+    public sealed class PluginPlayCountComparer : IUserBaseItemComparer
+    {
+        public User User { get; set; } = null!;
+
+        public IUserManager UserManager { get; set; } = null!;
+
+        public IUserDataManager UserDataManager { get; set; } = null!;
+
+        public ItemSortBy Type => ItemSortBy.PlayCount;
+
+        public int Compare(BaseItem? x, BaseItem? y)
+            => UserDataManager.GetUserData(User, x!)!.PlayCount.CompareTo(UserDataManager.GetUserData(User, y!)!.PlayCount);
+    }
 }

tests/Jellyfin.Server.Implementations.Tests/Library/UserDataManagerTests.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using Emby.Server.Implementations.Library;
 using Jellyfin.Database.Implementations;
 using Jellyfin.Database.Implementations.Entities;
@@ -49,6 +48,12 @@ public sealed class UserDataManagerTests : IDisposable
         {
             Id = Guid.NewGuid()
         };
+
+        using (var ctx = CreateDbContext())
+        {
+            ctx.Users.Add(_user);
+            ctx.SaveChanges();
+        }
     }
 
     public void Dispose()
@@ -78,6 +83,23 @@ public sealed class UserDataManagerTests : IDisposable
         };
     }
 
+    private void Seed(AudioBook item, params UserData[] rows)
+    {
+        using var ctx = CreateDbContext();
+        ctx.BaseItems.Add(new BaseItemEntity { Id = item.Id, Type = typeof(AudioBook).FullName! });
+        ctx.UserData.AddRange(rows);
+        ctx.SaveChanges();
+    }
+
+    private User CreateOtherUser()
+    {
+        var user = new User("other", "auth-provider", "reset-provider") { Id = Guid.NewGuid() };
+        using var ctx = CreateDbContext();
+        ctx.Users.Add(user);
+        ctx.SaveChanges();
+        return user;
+    }
+
     private UserData CreateUserDataRow(AudioBook item, string key, long positionTicks)
     {
         return new UserData
@@ -98,11 +120,10 @@ public sealed class UserDataManagerTests : IDisposable
         var currentKey = item.GetUserDataKeys()[0];
 
         // the retired-key row comes first to ensure selection is by key, not row order
-        item.UserData = new List<UserData>
-        {
+        Seed(
+            item,
             CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111),
-            CreateUserDataRow(item, currentKey, 222)
-        };
+            CreateUserDataRow(item, currentKey, 222));
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -117,11 +138,10 @@ public sealed class UserDataManagerTests : IDisposable
         var item = CreateAudioBook();
         var idKey = item.GetUserDataKeys()[1];
 
-        item.UserData = new List<UserData>
-        {
+        Seed(
+            item,
             CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111),
-            CreateUserDataRow(item, idKey, 333)
-        };
+            CreateUserDataRow(item, idKey, 333));
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -135,10 +155,7 @@ public sealed class UserDataManagerTests : IDisposable
     {
         var item = CreateAudioBook();
 
-        item.UserData = new List<UserData>
-        {
-            CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111)
-        };
+        Seed(item, CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111));
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -150,7 +167,7 @@ public sealed class UserDataManagerTests : IDisposable
     public void GetUserData_NoRows_ReturnsDefaultWithPrimaryKey()
     {
         var item = CreateAudioBook();
-        item.UserData = new List<UserData>();
+        Seed(item);
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -166,13 +183,9 @@ public sealed class UserDataManagerTests : IDisposable
         var currentKey = item.GetUserDataKeys()[0];
 
         var otherUserRow = CreateUserDataRow(item, currentKey, 999);
-        otherUserRow.UserId = Guid.NewGuid();
+        otherUserRow.UserId = CreateOtherUser().Id;
 
-        item.UserData = new List<UserData>
-        {
-            otherUserRow,
-            CreateUserDataRow(item, currentKey, 222)
-        };
+        Seed(item, otherUserRow, CreateUserDataRow(item, currentKey, 222));
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -183,23 +196,15 @@ public sealed class UserDataManagerTests : IDisposable
     [Fact]
     public void GetUserDataBatch_DatabaseFallback_ResolvesRowsByKeyOrder()
     {
-        // no preloaded navigation data, so the batch takes the database fallback
         var fossilItem = CreateAudioBook();
         var retiredItem = CreateAudioBook();
 
-        using (var ctx = CreateDbContext())
-        {
-            ctx.Users.Add(_user);
-            ctx.BaseItems.Add(new BaseItemEntity { Id = fossilItem.Id, Type = typeof(AudioBook).FullName! });
-            ctx.BaseItems.Add(new BaseItemEntity { Id = retiredItem.Id, Type = typeof(AudioBook).FullName! });
-
-            // the stale id-key row is inserted first so selection by row order would return it
-            ctx.UserData.AddRange(
-                CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[1], 111),
-                CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[0], 222),
-                CreateUserDataRow(retiredItem, "Author-Old Album-0001Old File Name", 333));
-            ctx.SaveChanges();
-        }
+        // the stale id-key row is inserted first so selection by row order would return it
+        Seed(
+            fossilItem,
+            CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[1], 111),
+            CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[0], 222));
+        Seed(retiredItem, CreateUserDataRow(retiredItem, "Author-Old Album-0001Old File Name", 333));
 
         var result = _userDataManager.GetUserDataBatch([fossilItem, retiredItem], _user);
 

tests/Jellyfin.Server.Implementations.Tests/QuickConnect/QuickConnectManagerTests.cs

@@ -8,6 +8,7 @@ using MediaBrowser.Common.Extensions;
 using MediaBrowser.Controller.Authentication;
 using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Net;
+using MediaBrowser.Controller.QuickConnect;
 using MediaBrowser.Model.Configuration;
 using Moq;
 using Xunit;
@@ -40,6 +41,8 @@ namespace Jellyfin.Server.Implementations.Tests.QuickConnect
                 ConfigureMembers = true
             }).Inject(configManager.Object);
 
+            _fixture.Inject<IQuickConnectStore>(new InMemoryQuickConnectStore());
+
             // User object contains circular references.
             _fixture.Behaviors.OfType<ThrowingRecursionBehavior>().ToList()
                 .ForEach(b => _fixture.Behaviors.Remove(b));
@@ -60,8 +63,8 @@ namespace Jellyfin.Server.Implementations.Tests.QuickConnect
         [InlineData("Device", "", "Client", "1.0.0")]
         [InlineData("Device", "DeviceId", "", "1.0.0")]
         [InlineData("Device", "DeviceId", "Client", "")]
-        public void TryConnect_InvalidAuthorizationInfo_ThrowsArgumentException(string device, string deviceId, string client, string version)
-            => Assert.Throws<ArgumentException>(() => _quickConnectManager.TryConnect(
+        public async Task TryConnect_InvalidAuthorizationInfo_ThrowsArgumentException(string device, string deviceId, string client, string version)
+            => await Assert.ThrowsAsync<ArgumentException>(() => _quickConnectManager.TryConnect(
                 new AuthorizationInfo
                 {
                     Device = device,
@@ -71,17 +74,17 @@ namespace Jellyfin.Server.Implementations.Tests.QuickConnect
                 }));
 
         [Fact]
-        public void TryConnect_QuickConnectUnavailable_ThrowsAuthenticationException()
+        public async Task TryConnect_QuickConnectUnavailable_ThrowsAuthenticationException()
         {
             _config.QuickConnectAvailable = false;
-            Assert.Throws<AuthenticationException>(() => _quickConnectManager.TryConnect(_quickConnectAuthInfo));
+            await Assert.ThrowsAsync<AuthenticationException>(() => _quickConnectManager.TryConnect(_quickConnectAuthInfo));
         }
 
         [Fact]
-        public void CheckRequestStatus_QuickConnectUnavailable_ThrowsAuthenticationException()
+        public async Task CheckRequestStatus_QuickConnectUnavailable_ThrowsAuthenticationException()
         {
             _config.QuickConnectAvailable = false;
-            Assert.Throws<AuthenticationException>(() => _quickConnectManager.CheckRequestStatus(string.Empty));
+            await Assert.ThrowsAsync<AuthenticationException>(() => _quickConnectManager.CheckRequestStatus(string.Empty));
         }
 
         [Fact]
@@ -92,10 +95,10 @@ namespace Jellyfin.Server.Implementations.Tests.QuickConnect
         }
 
         [Fact]
-        public void GetAuthorizedRequest_QuickConnectUnavailable_ThrowsAuthenticationException()
+        public async Task GetAuthorizedRequest_QuickConnectUnavailable_ThrowsAuthenticationException()
         {
             _config.QuickConnectAvailable = false;
-            Assert.Throws<AuthenticationException>(() => _quickConnectManager.GetAuthorizedRequest(string.Empty));
+            await Assert.ThrowsAsync<AuthenticationException>(() => _quickConnectManager.GetAuthorizedRequest(string.Empty));
         }
 
         [Fact]
@@ -106,34 +109,71 @@ namespace Jellyfin.Server.Implementations.Tests.QuickConnect
         }
 
         [Fact]
-        public void CheckRequestStatus_QuickConnectAvailable_Success()
+        public async Task CheckRequestStatus_QuickConnectAvailable_Success()
         {
             _config.QuickConnectAvailable = true;
-            var res1 = _quickConnectManager.TryConnect(_quickConnectAuthInfo);
-            var res2 = _quickConnectManager.CheckRequestStatus(res1.Secret);
-            Assert.Equal(res1, res2);
+            var res1 = await _quickConnectManager.TryConnect(_quickConnectAuthInfo);
+            var res2 = await _quickConnectManager.CheckRequestStatus(res1.Secret);
+            Assert.Equal(res1.Secret, res2.Secret);
+            Assert.Equal(res1.Code, res2.Code);
         }
 
         [Fact]
-        public void CheckRequestStatus_UnknownSecret_ThrowsResourceNotFoundException()
+        public async Task CheckRequestStatus_UnknownSecret_ThrowsResourceNotFoundException()
         {
             _config.QuickConnectAvailable = true;
-            Assert.Throws<ResourceNotFoundException>(() => _quickConnectManager.CheckRequestStatus("Unknown secret"));
+            await Assert.ThrowsAsync<ResourceNotFoundException>(() => _quickConnectManager.CheckRequestStatus("Unknown secret"));
         }
 
