fix: re-implement the logic to use the existing links for other shows

but this time, make it off by default, with a setting to turn it on by default, and add a query parameter to each endpoint where it matter to override it as needed, if needed.

Shoko.Server/API/v3/Controllers/SeriesController.cs

@@ -1570,7 +1570,8 @@ public async Task<ActionResult> OverrideTMDBEpisodeMappingsBySeriesID(
     /// <param name="seriesID">Shoko Series ID.</param>
     /// <param name="tmdbShowID">The specified TMDB Show ID to search for links. This parameter is used to select a specific show.</param>
     /// <param name="tmdbSeasonID">The specified TMDB Season ID to search for links. If not provided, links are searched for any season of the selected or first linked show.</param>
-    /// <param name="keepExisting">Determines whether to retain any and all existing links.</param>
+    /// <param name="keepExisting">Determines whether to retain existing links when picking episodes.</param>
+    /// <param name="considerExistingOtherLinks">Determines whether to consider existing links for other series when picking episodes.</param>
     /// <param name="pageSize">The page size.</param>
     /// <param name="page">The page index.</param>
     /// <returns>A preview of the automagically matched episodes.</returns>
@@ -1581,6 +1582,7 @@ public async Task<ActionResult> OverrideTMDBEpisodeMappingsBySeriesID(
         [FromQuery] int? tmdbShowID,
         [FromQuery] int? tmdbSeasonID,
         [FromQuery] bool keepExisting = true,
+        [FromQuery] bool? considerExistingOtherLinks = null,
         [FromQuery, Range(0, 1000)] int pageSize = 50,
         [FromQuery, Range(1, int.MaxValue)] int page = 1
     )
@@ -1612,7 +1614,7 @@ public async Task<ActionResult> OverrideTMDBEpisodeMappingsBySeriesID(
                 return ValidationProblem("The selected tmdbSeasonID does not belong to the selected tmdbShowID", "tmdbSeasonID");
         }
 
-        return _tmdbLinkingService.MatchAnidbToTmdbEpisodes(series.AniDB_ID, tmdbShowID.Value, tmdbSeasonID, keepExisting, saveToDatabase: false)
+        return _tmdbLinkingService.MatchAnidbToTmdbEpisodes(series.AniDB_ID, tmdbShowID.Value, tmdbSeasonID, useExisting: keepExisting, useExistingOtherShows: considerExistingOtherLinks, saveToDatabase: false)
             .ToListResult(x => new TmdbEpisode.CrossReference(x), page, pageSize);
     }
 
@@ -1674,7 +1676,7 @@ public async Task<ActionResult> AutoTMDBEpisodeMappingsBySeriesID(
         if (isMissing)
             await _tmdbLinkingService.AddShowLink(series.AniDB_ID, body.TmdbShowID.Value, additiveLink: true);
         else
-            _tmdbLinkingService.MatchAnidbToTmdbEpisodes(series.AniDB_ID, body.TmdbShowID.Value, body.TmdbSeasonID, body.KeepExisting, saveToDatabase: true);
+            _tmdbLinkingService.MatchAnidbToTmdbEpisodes(series.AniDB_ID, body.TmdbShowID.Value, body.TmdbSeasonID, useExisting: body.KeepExisting, useExistingOtherShows: body.ConsiderExistingOtherLinks, saveToDatabase: true);
 
         if (tmdbShow.CreatedAt == tmdbShow.LastUpdatedAt)
         {

Shoko.Server/API/v3/Models/Shoko/Series.cs

@@ -711,10 +711,15 @@ public class AutoMatchTmdbEpisodesBody
             public int? TmdbSeasonID { get; set; }
 
             /// <summary>
-            /// Determines whether to retain any and all existing links.
+            /// Determines whether to retain existing links for the current series.
             /// </summary>
             [DefaultValue(true)]
             public bool KeepExisting { get; set; } = true;
+
+            /// <summary>
+            /// Determines whether to consider existing links for other series when picking episodes.
+            /// </summary>
+            public bool? ConsiderExistingOtherLinks { get; set; }
         }
 
         public class OverrideTmdbEpisodeMappingBody

Shoko.Server/Providers/TMDB/TmdbLinkingService.cs

@@ -14,6 +14,7 @@
 using Shoko.Server.Scheduling;
 using Shoko.Server.Scheduling.Jobs.TMDB;
 using Shoko.Server.Server;
+using Shoko.Server.Settings;
 using Shoko.Server.Utilities;
 
 using CrossRefSource = Shoko.Models.Enums.CrossRefSource;
@@ -32,6 +33,8 @@ public class TmdbLinkingService
 
     private readonly ISchedulerFactory _schedulerFactory;
 
