docs: backfill XML documentation across 756 files

Adds <summary>, <param>, <typeparam>, and <inheritdoc/> tags to public
members surfaced by commentchecker — resolves 5,847 of 5,869 issues
(99.6%) across three /fixdocs passes.

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/OpcUaApplicationHostImpersonationTests.cs

@@ -17,6 +17,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
     private static readonly UserTokenPolicy UserNamePolicy = new(UserTokenType.UserName) { PolicyId = "username_basic256sha256" };
     private static readonly UserTokenPolicy AnonPolicy = new(UserTokenType.Anonymous) { PolicyId = "anonymous" };
 
+    /// <summary>Verifies successful UserName token impersonation sets identity and clears validation error.</summary>
     [Fact]
     public void HandleImpersonation_username_success_sets_identity_and_no_validation_error()
     {
@@ -33,6 +34,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
         authenticator.LastPassword.ShouldBe("secret");
     }
 
+    /// <summary>Verifies failed UserName token impersonation sets validation error and clears identity.</summary>
     [Fact]
     public void HandleImpersonation_username_denial_sets_validation_error_and_no_identity()
     {
@@ -47,6 +49,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
         args.IdentityValidationError.LocalizedText.Text.ShouldContain("Invalid credentials");
     }
 
+    /// <summary>Verifies anonymous identity tokens are passed through to the SDK default handler.</summary>
     [Fact]
     public void HandleImpersonation_anonymous_token_falls_through_to_sdk_default()
     {
@@ -61,6 +64,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
         authenticator.LastUsername.ShouldBeNull("anonymous tokens must not hit the authenticator");
     }
 
+    /// <summary>Verifies authenticator exceptions result in rejection with validation error.</summary>
     [Fact]
     public void HandleImpersonation_authenticator_throwing_results_in_rejection()
     {
@@ -74,6 +78,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
         args.IdentityValidationError.Code.ShouldBe(StatusCodes.BadIdentityTokenRejected);
     }
 
+    /// <summary>Verifies null username is normalized to empty string before authenticator call.</summary>
     [Fact]
     public void HandleImpersonation_null_username_treated_as_empty_string()
     {
@@ -86,6 +91,7 @@ public sealed class OpcUaApplicationHostImpersonationTests
         authenticator.LastUsername.ShouldBe(string.Empty);
     }
 
+    /// <summary>Verifies NullOpcUaUserAuthenticator always returns denial result.</summary>
     [Fact]
     public async Task NullOpcUaUserAuthenticator_always_denies()
     {
@@ -99,9 +105,16 @@ public sealed class OpcUaApplicationHostImpersonationTests
 
     private sealed class RecordingAuthenticator(OpcUaUserAuthResult outcome) : IOpcUaUserAuthenticator
     {
+        /// <summary>Gets the username passed to the last authentication call.</summary>
         public string? LastUsername { get; private set; }
+        /// <summary>Gets the password passed to the last authentication call.</summary>
         public string? LastPassword { get; private set; }
 
+        /// <summary>Authenticates a username and password, recording them for inspection by tests.</summary>
+        /// <param name="username">The username to authenticate.</param>
+        /// <param name="password">The password to authenticate.</param>
+        /// <param name="ct">The cancellation token.</param>
+        /// <returns>The predefined authentication result.</returns>
         public Task<OpcUaUserAuthResult> AuthenticateUserNameAsync(string username, string password, CancellationToken ct)
         {
             LastUsername = username;
@@ -110,8 +123,14 @@ public sealed class OpcUaApplicationHostImpersonationTests
         }
     }
 
+    /// <summary>Test authenticator that throws an exception during authentication.</summary>
     private sealed class ThrowingAuthenticator(Exception ex) : IOpcUaUserAuthenticator
     {
+        /// <summary>Authenticates by throwing the configured exception.</summary>
+        /// <param name="username">The username to authenticate.</param>
+        /// <param name="password">The password to authenticate.</param>
+        /// <param name="ct">The cancellation token.</param>
+        /// <returns>Never returns; always throws the configured exception.</returns>
         public Task<OpcUaUserAuthResult> AuthenticateUserNameAsync(string username, string password, CancellationToken ct)
             => Task.FromException<OpcUaUserAuthResult>(ex);
     }