         [Fact]
-        public void GetAuthorizedRequest_UnknownSecret_ThrowsResourceNotFoundException()
+        public async Task GetAuthorizedRequest_UnknownSecret_ThrowsResourceNotFoundException()
         {
             _config.QuickConnectAvailable = true;
-            Assert.Throws<ResourceNotFoundException>(() => _quickConnectManager.GetAuthorizedRequest("Unknown secret"));
+            await Assert.ThrowsAsync<ResourceNotFoundException>(() => _quickConnectManager.GetAuthorizedRequest("Unknown secret"));
         }
 
         [Fact]
         public async Task AuthorizeRequest_QuickConnectAvailable_Success()
         {
             _config.QuickConnectAvailable = true;
-            var res = _quickConnectManager.TryConnect(_quickConnectAuthInfo);
+            var res = await _quickConnectManager.TryConnect(_quickConnectAuthInfo);
             Assert.True(await _quickConnectManager.AuthorizeRequest(Guid.Empty, res.Code));
         }
+
+        [Fact]
+        public async Task AuthorizeRequest_RacedOnOneCode_SucceedsOnce()
+        {
+            _config.QuickConnectAvailable = true;
+            var res = await _quickConnectManager.TryConnect(_quickConnectAuthInfo);
+
+            var outcomes = await Task.WhenAll(
+                Task.Run(() => AuthorizeAsync(res.Code)),
+                Task.Run(() => AuthorizeAsync(res.Code)));
+
+            Assert.Single(outcomes, authorized => authorized);
+        }
+
+        [Fact]
+        public async Task GetAuthorizedRequest_SecondExchange_ThrowsResourceNotFoundException()
+        {
+            _config.QuickConnectAvailable = true;
+            var res = await _quickConnectManager.TryConnect(_quickConnectAuthInfo);
+            await _quickConnectManager.AuthorizeRequest(Guid.Empty, res.Code);
+
+            Assert.NotNull(await _quickConnectManager.GetAuthorizedRequest(res.Secret));
+            await Assert.ThrowsAsync<ResourceNotFoundException>(() => _quickConnectManager.GetAuthorizedRequest(res.Secret));
+        }
+
+        private async Task<bool> AuthorizeAsync(string code)
+        {
+            try
+            {
+                return await _quickConnectManager.AuthorizeRequest(Guid.Empty, code).ConfigureAwait(false);
+            }
+            catch (InvalidOperationException)
+            {
+                return false;
+            }
+        }
     }
 }

tests/Jellyfin.Server.Implementations.Tests/ScheduledTasks/ScanLeaderOptionsTests.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Runtime.CompilerServices;
 using Emby.Server.Implementations.ScheduledTasks.Tasks;
 using MediaBrowser.Controller.ScheduledTasks;
@@ -11,6 +13,14 @@ namespace Jellyfin.Server.Implementations.Tests.ScheduledTasks;
 
 public class ScanLeaderOptionsTests
 {
+    private static readonly Assembly[] _taskAssemblies =
+    {
+        typeof(DeleteTranscodeFileTask).Assembly,
+        typeof(MediaBrowser.Providers.Lyric.LyricScheduledTask).Assembly,
+        typeof(Jellyfin.LiveTv.Guide.RefreshGuideScheduledTask).Assembly,
+        typeof(Jellyfin.MediaEncoding.Hls.ScheduledTasks.KeyframeExtractionScheduledTask).Assembly
+    };
+
     /// <summary>
     /// A gated key that matches no registered task silently stops gating anything, so the default
     /// set is pinned to the task keys that actually exist in the build.
@@ -18,28 +28,92 @@ public class ScanLeaderOptionsTests
     [Fact]
     public void DefaultGatedTaskKeys_Should_MatchRegisteredScheduledTasks()
     {
-        var registeredKeys = DiscoverScheduledTaskKeys();
+        var registeredKeys = DiscoverScheduledTaskKeys(_taskAssemblies);
 
         Assert.NotEmpty(registeredKeys);
-        Assert.Empty(new ScanLeaderOptions().GatedTaskKeys.Except(registeredKeys, StringComparer.Ordinal));
+
+        var unmatched = new ScanLeaderOptions().GatedTaskKeys.Except(registeredKeys, StringComparer.Ordinal).ToList();
+        Assert.True(
+            unmatched.Count == 0,
+            $"Gated keys match no scheduled task: {string.Join(", ", unmatched)}. Known keys: {string.Join(", ", registeredKeys.Order(StringComparer.Ordinal))}");
     }
 
-    private static HashSet<string> DiscoverScheduledTaskKeys()
+    /// <summary>
+    /// A key dropped from the default set silently un-gates that task on every replica, so the whole
+    /// set is pinned against a hand-maintained expectation rather than read back from the options.
+    /// </summary>
+    [Fact]
+    public void DefaultGatedTaskKeys_Should_BeTheExpectedSet()
     {
-        var keys = new HashSet<string>(StringComparer.Ordinal);
-        var assemblies = new[]
+        string[] expected =
         {
-            typeof(DeleteTranscodeFileTask).Assembly,
-            typeof(Jellyfin.MediaEncoding.Hls.ScheduledTasks.KeyframeExtractionScheduledTask).Assembly
+            "AudioNormalization",
+            "CleanupUserDataTask",
+            "DownloadLyrics",
+            "DownloadSubtitles",
+            "KeyframeExtraction",
+            "MoveTrickplayImages",
+            "OptimizeDatabaseTask",
+            "PluginUpdates",
+            "RefreshChapterImages",
+            "RefreshGuide",
+            "RefreshInternetChannels",
+            "RefreshLibrary",
+            "RefreshPeople",
+            "RefreshTrickplayImages",
+            "TaskExtractMediaSegments",
+            "TmdbRefreshUpcomingEpisodes"
         };
 
-        foreach (var type in assemblies.SelectMany(a => a.GetTypes()))
+        var actual = new ScanLeaderOptions().GatedTaskKeys;
+        var missing = expected.Except(actual, StringComparer.Ordinal).ToList();
+        var unexpected = actual.Except(expected, StringComparer.Ordinal).ToList();
+
+        Assert.True(
+            missing.Count == 0 && unexpected.Count == 0,
+            $"Default gated task keys drifted. Missing: {Describe(missing)}. Unexpected: {Describe(unexpected)}.");
+    }
+
+    /// <summary>
+    /// The key universe is only as complete as the assemblies it is read from, so a task added to an
+    /// unscanned assembly must fail here rather than narrow what the previous test can catch.
+    /// </summary>
+    [Fact]
+    public void TaskAssemblies_Should_CoverEveryAssemblyDeclaringScheduledTasks()
+    {
+        var scanned = _taskAssemblies.Select(a => a.GetName().Name).ToHashSet(StringComparer.Ordinal);
+        var missing = new List<string>();
+
+        foreach (var path in Directory.EnumerateFiles(AppContext.BaseDirectory, "*.dll"))
         {
-            if (type.IsAbstract || type.IsInterface || !typeof(IScheduledTask).IsAssignableFrom(type))
+            var name = Path.GetFileNameWithoutExtension(path);
+            if (scanned.Contains(name)
+                || name.EndsWith(".Tests", StringComparison.Ordinal)
+                || !(name.StartsWith("Jellyfin.", StringComparison.Ordinal)
+                    || name.StartsWith("Emby.", StringComparison.Ordinal)
+                    || name.StartsWith("MediaBrowser.", StringComparison.Ordinal)))
             {
                 continue;
             }
 
+            if (GetScheduledTaskTypes(Assembly.LoadFrom(path)).Any())
+            {
+                missing.Add(name);
+            }
+        }
+
+        Assert.True(missing.Count == 0, $"Assemblies declaring scheduled tasks but not scanned: {string.Join(", ", missing)}");
+    }
+
+    private static string Describe(IReadOnlyCollection<string> keys)
+        => keys.Count == 0 ? "none" : string.Join(", ", keys.Order(StringComparer.Ordinal));
+
+    private static HashSet<string> DiscoverScheduledTaskKeys(IEnumerable<Assembly> assemblies)
+    {
+        var keys = new HashSet<string>(StringComparer.Ordinal);
+
+        foreach (var type in assemblies.SelectMany(GetScheduledTaskTypes))
+        {
             // Task keys are constant expressions, so an uninitialised instance is enough to read
             // them without standing up each task's dependency graph.
             var task = (IScheduledTask)RuntimeHelpers.GetUninitializedObject(type);
@@ -48,4 +122,21 @@ public class ScanLeaderOptionsTests
 
         return keys;
     }
+
+    private static IEnumerable<Type> GetScheduledTaskTypes(Assembly assembly)
+    {
+        Type?[] types;
+        try
+        {
+            types = assembly.GetTypes();
+        }
+        catch (ReflectionTypeLoadException ex)
+        {
+            types = ex.Types;
+        }
+
+        return types
+            .Where(t => t is not null && !t.IsAbstract && !t.IsInterface && typeof(IScheduledTask).IsAssignableFrom(t))
+            .Select(t => t!);
+    }
 }