+    private readonly ISettingsProvider _settingsProvider;
+
     private readonly TmdbImageService _imageService;
 
     private readonly AnimeSeriesRepository _animeSeries;
@@ -55,6 +58,7 @@ public class TmdbLinkingService
     public TmdbLinkingService(
         ILogger<TmdbLinkingService> logger,
         ISchedulerFactory schedulerFactory,
+        ISettingsProvider settingsProvider,
         TmdbImageService imageService,
         AnimeSeriesRepository animeSeries,
         AniDB_AnimeRepository anidbAnime,
@@ -69,6 +73,7 @@ CrossRef_AniDB_TMDB_EpisodeRepository xrefAnidbTmdbEpisodes
     {
         _logger = logger;
         _schedulerFactory = schedulerFactory;
+        _settingsProvider = settingsProvider;
         _imageService = imageService;
         _animeSeries = animeSeries;
         _anidbAnime = anidbAnime;
@@ -382,7 +387,7 @@ public bool SetEpisodeLink(int anidbEpisodeId, int tmdbEpisodeId, bool additiveL
         return true;
     }
 
-    public IReadOnlyList<CrossRef_AniDB_TMDB_Episode> MatchAnidbToTmdbEpisodes(int anidbAnimeId, int tmdbShowId, int? tmdbSeasonId, bool useExisting = false, bool saveToDatabase = false, bool useExistingOtherShows = true)
+    public IReadOnlyList<CrossRef_AniDB_TMDB_Episode> MatchAnidbToTmdbEpisodes(int anidbAnimeId, int tmdbShowId, int? tmdbSeasonId, bool useExisting = false, bool saveToDatabase = false, bool? useExistingOtherShows = null)
     {
         var anime = _anidbAnime.GetByAnimeID(anidbAnimeId);
         if (anime == null)
@@ -416,6 +421,21 @@ public IReadOnlyList<CrossRef_AniDB_TMDB_Episode> MatchAnidbToTmdbEpisodes(int a
         var tmdbEpisodes = tmdbEpisodeDict.Values
             .Where(episode => episode.SeasonNumber == 0 || !tmdbSeasonId.HasValue || episode.TmdbSeasonID == tmdbSeasonId.Value)
             .ToList();
+        var considerExistingOtherLinks = useExistingOtherShows ?? _settingsProvider.GetSettings().TMDB.ConsiderExistingOtherLinks;
+        if (considerExistingOtherLinks)
+        {
+            var otherShowsExisting = existing.Values.SelectMany(xref => xref).ExceptBy(anidbEpisodes.Keys.Append(0), xref => xref.AnidbEpisodeID).ToList();
+            foreach (var link in otherShowsExisting)
+            {
+                _logger.LogTrace("Skipping existing episode link: AniDB episode (EpisodeID={EpisodeID},AnimeID={AnimeID}) → TMDB episode (EpisodeID={TmdbID})", link.AnidbEpisodeID, link.AnidbAnimeID, link.TmdbEpisodeID);
+
+                // Exclude the linked episodes from the auto-match candidates.
+                var index = tmdbEpisodes.FindIndex(episode => episode.TmdbEpisodeID == link.TmdbEpisodeID);
+                if (index >= 0)
+                    tmdbEpisodes.RemoveAt(index);
+            }
+        }
+
         var tmdbNormalEpisodes = isOVA ? tmdbEpisodes : tmdbEpisodes
             .Where(episode => episode.SeasonNumber != 0)
             .OrderBy(episode => episode.SeasonNumber)

Shoko.Server/Settings/TMDBSettings.cs

@@ -23,6 +23,17 @@ public class TMDBSettings
     /// </summary>
     public bool AutoLinkRestricted { get; set; } = false;
 
+    /// <summary>
+    /// Determines whether to consider existing cross-reference links to other
+    /// AniDB anime when linking an AniDB anime to a TMDB show.
+    /// </summary>
+    /// <remarks>
+    /// This setting also applies to the auto-matching process and can be
+    /// overridden on a per request basis for the API when previewing or
+    /// linking.
+    /// </remarks>
+    public bool ConsiderExistingOtherLinks { get; set; } = false;
+
     /// <summary>
     /// Indicates that all titles should be stored locally for the TMDB entity,
     /// otherwise it will use