Desktop: let a lock pressed during an unlock win, instead of the unlock finishing behind it

tests/DodoSSH.Client.Session.Tests/FakeDeviceKeyStore.cs

@@ -25,8 +25,18 @@ internal sealed class FakeDeviceKeyStore : IDeviceKeyStore
     internal void Overwrite(byte[] replacement) => key = replacement;
 
     /// <inheritdoc />
-    public ValueTask<bool> IsAvailableAsync(CancellationToken cancellationToken) =>
-        ValueTask.FromResult(IsAvailable);
+    public async ValueTask<bool> IsAvailableAsync(CancellationToken cancellationToken)
+    {
+        if (HoldAvailability is { } hold)
+        {
+            await hold.WaitAsync(cancellationToken).ConfigureAwait(false);
+        }
+
+        return IsAvailable;
+    }
+
+    /// <summary>When set, availability is not answered until it completes: an unlock held part-way.</summary>
+    internal Task? HoldAvailability { get; set; }
 
     /// <inheritdoc />
     public ValueTask SaveAsync(ReadOnlyMemory<byte> devicePrivateKey, CancellationToken cancellationToken)