tests/Jellyfin.Server.Implementations.Tests/TV/TVSeriesManagerNextUpTests.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using Emby.Server.Implementations.TV;
+using Jellyfin.Database.Implementations.Entities;
+using MediaBrowser.Controller.Configuration;
+using MediaBrowser.Controller.Dto;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Entities.TV;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Controller.Persistence;
+using MediaBrowser.Model.Configuration;
+using MediaBrowser.Model.Querying;
+using Moq;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.TV;
+
+public class TVSeriesManagerNextUpTests
+{
+    [Theory]
+    [InlineData(1)]
+    [InlineData(25)]
+    [InlineData(200)]
+    public void GetNextUp_ReadsUserDataInABoundedNumberOfQueries(int seriesCount)
+    {
+        var user = new User("next-up", "provider", "provider");
+        var libraryManager = new Mock<ILibraryManager>();
+        var userDataManager = new Mock<IUserDataManager>();
+
+        var seriesKeys = Enumerable.Range(0, seriesCount)
+            .Select(i => i.ToString(CultureInfo.InvariantCulture))
+            .ToList();
+
+        var batch = seriesKeys.ToDictionary(
+            key => key,
+            key => new NextUpEpisodeBatchResult
+            {
+                NextUp = new Episode { Id = Guid.NewGuid(), Name = "Next " + key },
+                LastWatched = new Episode { Id = Guid.NewGuid(), Name = "Watched " + key }
+            });
+
+        libraryManager
+            .Setup(l => l.GetNextUpSeriesKeys(It.IsAny<InternalItemsQuery>(), It.IsAny<IReadOnlyCollection<BaseItem>>(), It.IsAny<DateTime>()))
+            .Returns(seriesKeys);
+        libraryManager
+            .Setup(l => l.GetNextUpEpisodesBatch(It.IsAny<InternalItemsQuery>(), It.IsAny<IReadOnlyList<string>>(), It.IsAny<bool>(), It.IsAny<bool>()))
+            .Returns(batch);
+        libraryManager.Setup(l => l.GetLinkedAlternateVersions(It.IsAny<Video>())).Returns([]);
+        libraryManager.Setup(l => l.GetLocalAlternateVersionIds(It.IsAny<Video>())).Returns([]);
+
+        var batchReads = 0;
+        userDataManager
+            .Setup(u => u.GetUserDataBatch(It.IsAny<IReadOnlyList<BaseItem>>(), It.IsAny<User>()))
+            .Returns<IReadOnlyList<BaseItem>, User>((items, _) =>
+            {
+                batchReads++;
+                return items.DistinctBy(i => i.Id).ToDictionary(
+                    i => i.Id,
+                    i => new UserItemData { Key = i.Id.ToString("N", CultureInfo.InvariantCulture) });
+            });
+
+        var previousLibraryManager = BaseItem.LibraryManager;
+        BaseItem.LibraryManager = libraryManager.Object;
+
+        try
+        {
+            var manager = new TVSeriesManager(userDataManager.Object, libraryManager.Object, CreateConfigurationManager());
+
+            var result = manager.GetNextUp(
+                new NextUpQuery { User = user, EnableTotalRecordCount = true },
+                [],
+                new DtoOptions(false));
+
+            Assert.Equal(seriesCount, result.TotalRecordCount);
+
+            // Selection, the resume check and the last played date: three reads whatever the library holds.
+            Assert.Equal(3, batchReads);
+            userDataManager.Verify(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()), Times.Never);
+        }
+        finally
+        {
+            BaseItem.LibraryManager = previousLibraryManager;
+        }
+    }
+
+    private static IServerConfigurationManager CreateConfigurationManager()
+    {
+        var configurationManager = new Mock<IServerConfigurationManager>();
+        configurationManager.SetupGet(c => c.Configuration).Returns(new ServerConfiguration());
+        return configurationManager.Object;
+    }
+}

tests/Jellyfin.Server.Tests/HighAvailability/JellyfinSectionConfigurationTests.cs

@@ -13,6 +13,7 @@ namespace Jellyfin.Server.Tests.HighAvailability;
 /// startup configuration the host reads them from must therefore accept that form; when it does not,
 /// a correctly set variable is dropped and the feature it configures stays off without any error.
 /// </summary>
+[Collection("JellyfinSectionConfiguration")]
 public sealed class JellyfinSectionConfigurationTests : IDisposable
 {
     private const string RedisKey = "Jellyfin:TranscodeStore:RedisConnectionString";

tests/Jellyfin.Server.Tests/HighAvailability/RedisFaultProxy.cs

@@ -0,0 +1,170 @@
+using System;
+using System.Collections.Concurrent;
+using System.Globalization;
+using System.IO;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+using StackExchange.Redis;
+
+namespace Jellyfin.Server.Tests.HighAvailability;
+
+/// <summary>
+/// A loopback TCP proxy in front of a Redis server. Cutting it drops every connection through it and
+/// refuses new ones, so a test can take Redis away from one instance mid-flow - and give it back - the
+/// way a restarted valkey does, and watch what a real StackExchange.Redis client makes of it.
+/// </summary>
+public sealed class RedisFaultProxy : IAsyncDisposable
+{
+    private readonly ConcurrentDictionary<TcpClient, byte> _live = new();
+    private readonly CancellationTokenSource _cts = new();
+    private readonly TcpListener _listener;
+    private readonly string _targetHost;
+    private readonly int _targetPort;
+    private readonly int _port;
+
+    private volatile bool _cut;
+
+    private RedisFaultProxy(TcpListener listener, int port, string targetHost, int targetPort)
+    {
+        _listener = listener;
+        _port = port;
+        _targetHost = targetHost;
+        _targetPort = targetPort;
+    }
+
+    /// <summary>
+    /// Gets a connection string pointing at the proxy. The timeouts are short so a cut surfaces as a
+    /// failure in seconds rather than in the library's minute-scale defaults.
+    /// </summary>
+    public string ConnectionString => string.Create(
+        CultureInfo.InvariantCulture,
+        $"127.0.0.1:{_port},abortConnect=false,connectTimeout=500,syncTimeout=2000,connectRetry=1");
+
+    /// <summary>
+    /// Starts a proxy in front of the server named by <paramref name="target"/>.
+    /// </summary>
+    /// <param name="target">The connection string of the server to forward to.</param>
+    /// <returns>The running proxy.</returns>
+    public static RedisFaultProxy Start(string target)
+    {
+        var endpoint = ConfigurationOptions.Parse(target).EndPoints[0];
+        var (host, port) = endpoint switch
+        {
+            DnsEndPoint dns => (dns.Host, dns.Port),
+            IPEndPoint ip => (ip.Address.ToString(), ip.Port),
+            _ => throw new NotSupportedException("Unsupported endpoint " + endpoint)
+        };
+
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+
+        var proxy = new RedisFaultProxy(listener, ((IPEndPoint)listener.LocalEndpoint).Port, host, port);
+        _ = Task.Run(proxy.AcceptAsync);
+        return proxy;
+    }
+
+    /// <summary>
+    /// Takes Redis away from everything connected through the proxy.
+    /// </summary>
+    public void Cut()
+    {
+        _cut = true;
+        DropLiveConnections();
+    }
+
+    /// <summary>
+    /// Lets connections through again. Clients reconnect on their own schedule, so callers have to wait
+    /// for the connection to come back rather than assume it already has.
+    /// </summary>
+    public void Restore() => _cut = false;
+
+    /// <inheritdoc/>
+    public async ValueTask DisposeAsync()
+    {
+        _cut = true;
+        await _cts.CancelAsync().ConfigureAwait(false);
+        _listener.Stop();
+        DropLiveConnections();
+        _cts.Dispose();
+    }
+
+    private void DropLiveConnections()
+    {
+        foreach (var client in _live.Keys)
+        {
+            if (_live.TryRemove(client, out _))
+            {
+                client.Dispose();
+            }
+        }
+    }
+
+    private async Task AcceptAsync()
+    {
+        while (!_cts.IsCancellationRequested)
+        {
+            TcpClient client;
+            try
+            {
+                client = await _listener.AcceptTcpClientAsync(_cts.Token).ConfigureAwait(false);
+            }
+            catch (Exception exception) when (exception is OperationCanceledException or SocketException or ObjectDisposedException)
+            {
+                return;
+            }
+
+            if (_cut)
+            {
+                client.Dispose();
+                continue;
+            }
+
+            _ = Task.Run(() => ForwardAsync(client));
+        }
+    }
+
+    private async Task ForwardAsync(TcpClient client)
+    {
+        TcpClient? upstream = null;
+        try
+        {
+            upstream = new TcpClient();
+            await upstream.ConnectAsync(_targetHost, _targetPort, _cts.Token).ConfigureAwait(false);
+
+            _live[client] = 0;
+            _live[upstream] = 0;
+
+            var clientStream = client.GetStream();
+            var upstreamStream = upstream.GetStream();
+            await Task.WhenAny(
+                CopyAsync(clientStream, upstreamStream),
+                CopyAsync(upstreamStream, clientStream)).ConfigureAwait(false);
+        }
+        catch (Exception exception) when (exception is IOException or SocketException or OperationCanceledException or ObjectDisposedException)
+        {
+        }
+        finally
+        {
+            _live.TryRemove(client, out _);
+            client.Dispose();
+            if (upstream is not null)
+            {
+                _live.TryRemove(upstream, out _);
+                upstream.Dispose();
+            }
+        }
+    }
+
+    private async Task CopyAsync(NetworkStream from, NetworkStream to)
+    {
+        try
+        {
+            await from.CopyToAsync(to, _cts.Token).ConfigureAwait(false);
+        }
+        catch (Exception exception) when (exception is IOException or SocketException or OperationCanceledException or ObjectDisposedException)
+        {
+        }
+    }
+}

tests/Jellyfin.Server.Tests/HighAvailability/RedisTestServer.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Threading.Tasks;
+using StackExchange.Redis;
+using Testcontainers.Redis;
+
+namespace Jellyfin.Server.Tests.HighAvailability;
+
+/// <summary>
+/// Hands out a Redis server for the tests that need one. A server named by <c>JELLYFIN_TEST_REDIS</c> is
+/// used as is, so CI can run one beside the step instead of a docker daemon of its own; without it a
+/// container is started through testcontainers.
+/// </summary>
+public sealed class RedisTestServer : IAsyncDisposable
+{
+    /// <summary>
+    /// The connection string of an already running server.
+    /// </summary>
+    public const string ConnectionStringVariable = "JELLYFIN_TEST_REDIS";
+
+    private readonly RedisContainer? _container;
+
+    private RedisTestServer(RedisContainer? container, string connectionString)
+    {
+        _container = container;
+        ConnectionString = connectionString;
+    }
+
+    /// <summary>
+    /// Gets the connection string of the running server.
+    /// </summary>
+    public string ConnectionString { get; }
+
+    /// <summary>
+    /// Starts or attaches to a Redis server and waits until it accepts connections.
+    /// </summary>
+    /// <returns>The running server.</returns>
+    public static async Task<RedisTestServer> StartAsync()
+    {
+        var provided = Environment.GetEnvironmentVariable(ConnectionStringVariable);
+        if (!string.IsNullOrWhiteSpace(provided))
+        {
+            var attached = new RedisTestServer(null, provided);
+            await attached.WaitUntilReadyAsync().ConfigureAwait(false);
+            return attached;
+        }
+
+        var container = new RedisBuilder("redis:7-alpine").Build();
+        await container.StartAsync().ConfigureAwait(false);
+
+        var started = new RedisTestServer(container, container.GetConnectionString());
+        await started.WaitUntilReadyAsync().ConfigureAwait(false);
+        return started;
+    }
+
+    /// <summary>
+    /// Opens a connection of its own, so each in-process stand-in for a replica talks to the server the
+    /// way a separate pod would.
+    /// </summary>
+    /// <returns>A new multiplexer.</returns>
+    public async Task<IConnectionMultiplexer> ConnectAsync()
+        => await ConnectionMultiplexer.ConnectAsync(ConnectionString).ConfigureAwait(false);
+
+    /// <inheritdoc/>
+    public async ValueTask DisposeAsync()
+    {
+        if (_container is not null)
+        {
+            await _container.DisposeAsync().ConfigureAwait(false);
+        }
+    }
+
+    private async Task WaitUntilReadyAsync()
+    {
+        for (var attempt = 1; ; attempt++)
+        {
+            try
+            {
+                var connection = await ConnectionMultiplexer.ConnectAsync(ConnectionString).ConfigureAwait(false);
+                await using (connection.ConfigureAwait(false))
+                {
+                    await connection.GetDatabase().PingAsync().ConfigureAwait(false);
+                    return;
+                }
+            }
+            catch (RedisException) when (attempt < 60)
+            {
+                await Task.Delay(TimeSpan.FromSeconds(1)).ConfigureAwait(false);
+            }
+        }
+    }
+}

