Auto: focas-f4d — password / unlock parameter

Closes #271

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FakeFocasClient.cs

@@ -40,6 +40,37 @@ internal class FakeFocasClient : IFocasClient
         return Task.CompletedTask;
     }
 
+    /// <summary>
+    ///     Plan PR F4-d (issue #271) — count of <see cref="UnlockAsync"/> invocations.
+    ///     Tests assert this to verify the driver routed <c>cnc_wrunlockparam</c> on
+    ///     connect when <c>FocasDeviceOptions.Password</c> was non-null and re-issued
+    ///     unlock on EW_PASSWD retry exactly once.
+    /// </summary>
+    public int UnlockCount { get; private set; }
+
+    /// <summary>
+    ///     Plan PR F4-d (issue #271) — last password observed by <see cref="UnlockAsync"/>.
+    ///     Used by the round-trip test to confirm the driver passed the configured
+    ///     password through unmodified. <b>This field exists ONLY in the fake — no
+    ///     production wire client retains the password past the wire call.</b>
+    /// </summary>
+    public string? LastUnlockPassword { get; private set; }
+
+    /// <summary>
+    ///     Plan PR F4-d (issue #271) — when set, <see cref="UnlockAsync"/> throws on
+    ///     invocation so tests can drive the failed-unlock retry path (where the
+    ///     driver surfaces BadUserAccessDenied as-is rather than retrying).
+    /// </summary>
+    public bool ThrowOnUnlock { get; set; }
+
+    public virtual Task UnlockAsync(string password, CancellationToken ct)
+    {
+        UnlockCount++;
+        LastUnlockPassword = password;
+        if (ThrowOnUnlock) throw Exception ?? new InvalidOperationException("Unlock fails");
+        return Task.CompletedTask;
+    }
+
     public virtual Task<(object? value, uint status)> ReadAsync(
         FocasAddress address, FocasDataType type, CancellationToken ct)
     {