test: fix tests to match new expectations that Auth and Unlock data need to have the same data.

src/Core/Utilities/KdfSettingsValidator.cs

@@ -24,10 +24,11 @@ public static class KdfSettingsValidator
             yield break;
         }
 
+        // Salt must be equal for authentication and unlock to prevent de-synced salt value
         if (authentication.Salt != unlock.Salt)
         {
             yield return new ValidationResult(
-                "Salt must be equal for authentication and unlock.",
+                "Invalid master password salt.",
                 [nameof(authentication.Salt)]);
         }
 

test/Api.Test/Auth/Models/Request/Accounts/PasswordRequestModelTests.cs

@@ -122,7 +122,7 @@ public class PasswordRequestModelTests
         var result = model.Validate(new ValidationContext(model)).ToList();
 
         // Assert
-        Assert.Contains(result, r => r.ErrorMessage != null && r.ErrorMessage.Contains("Salt must be equal"));
+        Assert.Contains(result, r => r.ErrorMessage != null && r.ErrorMessage.Contains("Invalid master password salt."));
     }
 
     [Fact]
@@ -163,31 +163,6 @@ public class PasswordRequestModelTests
 
     #endregion
 
-    #region Both-or-Neither Tests
-
-    /// <summary>
-    /// This test proves backwards compatibility for clients that don't send either AuthenticationData or UnlockData
-    /// </summary>
-    [Fact]
-    public void Validate_WhenBothNull_NoAuthUnlockErrors()
-    {
-        // Arrange
-        var model = new PasswordRequestModel
-        {
-            MasterPasswordHash = "masterPasswordHash",
-            NewMasterPasswordHash = "newHash",
-            Key = "key",
-            AuthenticationData = null,
-            UnlockData = null
-        };
-
-        // Act
-        var result = model.Validate(new ValidationContext(model)).ToList();
-
-        // Assert — no auth/unlock-related errors
-        Assert.Empty(result);
-    }
-
     [Fact]
     public void Validate_WhenOnlyAuthPresent_ReturnsError()
     {
@@ -246,8 +221,6 @@ public class PasswordRequestModelTests
         Assert.Contains(result, r => r.ErrorMessage != null && r.ErrorMessage.Contains(nameof(PasswordRequestModel.AuthenticationData)));
     }
 
-    #endregion
-
     #region Base Validation Preserved
 
     [Fact]

test/Identity.Test/Controllers/AccountsControllerTests.cs

@@ -953,8 +953,9 @@ public class AccountsControllerTests : IDisposable
         // Act
         var results = model.Validate(ctx).ToList();
 
-        // Assert mismatched auth/unlock is allowed
-        Assert.Empty(results);
+        // Assert mismatched auth/unlock KDF settings are rejected
+        Assert.Single(results);
+        Assert.Equal("KDF settings must be equal for authentication and unlock.", results[0].ErrorMessage);
     }
 
     [Theory, BitAutoData]
@@ -1004,8 +1005,9 @@ public class AccountsControllerTests : IDisposable
         // Act
         var results = model.Validate(ctx).ToList();
 
-        // Assert mismatched salts between auth/unlock are allowed
-        Assert.Empty(results);
+        // Assert mismatched salts between auth/unlock are rejected
+        Assert.Single(results);
+        Assert.Equal("Invalid master password salt.", results[0].ErrorMessage);
     }
 
     [Theory, BitAutoData]