tests/Jellyfin.Server.Tests/Item/PostgreSqlNextUpServiceTests.cs

@@ -0,0 +1,234 @@
+using System;
+using System.Collections.Generic;
+using System.Security.Claims;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Data;
+using Jellyfin.Api.Constants;
+using Jellyfin.Api.Controllers;
+using Jellyfin.Database.Implementations;
+using Jellyfin.Database.Implementations.DbConfiguration;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Locking;
+using Jellyfin.Database.Providers.PostgreSQL;
+using Jellyfin.Server.Implementations.Item;
+using Jellyfin.Server.Tests.Migrations;
+using MediaBrowser.Controller.Dto;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Controller.Persistence;
+using MediaBrowser.Controller.TV;
+using MediaBrowser.Model.Querying;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Npgsql;
+using Xunit;
+using BaseItemKind = Jellyfin.Data.Enums.BaseItemKind;
+using User = Jellyfin.Database.Implementations.Entities.User;
+
+namespace Jellyfin.Server.Tests.Item;
+
+/// <summary>
+/// Drives the Next Up cutoff from the controller into a real PostgreSQL. The model binder hands a
+/// query-string date over as <see cref="DateTimeKind.Unspecified"/>, and Npgsql refuses to write anything
+/// but <see cref="DateTimeKind.Utc"/> to <c>timestamp with time zone</c>; SQLite takes every kind, so an
+/// unnormalised cutoff only ever fails here.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class PostgreSqlNextUpServiceTests : IAsyncLifetime
+{
+    private static readonly Guid _libraryId = Guid.Parse("aaaaaaaa-0000-0000-0000-000000000001");
+    private static readonly Guid _otherLibraryId = Guid.Parse("aaaaaaaa-0000-0000-0000-000000000002");
+    private static readonly Guid _userId = Guid.Parse("bbbbbbbb-0000-0000-0000-000000000001");
+
+    private static readonly Guid _recentWatchedId = Guid.Parse("cccccccc-0000-0000-0000-000000000001");
+    private static readonly Guid _recentOlderId = Guid.Parse("cccccccc-0000-0000-0000-000000000002");
+    private static readonly Guid _staleWatchedId = Guid.Parse("cccccccc-0000-0000-0000-000000000003");
+    private static readonly Guid _unwatchedId = Guid.Parse("cccccccc-0000-0000-0000-000000000004");
+    private static readonly Guid _foreignLibraryId = Guid.Parse("cccccccc-0000-0000-0000-000000000005");
+
+    private static readonly DateTime _recentPlayedAt = new DateTime(2026, 3, 1, 12, 0, 0, DateTimeKind.Utc);
+    private static readonly DateTime _stalePlayedAt = new DateTime(2020, 1, 1, 12, 0, 0, DateTimeKind.Utc);
+
+    private readonly ItemTypeLookup _itemTypeLookup = new();
+    private readonly User _user = new User("next-up", "auth", "reset") { Id = _userId };
+
+    private PostgreSqlTestServer _server = null!;
+    private NpgsqlDataSource _dataSource = null!;
+    private NextUpService _service = null!;
+
+    public async ValueTask InitializeAsync()
+    {
+        _server = await PostgreSqlTestServer.StartAsync().ConfigureAwait(false);
+        var connectionString = await _server.CreateDatabaseAsync("next_up_service", TestContext.Current.CancellationToken).ConfigureAwait(false);
+        _dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+
+        var context = CreateDbContext();
+        await using (context.ConfigureAwait(false))
+        {
+            await context.Database.EnsureCreatedAsync(TestContext.Current.CancellationToken).ConfigureAwait(false);
+        }
+
+        var factory = new Mock<IDbContextFactory<JellyfinDbContext>>();
+        factory.Setup(f => f.CreateDbContext()).Returns(CreateDbContext);
+        factory.Setup(f => f.CreateDbContextAsync(It.IsAny<CancellationToken>())).ReturnsAsync(CreateDbContext);
+
+        _service = new NextUpService(factory.Object, _itemTypeLookup, new Mock<IItemQueryHelpers>().Object);
+
+        await SeedAsync().ConfigureAwait(false);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _dataSource.DisposeAsync().ConfigureAwait(false);
+        await _server.DisposeAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// A cutoff on the query string, which the model binder leaves unspecified.
+    /// </summary>
+    [Fact]
+    public void GetNextUpSeriesKeys_WithSuppliedCutoff_DropsSeriesPlayedBeforeIt()
+    {
+        var cutoff = RunController(new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Unspecified)).NextUpDateCutoff;
+
+        var keys = _service.GetNextUpSeriesKeys(CreateFilter(), cutoff);
+
+        Assert.Equal(new[] { "series-recent" }, keys);
+    }
+
+    /// <summary>
+    /// The home-screen row, where the client sends no cutoff and the query default stands in.
+    /// </summary>
+    [Fact]
+    public void GetNextUpSeriesKeys_WithoutSuppliedCutoff_ReturnsWatchedSeriesNewestFirst()
+    {
+        var cutoff = RunController(null).NextUpDateCutoff;
+
+        var keys = _service.GetNextUpSeriesKeys(CreateFilter(), cutoff);
+
+        Assert.Equal(new[] { "series-recent", "series-stale" }, keys);
+    }
+
+    /// <summary>
+    /// Calls <c>GET /Shows/NextUp</c> and hands back the query it built for the series lookup.
+    /// </summary>
+    private NextUpQuery RunController(DateTime? nextUpDateCutoff)
+    {
+        var userManager = new Mock<IUserManager>();
+        userManager.Setup(m => m.GetUserById(_userId)).Returns(_user);
+
+        var dtoService = new Mock<IDtoService>();
+        dtoService.Setup(s => s.GetBaseItemDtos(
+                It.IsAny<IReadOnlyList<BaseItem>>(),
+                It.IsAny<DtoOptions>(),
+                It.IsAny<User>(),
+                It.IsAny<BaseItem>(),
+                It.IsAny<bool>()))
+            .Returns([]);
+
+        NextUpQuery? captured = null;
+        var tvSeriesManager = new Mock<ITVSeriesManager>();
+        tvSeriesManager.Setup(m => m.GetNextUp(It.IsAny<NextUpQuery>(), It.IsAny<DtoOptions>()))
+            .Callback<NextUpQuery, DtoOptions>((query, _) => captured = query)
+            .Returns(new QueryResult<BaseItem>());
+
+        var controller = new TvShowsController(
+            userManager.Object,
+            new Mock<ILibraryManager>().Object,
+            dtoService.Object,
+            tvSeriesManager.Object)
+        {
+            ControllerContext = new ControllerContext
+            {
+                HttpContext = new DefaultHttpContext
+                {
+                    User = new ClaimsPrincipal(new ClaimsIdentity([new Claim(InternalClaimTypes.UserId, _userId.ToString("D"))], "Test"))
+                }
+            }
+        };
+
+        controller.GetNextUp(null, null, null, [], null, null, null, null, [], null, nextUpDateCutoff);
+
+        return captured!;
+    }
+
+    private InternalItemsQuery CreateFilter()
+    {
+        return new InternalItemsQuery(_user) { TopParentIds = [_libraryId] };
+    }
+
+    private JellyfinDbContext CreateDbContext()
+    {
+        var optionsBuilder = new DbContextOptionsBuilder<JellyfinDbContext>();
+        var provider = new PostgreSqlDatabaseProvider(_dataSource);
+        provider.Initialise(optionsBuilder, new DatabaseConfigurationOptions { DatabaseType = "PostgreSQL" });
+        return new JellyfinDbContext(
+            optionsBuilder.Options,
+            NullLogger<JellyfinDbContext>.Instance,
+            provider,
+            new NoLockBehavior(NullLogger<NoLockBehavior>.Instance));
+    }
+
+    private async Task SeedAsync()
+    {
+        var context = CreateDbContext();
+        await using (context.ConfigureAwait(false))
+        {
+            context.Users.Add(_user);
+
+            // The newest play of a series decides its place, so the older episode must not pull it down.
+            var recentWatched = AddEpisode(context, _recentWatchedId, "series-recent", _libraryId);
+            AddUserData(context, recentWatched, _recentPlayedAt);
+            var recentOlder = AddEpisode(context, _recentOlderId, "series-recent", _libraryId);
+            AddUserData(context, recentOlder, _stalePlayedAt);
+
+            var staleWatched = AddEpisode(context, _staleWatchedId, "series-stale", _libraryId);
+            AddUserData(context, staleWatched, _stalePlayedAt);
+
+            // Never played, and played but outside the requested libraries: both stay out.
+            AddEpisode(context, _unwatchedId, "series-unwatched", _libraryId);
+            var foreign = AddEpisode(context, _foreignLibraryId, "series-foreign", _otherLibraryId);
+            AddUserData(context, foreign, _recentPlayedAt);
+
+            await context.SaveChangesAsync(TestContext.Current.CancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    private BaseItemEntity AddEpisode(JellyfinDbContext context, Guid id, string seriesKey, Guid topParentId)
+    {
+        var episode = new BaseItemEntity
+        {
+            Id = id,
+            Type = _itemTypeLookup.BaseItemKindNames[BaseItemKind.Episode],
+            Name = seriesKey + "-" + id.ToString("N"),
+            SeriesPresentationUniqueKey = seriesKey,
+            PresentationUniqueKey = id.ToString("N"),
+            TopParentId = topParentId,
+            MediaType = "Video",
+            IsFolder = false,
+            IsVirtualItem = false
+        };
+
+        context.BaseItems.Add(episode);
+        return episode;
+    }
+
+    private void AddUserData(JellyfinDbContext context, BaseItemEntity item, DateTime lastPlayedDate)
+    {
+        context.UserData.Add(new UserData
+        {
+            CustomDataKey = item.Id.ToString("N"),
+            ItemId = item.Id,
+            Item = item,
+            UserId = _userId,
+            User = _user,
+            LastPlayedDate = lastPlayedDate,
+            Played = true,
+            PlayCount = 1
+        });
+    }
+}

