Properly invalidate account caches when unlinking

PluralKit.Core/ProxyCache.cs

@@ -27,14 +27,19 @@ namespace PluralKit.Core
 
         public Task InvalidateSystem(PKSystem system) => InvalidateSystem(system.Id);
 
+        public void InvalidateAccounts(IEnumerable<ulong> accounts)
+        {
+            foreach (var account in accounts) 
+                _cache.Remove(KeyForAccount(account));
+        }
+
         public void InvalidateDeletedSystem(int systemId, IEnumerable<ulong> accounts)
         {
             // Used when the system's already removed so we can't look up accounts
             // We assume the account list is saved already somewhere and can be passed here (which is the case in Store)
             
             _cache.Remove(KeyForSystem(systemId));
-            foreach (var account in accounts) 
-                _cache.Remove(KeyForAccount(account));
+            InvalidateAccounts(accounts);
         }
 
         public async Task InvalidateSystem(int systemId)

PluralKit.Core/Stores.cs

@@ -509,6 +509,7 @@ namespace PluralKit {
 
             _logger.Information("Unlinked system {System} from account {Account}", system.Id, accountId);
             await _cache.InvalidateSystem(system);
+            _cache.InvalidateAccounts(new [] { accountId });
         }
 
         public async Task<PKSystem> GetSystemByAccount(ulong accountId) {