Attempt to have a minute grace whenever collection get removed.

LightlessSync/PlayerData/Pairs/PairHandlerRegistry.cs

@@ -11,7 +11,9 @@ public sealed class PairHandlerRegistry : IDisposable
 {
     private readonly object _gate = new();
     private readonly object _pendingGate = new();
+    private readonly object _visibilityGate = new();
     private readonly Dictionary<string, PairHandlerEntry> _entriesByIdent = new(StringComparer.Ordinal);
+    private readonly Dictionary<string, CancellationTokenSource> _pendingInvisibleEvictions = new(StringComparer.Ordinal);
     private readonly Dictionary<IPairHandlerAdapter, PairHandlerEntry> _entriesByHandler = new(ReferenceEqualityComparer.Instance);
 
     private readonly IPairHandlerAdapterFactory _handlerFactory;
@@ -144,6 +146,37 @@ public sealed class PairHandlerRegistry : IDisposable
         return PairOperationResult<PairUniqueIdentifier>.Ok(registration.PairIdent);
     }
 
+    private PairOperationResult CancelAllInvisibleEvictions()
+    {
+        List<CancellationTokenSource> snapshot;
+        lock (_visibilityGate)
+        {
+            snapshot = [.. _pendingInvisibleEvictions.Values];
+            _pendingInvisibleEvictions.Clear();
+        }
+
+        List<string>? errors = null;
+
+        foreach (var cts in snapshot)
+        {
+            try { cts.Cancel(); }
+            catch (Exception ex)
+            {
+                (errors ??= new List<string>()).Add($"Cancel: {ex.Message}");
+            }
+
+            try { cts.Dispose(); }
+            catch (Exception ex)
+            {
+                (errors ??= new List<string>()).Add($"Dispose: {ex.Message}");
+            }
+        }
+
+        return errors is null
+            ? PairOperationResult.Ok()
+            : PairOperationResult.Fail($"CancelAllInvisibleEvictions had error(s): {string.Join(" | ", errors)}");
+    }
+
     public PairOperationResult ApplyCharacterData(PairRegistration registration, OnlineUserCharaDataDto dto)
     {
         if (registration.CharacterIdent is null)
@@ -300,6 +333,7 @@ public sealed class PairHandlerRegistry : IDisposable
         lock (_gate)
         {
             handlers = _entriesByHandler.Keys.ToList();
+            CancelAllInvisibleEvictions();
             _entriesByIdent.Clear();
             _entriesByHandler.Clear();
         }
@@ -332,6 +366,7 @@ public sealed class PairHandlerRegistry : IDisposable
         lock (_gate)
         {
             handlers = _entriesByHandler.Keys.ToList();
+            CancelAllInvisibleEvictions();
             _entriesByIdent.Clear();
             _entriesByHandler.Clear();
         }