tests/Jellyfin.Server.Tests/Jellyfin.Server.Tests.csproj

@@ -12,6 +12,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="Npgsql" />
     <PackageReference Include="Testcontainers.PostgreSql" />
+    <PackageReference Include="Testcontainers.Redis" />
     <PackageReference Include="xunit.v3" />
     <PackageReference Include="xunit.runner.visualstudio">
       <PrivateAssets>all</PrivateAssets>

tests/Jellyfin.Server.Tests/Library/UserDataManagerReplicaTests.cs

@@ -0,0 +1,243 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Library;
+using Jellyfin.Database.Implementations;
+using Jellyfin.Database.Implementations.DbConfiguration;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Locking;
+using Jellyfin.Database.Providers.PostgreSQL;
+using Jellyfin.Server.Tests.Migrations;
+using MediaBrowser.Controller.Configuration;
+using MediaBrowser.Model.Configuration;
+using MediaBrowser.Model.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Npgsql;
+using Xunit;
+using AudioBook = MediaBrowser.Controller.Entities.AudioBook;
+
+namespace Jellyfin.Server.Tests.Library;
+
+/// <summary>
+/// Two independently constructed <see cref="UserDataManager"/> instances over one PostgreSQL database are the
+/// in-process stand-in for two replicas sharing one database: what either of them writes, the other has to
+/// see on its very next read, and a read-modify-write on one must not roll back the other's.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class UserDataManagerReplicaTests : IClassFixture<UserDataManagerReplicaTests.DatabaseFixture>
+{
+    private static readonly long _quarterIn = TimeSpan.FromMinutes(20).Ticks;
+
+    private readonly NpgsqlDataSource _dataSource;
+
+    public UserDataManagerReplicaTests(DatabaseFixture fixture)
+    {
+        _dataSource = fixture.DataSource;
+    }
+
+    /// <summary>
+    /// A resume position written by the replica serving the playback tick has to be the position the next
+    /// request reads, whichever replica it lands on - both through the single item read the write path uses
+    /// and through the batch read the library pages render from.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task ResumePositionWrittenOnOneReplica_IsReadOnAnother()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var itemId = Guid.NewGuid();
+        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
+
+        var replicaA = CreateManager(_dataSource);
+        var replicaB = CreateManager(_dataSource);
+        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
+        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
+
+        var early = replicaA.GetUserData(user, itemOnA)!;
+        early.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
+        replicaA.SaveUserData(user, itemOnA, early, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        // Replica B materialised the item before the later tick, so it holds the earlier row in memory.
+        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
+
+        var later = replicaA.GetUserData(user, itemOnA)!;
+        later.PlaybackPositionTicks = _quarterIn;
+        replicaA.SaveUserData(user, itemOnA, later, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        Assert.Equal(_quarterIn, replicaB.GetUserData(user, itemOnB)!.PlaybackPositionTicks);
+        Assert.Equal(_quarterIn, replicaB.GetUserDataBatch([itemOnB], user)[itemId].PlaybackPositionTicks);
+    }
+
+    /// <summary>
+    /// The playback tick is a read-modify-write of the whole row, so a tick served by one replica must build
+    /// on the favourite another replica just recorded instead of writing it back out.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task PlaybackTickOnOneReplica_KeepsFavouriteSetOnAnother()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var itemId = Guid.NewGuid();
+        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
+
+        var replicaA = CreateManager(_dataSource);
+        var replicaB = CreateManager(_dataSource);
+        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
+        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
+
+        var seed = replicaA.GetUserData(user, itemOnA)!;
+        seed.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
+        replicaA.SaveUserData(user, itemOnA, seed, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        // Replica B is serving the playback session and read the item before the favourite was recorded.
+        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
+
+        var favourited = replicaA.GetUserData(user, itemOnA)!;
+        favourited.IsFavorite = true;
+        replicaA.SaveUserData(user, itemOnA, favourited, UserDataSaveReason.UpdateUserRating, cancellationToken);
+
+        var tick = replicaB.GetUserData(user, itemOnB)!;
+        tick.PlaybackPositionTicks = _quarterIn;
+        replicaB.SaveUserData(user, itemOnB, tick, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        var stored = replicaA.GetUserData(user, itemOnA)!;
+        Assert.True(stored.IsFavorite);
+        Assert.Equal(_quarterIn, stored.PlaybackPositionTicks);
+    }
+
+    /// <summary>
+    /// A tick that lands on the other replica has to carry the position forward from where the session
+    /// actually is, not from the position that replica happened to have in memory.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task PlaybackTickOnOneReplica_ResumesFromThePositionAnotherWrote()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var itemId = Guid.NewGuid();
+        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
+
+        var replicaA = CreateManager(_dataSource);
+        var replicaB = CreateManager(_dataSource);
+        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
+        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
+
+        var seed = replicaA.GetUserData(user, itemOnA)!;
+        seed.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
+        replicaA.SaveUserData(user, itemOnA, seed, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
+
+        // The viewer seeks forward and the tick reporting it lands on replica A.
+        var seeked = replicaA.GetUserData(user, itemOnA)!;
+        seeked.PlaybackPositionTicks = _quarterIn;
+        replicaA.SaveUserData(user, itemOnA, seeked, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        // The next tick lands on replica B, which adds ten seconds to whatever it reads.
+        var tick = replicaB.GetUserData(user, itemOnB)!;
+        tick.PlaybackPositionTicks += TimeSpan.FromSeconds(10).Ticks;
+        replicaB.SaveUserData(user, itemOnB, tick, UserDataSaveReason.PlaybackProgress, cancellationToken);
+
+        var stored = replicaA.GetUserData(user, itemOnA)!;
+        Assert.Equal(_quarterIn + TimeSpan.FromSeconds(10).Ticks, stored.PlaybackPositionTicks);
+    }
+
+    private static UserDataManager CreateManager(NpgsqlDataSource dataSource)
+    {
+        var config = new Mock<IServerConfigurationManager>();
+        config.SetupGet(c => c.Configuration).Returns(new ServerConfiguration());
+        return new UserDataManager(config.Object, new DataSourceContextFactory(dataSource));
+    }
+
+    private static async Task<ICollection<UserData>> LoadUserDataAsync(NpgsqlDataSource dataSource, Guid itemId, CancellationToken cancellationToken)
+    {
+        var context = CreateContext(dataSource);
+        await using (context.ConfigureAwait(false))
+        {
+            return await context.UserData
+                .AsNoTracking()
+                .Where(e => e.ItemId.Equals(itemId))
+                .ToArrayAsync(cancellationToken)
+                .ConfigureAwait(false);
+        }
+    }
+
+    private static async Task<User> CreateUserAndItemAsync(NpgsqlDataSource dataSource, Guid itemId, CancellationToken cancellationToken)
+    {
+        var context = CreateContext(dataSource);
+        await using (context.ConfigureAwait(false))
+        {
+            var user = new User("replica-user-" + itemId.ToString("N", CultureInfo.InvariantCulture), "provider", "provider");
+            context.Users.Add(user);
+            context.BaseItems.Add(new BaseItemEntity { Id = itemId, Type = typeof(AudioBook).FullName! });
+            await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
+
+            return user;
+        }
+    }
+
+    private static JellyfinDbContext CreateContext(NpgsqlDataSource dataSource)
+    {
+        var optionsBuilder = new DbContextOptionsBuilder<JellyfinDbContext>();
+        var provider = new PostgreSqlDatabaseProvider(dataSource);
+        provider.Initialise(optionsBuilder, new DatabaseConfigurationOptions { DatabaseType = "PostgreSQL" });
+        return new JellyfinDbContext(
+            optionsBuilder.Options,
+            NullLogger<JellyfinDbContext>.Instance,
+            provider,
+            new NoLockBehavior(NullLogger<NoLockBehavior>.Instance));
+    }
+
+    /// <summary>
+    /// Hands every <see cref="UserDataManager"/> its own context over the one shared database, the way the
+    /// pooled factory does in the server.
+    /// </summary>
+    private sealed class DataSourceContextFactory : IDbContextFactory<JellyfinDbContext>
+    {
+        private readonly NpgsqlDataSource _dataSource;
+
+        public DataSourceContextFactory(NpgsqlDataSource dataSource)
+        {
+            _dataSource = dataSource;
+        }
+
+        public JellyfinDbContext CreateDbContext() => CreateContext(_dataSource);
+    }
+
+    /// <summary>
+    /// Builds the schema once for the whole class. Every test keeps to its own user and item, so one
+    /// database serves all of them and the shared server is spared three schema builds.
+    /// </summary>
+    public sealed class DatabaseFixture : IAsyncLifetime
+    {
+        private PostgreSqlTestServer _server = null!;
+
+        public NpgsqlDataSource DataSource { get; private set; } = null!;
+
+        /// <inheritdoc/>
+        public async ValueTask InitializeAsync()
+        {
+            _server = await PostgreSqlTestServer.StartAsync().ConfigureAwait(false);
+            var connectionString = await _server.CreateDatabaseAsync("userdata_replica", CancellationToken.None).ConfigureAwait(false);
+            DataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+
+            var context = CreateContext(DataSource);
+            await using (context.ConfigureAwait(false))
+            {
+                await context.Database.EnsureCreatedAsync(CancellationToken.None).ConfigureAwait(false);
+            }
+        }
+
+        /// <inheritdoc/>
+        public async ValueTask DisposeAsync()
+        {
+            await DataSource.DisposeAsync().ConfigureAwait(false);
+            await _server.DisposeAsync().ConfigureAwait(false);
+        }
+    }
+}

tests/Jellyfin.Server.Tests/QuickConnect/QuickConnectReplicaTests.cs

@@ -0,0 +1,369 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.QuickConnect;
+using Jellyfin.Data.Queries;
+using Jellyfin.Database.Implementations;
+using Jellyfin.Database.Implementations.DbConfiguration;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Entities.Security;
+using Jellyfin.Database.Implementations.Locking;
+using Jellyfin.Database.Providers.PostgreSQL;
+using Jellyfin.Server.Implementations.Devices;
+using Jellyfin.Server.Tests.HighAvailability;
+using Jellyfin.Server.Tests.Migrations;
+using MediaBrowser.Common.Extensions;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Controller.Configuration;
+using MediaBrowser.Controller.Devices;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Controller.Net;
+using MediaBrowser.Controller.QuickConnect;
+using MediaBrowser.Controller.Session;
+using MediaBrowser.Model.Configuration;
+using MediaBrowser.Model.Dto;
+using MediaBrowser.Model.QuickConnect;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Npgsql;
+using StackExchange.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Tests.QuickConnect;
+
+/// <summary>
+/// Three independently constructed <see cref="QuickConnectManager"/> instances over one PostgreSQL
+/// database and one Redis are the in-process stand-in for three replicas without sticky sessions: the
+/// initiate, authorize and exchange legs of one flow each land on a different one.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class QuickConnectReplicaTests : IAsyncLifetime
+{
+    private static readonly AuthorizationInfo _authorizationInfo = new AuthorizationInfo
+    {
+        Device = "Living Room TV",
+        DeviceId = "device-1",
+        Client = "Jellyfin Web",
+        Version = "1.0.0"
+    };
+
+    private readonly List<IConnectionMultiplexer> _connections = new();
+
+    private PostgreSqlTestServer _postgres = null!;
+    private RedisTestServer _redis = null!;
+
+    /// <inheritdoc/>
+    public async ValueTask InitializeAsync()
+    {
+        _postgres = await PostgreSqlTestServer.StartAsync().ConfigureAwait(false);
+        _redis = await RedisTestServer.StartAsync().ConfigureAwait(false);
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask DisposeAsync()
+    {
+        foreach (var connection in _connections)
+        {
+            await connection.DisposeAsync().ConfigureAwait(false);
+        }
+
+        await _redis.DisposeAsync().ConfigureAwait(false);
+        await _postgres.DisposeAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// The three legs of a quick connect flow land on three different replicas, and the token the third
+    /// one hands out is the one the second one minted into the shared database.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task InitiateAuthorizeExchange_AcrossThreeReplicas_Succeeds()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var connectionString = await _postgres.CreateDatabaseAsync("quickconnect_replica_flow", cancellationToken);
+
+        await using var dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+        var user = await CreateSchemaWithUserAsync(dataSource, cancellationToken);
+
+        var replicaA = await CreateReplicaAsync(dataSource, user);
+        var replicaB = await CreateReplicaAsync(dataSource, user);
+        var replicaC = await CreateReplicaAsync(dataSource, user);
+
+        var initiated = await replicaA.Manager.TryConnect(_authorizationInfo);
+
+        // The code is shown to the user on whichever replica serves the dashboard.
+        Assert.True(await replicaB.Manager.AuthorizeRequest(user.Id, initiated.Code));
+
+        var polled = await replicaC.Manager.CheckRequestStatus(initiated.Secret);
+        Assert.True(polled.Authenticated);
+        Assert.Equal(initiated.Code, polled.Code);
+        Assert.Equal(_authorizationInfo.DeviceId, polled.DeviceId);
+
+        var exchanged = await replicaC.Manager.GetAuthorizedRequest(initiated.Secret);
+
+        Assert.False(string.IsNullOrEmpty(exchanged.AccessToken));
+        Assert.Equal(user.Id, exchanged.User.Id);
+
+        var devices = await replicaA.Devices.GetDevices(new DeviceQuery { AccessToken = exchanged.AccessToken });
+        Assert.Equal(user.Id, Assert.Single(devices.Items).UserId);
+    }
+
+    /// <summary>
+    /// A secret is single use across the whole deployment: two replicas racing to exchange it must not
+    /// both hand out an access token. One scheduling of one race settles nothing either way, so the race
+    /// is run repeatedly.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Exchange_RacedOnTwoReplicas_SucceedsOnce()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var connectionString = await _postgres.CreateDatabaseAsync("quickconnect_replica_race", cancellationToken);
+
+        await using var dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+        var user = await CreateSchemaWithUserAsync(dataSource, cancellationToken);
+
+        var replicaA = await CreateReplicaAsync(dataSource, user);
+        var replicaB = await CreateReplicaAsync(dataSource, user);
+        var replicaC = await CreateReplicaAsync(dataSource, user);
+
+        for (var attempt = 0; attempt < 25; attempt++)
+        {
+            var initiated = await replicaA.Manager.TryConnect(AuthorizationInfoFor(attempt));
+            await replicaB.Manager.AuthorizeRequest(user.Id, initiated.Code);
+
+            var outcomes = await Task.WhenAll(
+                Task.Run(() => ExchangeAsync(replicaA.Manager, initiated.Secret), cancellationToken),
+                Task.Run(() => ExchangeAsync(replicaC.Manager, initiated.Secret), cancellationToken));
+
+            Assert.Single(outcomes, outcome => outcome is not null);
+
+            // And it stays consumed for every later attempt, on any replica.
+            await Assert.ThrowsAsync<ResourceNotFoundException>(() => replicaB.Manager.GetAuthorizedRequest(initiated.Secret));
+        }
+    }
+
+    /// <summary>
+    /// Two replicas authorizing one code at the same time mint one access token between them. A second
+    /// one would be live, attached to the same device and reachable by nobody.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Authorize_RacedOnTwoReplicas_MintsOneAccessToken()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var connectionString = await _postgres.CreateDatabaseAsync("quickconnect_replica_authorize_race", cancellationToken);
+
+        await using var dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+        var user = await CreateSchemaWithUserAsync(dataSource, cancellationToken);
+
+        var replicaA = await CreateReplicaAsync(dataSource, user);
+        var replicaB = await CreateReplicaAsync(dataSource, user);
+        var replicaC = await CreateReplicaAsync(dataSource, user);
+
+        for (var attempt = 0; attempt < 20; attempt++)
+        {
+            var authorizationInfo = AuthorizationInfoFor(attempt);
+            var initiated = await replicaA.Manager.TryConnect(authorizationInfo);
+
+            var outcomes = await Task.WhenAll(
+                Task.Run(() => AuthorizeAsync(replicaB.Manager, user.Id, initiated.Code), cancellationToken),
+                Task.Run(() => AuthorizeAsync(replicaC.Manager, user.Id, initiated.Code), cancellationToken));
+
+            Assert.Single(outcomes, authorized => authorized);
+
+            var devices = await replicaA.Devices.GetDevices(new DeviceQuery { DeviceId = authorizationInfo.DeviceId });
+            var device = Assert.Single(devices.Items);
+
+            var exchanged = await replicaA.Manager.GetAuthorizedRequest(initiated.Secret);
+            Assert.Equal(device.AccessToken, exchanged.AccessToken);
+        }
+    }
+
+    /// <summary>
+    /// An expired request is rejected on a replica that never saw it created, rather than resolving to a
+    /// stale authorization.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task ExpiredRequest_IsRejectedOnEveryReplica()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var connectionString = await _postgres.CreateDatabaseAsync("quickconnect_replica_expiry", cancellationToken);
+
+        await using var dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+        var user = await CreateSchemaWithUserAsync(dataSource, cancellationToken);
+
+        var replicaA = await CreateReplicaAsync(dataSource, user);
+        var replicaB = await CreateReplicaAsync(dataSource, user);
+
+        var initiated = await replicaA.Manager.TryConnect(_authorizationInfo);
+        Assert.NotNull(await replicaB.Manager.CheckRequestStatus(initiated.Secret));
+
+        // Shorten the stored expiry instead of waiting out the ten minute timeout.
+        await replicaA.Store.SetRequestAsync(initiated, DateTime.UtcNow.AddSeconds(1), cancellationToken);
+        await Task.Delay(TimeSpan.FromSeconds(2), cancellationToken);
+
+        await Assert.ThrowsAsync<ResourceNotFoundException>(() => replicaB.Manager.CheckRequestStatus(initiated.Secret));
+        await Assert.ThrowsAsync<ResourceNotFoundException>(() => replicaB.Manager.AuthorizeRequest(user.Id, initiated.Code));
+    }
+
+    /// <summary>
+    /// An authorization that was never exchanged expires too, so a code authorized and then abandoned
+    /// cannot be redeemed later from another replica.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task ExpiredAuthorization_IsRejectedOnEveryReplica()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var connectionString = await _postgres.CreateDatabaseAsync("quickconnect_replica_auth_expiry", cancellationToken);
+
+        await using var dataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
+        var user = await CreateSchemaWithUserAsync(dataSource, cancellationToken);
+
+        var replicaA = await CreateReplicaAsync(dataSource, user);
+        var replicaB = await CreateReplicaAsync(dataSource, user);
+
+        var initiated = await replicaA.Manager.TryConnect(_authorizationInfo);
+        await replicaA.Manager.AuthorizeRequest(user.Id, initiated.Code);
+
+        var stored = await replicaA.Store.GetRequestBySecretAsync(initiated.Secret, cancellationToken);
+        Assert.True(stored?.Authenticated);
+
+        await replicaA.Store.SetAuthorizationAsync(
+            initiated.Secret,
+            new AuthenticationResult { AccessToken = "stale" },
+            DateTime.UtcNow.AddSeconds(1),
+            cancellationToken);
+        await Task.Delay(TimeSpan.FromSeconds(2), cancellationToken);
+
+        await Assert.ThrowsAsync<ResourceNotFoundException>(() => replicaB.Manager.GetAuthorizedRequest(initiated.Secret));
+    }
+
+    private static AuthorizationInfo AuthorizationInfoFor(int attempt) => new AuthorizationInfo
+    {
+        Device = _authorizationInfo.Device,
+        DeviceId = string.Create(CultureInfo.InvariantCulture, $"device-{attempt}"),
+        Client = _authorizationInfo.Client,
+        Version = _authorizationInfo.Version
+    };
+
+    private static async Task<bool> AuthorizeAsync(IQuickConnect manager, Guid userId, string code)
+    {
+        try
+        {
+            return await manager.AuthorizeRequest(userId, code).ConfigureAwait(false);
+        }
+        catch (InvalidOperationException)
+        {
+            return false;
+        }
+    }
+
+    private static async Task<AuthenticationResult?> ExchangeAsync(IQuickConnect manager, string secret)
+    {
+        try
+        {
+            return await manager.GetAuthorizedRequest(secret).ConfigureAwait(false);
+        }
+        catch (ResourceNotFoundException)
+        {
+            return null;
+        }
+    }
+
+    private static async Task<User> CreateSchemaWithUserAsync(NpgsqlDataSource dataSource, CancellationToken cancellationToken)
+    {
+        var context = CreateContext(dataSource);
+        await using (context.ConfigureAwait(false))
+        {
+            await context.Database.EnsureCreatedAsync(cancellationToken).ConfigureAwait(false);
+
+            var user = new User("quickconnect-user", "provider", "provider");
+            context.Users.Add(user);
+            await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
+
+            return user;
+        }
+    }
+
+    private static JellyfinDbContext CreateContext(NpgsqlDataSource dataSource)
+    {
+        var optionsBuilder = new DbContextOptionsBuilder<JellyfinDbContext>();
+        var provider = new PostgreSqlDatabaseProvider(dataSource);
+        provider.Initialise(optionsBuilder, new DatabaseConfigurationOptions { DatabaseType = "PostgreSQL" });
+        return new JellyfinDbContext(
+            optionsBuilder.Options,
+            NullLogger<JellyfinDbContext>.Instance,
+            provider,
+            new NoLockBehavior(NullLogger<NoLockBehavior>.Instance));
+    }
+
+    private async Task<Replica> CreateReplicaAsync(NpgsqlDataSource dataSource, User user)
+    {
+        var connection = await _redis.ConnectAsync().ConfigureAwait(false);
+        _connections.Add(connection);
+
+        var userManager = new Mock<IUserManager>();
+        userManager.Setup(manager => manager.GetUserById(user.Id)).Returns(user);
+        var deviceManager = new DeviceManager(new DataSourceContextFactory(dataSource), userManager.Object);
+
+        var configManager = new Mock<IServerConfigurationManager>();
+        configManager.Setup(manager => manager.Configuration).Returns(new ServerConfiguration { QuickConnectAvailable = true });
+
+        // Stands in for SessionManager.AuthenticateDirect: the token has to be minted into the shared
+        // database, because the replica that exchanges the secret is not the one that authorized it.
+        var sessionManager = new Mock<ISessionManager>();
+        sessionManager
+            .Setup(manager => manager.AuthenticateDirect(It.IsAny<AuthenticationRequest>()))
+            .Returns<AuthenticationRequest>(async request =>
+            {
+                var device = await deviceManager.CreateDevice(
+                    new Device(request.UserId, request.App, request.AppVersion, request.DeviceName, request.DeviceId)).ConfigureAwait(false);
+
+                return new AuthenticationResult
+                {
+                    AccessToken = device.AccessToken,
+                    ServerId = "server-1",
+                    User = new UserDto { Id = user.Id, Name = user.Username, ServerId = "server-1" },
+                    SessionInfo = new SessionInfoDto
+                    {
+                        Id = device.Id.ToString(CultureInfo.InvariantCulture),
+                        UserId = user.Id,
+                        UserName = user.Username,
+                        Client = request.App,
+                        DeviceId = request.DeviceId,
+                        DeviceName = request.DeviceName,
+                        ApplicationVersion = request.AppVersion
+                    }
+                };
+            });
+
+        var store = new RedisQuickConnectStore(connection, NullLogger<RedisQuickConnectStore>.Instance);
+        var manager = new QuickConnectManager(
+            configManager.Object,
+            NullLogger<QuickConnectManager>.Instance,
+            sessionManager.Object,
+            store);
+
+        return new Replica(manager, store, deviceManager);
+    }
+
+    private sealed record Replica(IQuickConnect Manager, IQuickConnectStore Store, IDeviceManager Devices);
+
+    private sealed class DataSourceContextFactory : IDbContextFactory<JellyfinDbContext>
+    {
+        private readonly NpgsqlDataSource _dataSource;
+
+        public DataSourceContextFactory(NpgsqlDataSource dataSource)
+        {
+            _dataSource = dataSource;
+        }
+
+        public JellyfinDbContext CreateDbContext() => CreateContext(_dataSource);
+    }
+}

tests/Jellyfin.Server.Tests/QuickConnect/QuickConnectStoreWiringTests.cs

@@ -0,0 +1,142 @@
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.QuickConnect;
+using Jellyfin.Server.Extensions;
+using Jellyfin.Server.Tests.HighAvailability;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Controller.QuickConnect;
+using MediaBrowser.Model.QuickConnect;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using StackExchange.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Tests.QuickConnect;
+
+/// <summary>
+/// Drives the whole configuration path a deployment uses: a bare
+/// <c>Jellyfin__TranscodeStore__RedisConnectionString</c> environment variable, the server's own
+/// configuration builder, the store registration, and a quick connect flow against a real valkey.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+[Collection("JellyfinSectionConfiguration")]
+public sealed class QuickConnectStoreWiringTests : IAsyncLifetime
+{
+    private const string RedisConnectionStringVariable = "Jellyfin__TranscodeStore__RedisConnectionString";
+
+    private RedisTestServer _redis = null!;
+    private string _configDirectory = string.Empty;
+
+    /// <inheritdoc/>
+    public async ValueTask InitializeAsync()
+    {
+        _redis = await RedisTestServer.StartAsync().ConfigureAwait(false);
+        _configDirectory = Directory.CreateTempSubdirectory("jellyfin-quickconnect-wiring").FullName;
+        await File.WriteAllTextAsync(Path.Combine(_configDirectory, "logging.default.json"), "{}").ConfigureAwait(false);
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask DisposeAsync()
+    {
+        Environment.SetEnvironmentVariable(RedisConnectionStringVariable, null);
+
+        if (_configDirectory.Length > 0)
+        {
+            Directory.Delete(_configDirectory, true);
+        }
+
+        await _redis.DisposeAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// The variable form deployments set selects the shared store, and that store really talks to valkey.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task ManifestStyleEnvironmentVariable_SelectsTheSharedStore()
+    {
+        Environment.SetEnvironmentVariable(RedisConnectionStringVariable, _redis.ConnectionString + ",abortConnect=false");
+
+        await using var provider = BuildProvider();
+
+        var store = provider.GetRequiredService<IQuickConnectStore>();
+        Assert.IsType<RedisQuickConnectStore>(store);
+
+        var request = NewRequest();
+        await store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), TestContext.Current.CancellationToken);
+
+        Assert.True(await store.TryClaimAuthorizationAsync(request.Secret, DateTime.UtcNow.AddMinutes(10), TestContext.Current.CancellationToken));
+
+        var redis = provider.GetRequiredService<IConnectionMultiplexer>();
+        Assert.True(await redis.GetDatabase().KeyExistsAsync("jellyfin:quickconnect:request:" + request.Secret));
+    }
+
+    /// <summary>
+    /// Without the variable the deployment is single-instance and gets the process-local store.
+    /// </summary>
+    [Fact]
+    public void NoEnvironmentVariable_SelectsTheProcessLocalStore()
+    {
+        Environment.SetEnvironmentVariable(RedisConnectionStringVariable, null);
+
+        using var provider = BuildProvider();
+
+        Assert.IsType<InMemoryQuickConnectStore>(provider.GetRequiredService<IQuickConnectStore>());
+    }
+
+    /// <summary>
+    /// A configured but unreachable Redis degrades to the single-instance behaviour of a flow having to
+    /// complete against one instance, rather than taking quick connect down at startup.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task UnreachableRedisAtStartup_DegradesToTheProcessLocalStore()
+    {
+        Environment.SetEnvironmentVariable(RedisConnectionStringVariable, "127.0.0.1:1,connectTimeout=250,connectRetry=0");
+
+        await using var provider = BuildProvider();
+
+        var store = provider.GetRequiredService<IQuickConnectStore>();
+        Assert.IsType<InMemoryQuickConnectStore>(store);
+
+        // Quick connect still works, it just cannot span instances.
+        var request = NewRequest();
+        await store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), TestContext.Current.CancellationToken);
+        Assert.True(await store.TryClaimAuthorizationAsync(request.Secret, DateTime.UtcNow.AddMinutes(10), TestContext.Current.CancellationToken));
+        await store.SetAuthorizationAsync(
+            request.Secret,
+            new AuthenticationResult { AccessToken = "token-1" },
+            DateTime.UtcNow.AddMinutes(10),
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal("token-1", (await store.TryConsumeAuthorizationAsync(request.Secret, TestContext.Current.CancellationToken))?.AccessToken);
+        Assert.Null(await store.TryConsumeAuthorizationAsync(request.Secret, TestContext.Current.CancellationToken));
+    }
+
+    private static QuickConnectResult NewRequest() => new QuickConnectResult(
+        Guid.NewGuid().ToString("N"),
+        Guid.NewGuid().ToString("N").Substring(0, 6),
+        DateTime.UtcNow,
+        "device-1",
+        "Living Room TV",
+        "Jellyfin Web",
+        "1.0.0");
+
+    private ServiceProvider BuildProvider()
+    {
+        var appPaths = new Mock<IApplicationPaths>();
+        appPaths.Setup(paths => paths.ConfigurationDirectoryPath).Returns(_configDirectory);
+        IConfiguration configuration = Jellyfin.Server.Program.CreateAppConfiguration(new StartupOptions(), appPaths.Object);
+
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddTranscodeSessionStore(configuration, NullLogger.Instance);
+        services.AddQuickConnectStore(configuration, NullLogger.Instance);
+
+        return services.BuildServiceProvider();
+    }
+}

tests/Jellyfin.Server.Tests/QuickConnect/RedisQuickConnectStoreDegradedTests.cs

@@ -0,0 +1,308 @@
+using System;
+using System.Collections.Generic;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.QuickConnect;
+using Jellyfin.Server.Tests.HighAvailability;
+using MediaBrowser.Controller.Authentication;
+using MediaBrowser.Model.QuickConnect;
+using Microsoft.Extensions.Logging.Abstractions;
+using StackExchange.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Tests.QuickConnect;
+
+/// <summary>
+/// What a <see cref="RedisQuickConnectStore"/> does while its Redis is unreachable. Each instance talks
+/// to the one real server through a proxy of its own, so an outage can be given to one instance and not
+/// the others, and then taken back.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class RedisQuickConnectStoreDegradedTests : IAsyncLifetime
+{
+    private readonly List<RedisFaultProxy> _proxies = new();
+    private readonly List<IConnectionMultiplexer> _connections = new();
+
+    private RedisTestServer _redis = null!;
+
+    private static CancellationToken CancellationToken => TestContext.Current.CancellationToken;
+
+    /// <inheritdoc/>
+    public async ValueTask InitializeAsync()
+    {
+        _redis = await RedisTestServer.StartAsync().ConfigureAwait(false);
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask DisposeAsync()
+    {
+        foreach (var connection in _connections)
+        {
+            await connection.DisposeAsync().ConfigureAwait(false);
+        }
+
+        foreach (var proxy in _proxies)
+        {
+            await proxy.DisposeAsync().ConfigureAwait(false);
+        }
+
+        await _redis.DisposeAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// A request stored while Redis is unreachable is still resolvable on the instance that stored it,
+    /// so a flow whose three legs happen to land on one instance keeps working through the outage.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task PendingRequest_SurvivesAnOutage_OnTheInstanceThatStoredIt()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+
+        instance.Proxy.Cut();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+
+        Assert.Equal(request.Secret, (await instance.Store.GetRequestBySecretAsync(request.Secret, CancellationToken))?.Secret);
+        Assert.Equal(request.Secret, (await instance.Store.GetRequestByCodeAsync(request.Code, CancellationToken))?.Secret);
+    }
+
+    /// <summary>
+    /// Once Redis answers again it is the only authority: a miss is a miss, not a reason to serve the
+    /// copy this instance kept while it was unreachable.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task PendingRequest_StoredDuringAnOutage_IsNotServedOnceRedisAnswersAgain()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+
+        instance.Proxy.Cut();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+        Assert.NotNull(await instance.Store.GetRequestBySecretAsync(request.Secret, CancellationToken));
+
+        await RestoreAsync(instance);
+
+        Assert.Null(await instance.Store.GetRequestBySecretAsync(request.Secret, CancellationToken));
+        Assert.Null(await instance.Store.GetRequestByCodeAsync(request.Code, CancellationToken));
+    }
+
+    /// <summary>
+    /// A malformed stored value is a fault of its own, not a transport failure, so it is surfaced rather
+    /// than answered from the copy this instance happens to hold.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task PendingRequest_ThatIsMalformedInRedis_SurfacesInsteadOfDegrading()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+
+        instance.Proxy.Cut();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+        await RestoreAsync(instance);
+
+        await instance.Connection.GetDatabase().StringSetAsync(
+            "jellyfin:quickconnect:request:" + request.Secret,
+            "{ not json",
+            TimeSpan.FromMinutes(10));
+
+        await Assert.ThrowsAsync<JsonException>(() => instance.Store.GetRequestBySecretAsync(request.Secret, CancellationToken));
+    }
+
+    /// <summary>
+    /// An authorization write that failed leaves nothing behind on the instance, because the response
+    /// that never arrived may still have been applied and a second copy of an authorization is a second
+    /// access token.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Authorization_ThatFailedToStore_LeavesNothingOnTheInstance()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+
+        instance.Proxy.Cut();
+        await AssertTransportFailureAsync(() => instance.Store.SetAuthorizationAsync(
+            request.Secret,
+            new AuthenticationResult { AccessToken = "token-1" },
+            DateTime.UtcNow.AddMinutes(10),
+            CancellationToken));
+
+        await RestoreAsync(instance);
+
+        Assert.Null(await instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken));
+    }
+
+    /// <summary>
+    /// The instance whose authorization write failed while the write landed anyway still hands the token
+    /// out exactly once, rather than once from Redis and again from a copy of its own.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Authorization_IsHandedOutOnce_EvenAfterAFailedWriteOnTheSameInstance()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+        var authentication = new AuthenticationResult { AccessToken = "token-1" };
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+
+        instance.Proxy.Cut();
+        await AssertTransportFailureAsync(() => instance.Store.SetAuthorizationAsync(
+            request.Secret,
+            authentication,
+            DateTime.UtcNow.AddMinutes(10),
+            CancellationToken));
+
+        await RestoreAsync(instance);
+
+        // Stands in for that write having been applied before the response was lost.
+        await instance.Store.SetAuthorizationAsync(request.Secret, authentication, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+
+        Assert.Equal("token-1", (await instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken))?.AccessToken);
+        Assert.Null(await instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken));
+    }
+
+    /// <summary>
+    /// Exchanging during an outage fails loudly and spends nothing, so the token is still there to be
+    /// handed out once when Redis comes back.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Exchange_DuringAnOutage_SurfacesTheFailureAndLeavesTheTokenUnspent()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+        await instance.Store.SetAuthorizationAsync(
+            request.Secret,
+            new AuthenticationResult { AccessToken = "token-1" },
+            DateTime.UtcNow.AddMinutes(10),
+            CancellationToken);
+
+        instance.Proxy.Cut();
+        await AssertTransportFailureAsync(() => instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken));
+
+        await RestoreAsync(instance);
+
+        Assert.Equal("token-1", (await instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken))?.AccessToken);
+        Assert.Null(await instance.Store.TryConsumeAuthorizationAsync(request.Secret, CancellationToken));
+    }
+
+    /// <summary>
+    /// Authorizing during an outage fails loudly rather than claiming locally, because a claim only this
+    /// instance knows about does not stop another one minting a second access token.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Claim_DuringAnOutage_SurfacesTheFailure()
+    {
+        var instance = await CreateInstanceAsync();
+        var request = NewRequest();
+        await instance.Store.SetRequestAsync(request, DateTime.UtcNow.AddMinutes(10), CancellationToken);
+
+        instance.Proxy.Cut();
+        await AssertTransportFailureAsync(() => instance.Store.TryClaimAuthorizationAsync(
+            request.Secret,
+            DateTime.UtcNow.AddMinutes(10),
+            CancellationToken));
+    }
+
+    /// <summary>
+    /// Two instances racing to authorize one request: exactly one of them may go on to mint a token.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Claim_RacedOnTwoInstances_SucceedsOnce()
+    {
+        var first = await CreateInstanceAsync();
+        var second = await CreateInstanceAsync();
+
+        for (var attempt = 0; attempt < 25; attempt++)
+        {
+            var request = NewRequest();
+            var expiresUtc = DateTime.UtcNow.AddMinutes(10);
+            await first.Store.SetRequestAsync(request, expiresUtc, CancellationToken);
+
+            var claims = await Task.WhenAll(
+                Task.Run(() => first.Store.TryClaimAuthorizationAsync(request.Secret, expiresUtc, CancellationToken), CancellationToken),
+                Task.Run(() => second.Store.TryClaimAuthorizationAsync(request.Secret, expiresUtc, CancellationToken), CancellationToken));
+
+            Assert.Single(claims, claimed => claimed);
+        }
+    }
+
+    /// <summary>
+    /// A request that is unknown, already claimed or already authorized cannot be claimed.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Claim_IsRefused_ForUnknownClaimedAndAuthorizedRequests()
+    {
+        var instance = await CreateInstanceAsync();
+        var expiresUtc = DateTime.UtcNow.AddMinutes(10);
+
+        Assert.False(await instance.Store.TryClaimAuthorizationAsync("unknown-secret", expiresUtc, CancellationToken));
+
+        var request = NewRequest();
+        await instance.Store.SetRequestAsync(request, expiresUtc, CancellationToken);
+        Assert.True(await instance.Store.TryClaimAuthorizationAsync(request.Secret, expiresUtc, CancellationToken));
+        Assert.False(await instance.Store.TryClaimAuthorizationAsync(request.Secret, expiresUtc, CancellationToken));
+
+        var authorized = NewRequest();
+        authorized.Authenticated = true;
+        await instance.Store.SetRequestAsync(authorized, expiresUtc, CancellationToken);
+        Assert.False(await instance.Store.TryClaimAuthorizationAsync(authorized.Secret, expiresUtc, CancellationToken));
+    }
+
+    private static QuickConnectResult NewRequest() => new QuickConnectResult(
+        Guid.NewGuid().ToString("N"),
+        Guid.NewGuid().ToString("N").Substring(0, 6),
+        DateTime.UtcNow,
+        "device-1",
+        "Living Room TV",
+        "Jellyfin Web",
+        "1.0.0");
+
+    private static async Task AssertTransportFailureAsync(Func<Task> operation)
+    {
+        var exception = await Record.ExceptionAsync(operation);
+
+        Assert.NotNull(exception);
+        Assert.True(exception is RedisException or TimeoutException, exception.ToString());
+    }
+
+    private static async Task RestoreAsync(Instance instance)
+    {
+        instance.Proxy.Restore();
+
+        for (var attempt = 1; ; attempt++)
+        {
+            try
+            {
+                await instance.Connection.GetDatabase().PingAsync();
+                return;
+            }
+            catch (Exception exception) when (exception is RedisException or TimeoutException && attempt < 60)
+            {
+                await Task.Delay(TimeSpan.FromMilliseconds(500), CancellationToken);
+            }
+        }
+    }
+
+    private async Task<Instance> CreateInstanceAsync()
+    {
+        var proxy = RedisFaultProxy.Start(_redis.ConnectionString);
+        _proxies.Add(proxy);
+
+        var connection = await ConnectionMultiplexer.ConnectAsync(proxy.ConnectionString).ConfigureAwait(false);
+        _connections.Add(connection);
+
+        return new Instance(proxy, connection, new RedisQuickConnectStore(connection, NullLogger<RedisQuickConnectStore>.Instance));
+    }
+
+    private sealed record Instance(RedisFaultProxy Proxy, IConnectionMultiplexer Connection, RedisQuickConnectStore Store);
+}