feat(migration): Convert Compare-DbaAg* commands to C# binary cmdlets

Convert 6 Compare-DbaAg* PowerShell functions to C# binary cmdlets:
- Compare-DbaAgReplicaAgentJob
- Compare-DbaAgReplicaCredential
- Compare-DbaAgReplicaLogin
- Compare-DbaAgReplicaOperator
- Compare-DbaAgReplicaSync
- Compare-DbaAvailabilityGroup

Includes shared AgReplicaHelpers static class for common functionality
(GetAgReplicaInfoScript, property helpers, FindByName, error handling).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: potatoqualitee

dbatools.library.psd1

@@ -43,6 +43,12 @@
         'Add-DbaAgListener',
         'Add-DbaAgReplica',
         'Clear-DbaConnectionPool',
+        'Compare-DbaAgReplicaAgentJob',
+        'Compare-DbaAgReplicaCredential',
+        'Compare-DbaAgReplicaLogin',
+        'Compare-DbaAgReplicaOperator',
+        'Compare-DbaAgReplicaSync',
+        'Compare-DbaAvailabilityGroup',
         'Connect-DbaInstance',
         'Disable-DbaAgHadr',
         'Disconnect-DbaInstance',

project/dbatools/Commands/AgReplicaHelpers.cs

@@ -0,0 +1,140 @@
+using System;
+using System.Collections.Generic;
+using System.Management.Automation;
+
+namespace Dataplat.Dbatools.Commands
+{
+    /// <summary>
+    /// Shared utility methods and script blocks used by the Compare-DbaAgReplica* command family.
+    /// </summary>
+    internal static class AgReplicaHelpers
+    {
+        /// <summary>
+        /// Connects to an instance, validates HADR is enabled, and returns availability group
+        /// information including replica names. Throws sentinel strings for known error conditions.
+        /// </summary>
+        internal static readonly ScriptBlock GetAgReplicaInfoScript = ScriptBlock.Create(@"
+param($si, $sc, $hasCred, $agFilter, $hasAgFilter)
+$params = @{ SqlInstance = $si; MinimumVersion = 11 }
+if ($hasCred) { $params['SqlCredential'] = $sc }
+$server = Connect-DbaInstance @params
+if (-not $server.IsHadrEnabled) { throw 'HADR_NOT_ENABLED' }
+$ags = $server.AvailabilityGroups
+if ($hasAgFilter) { $ags = $ags | Where-Object Name -in $agFilter }
+if (-not $ags) { throw 'NO_AG_FOUND' }
+foreach ($ag in $ags) {
+    $replicaNames = @($ag.AvailabilityReplicas | ForEach-Object { $_.Name })
+    [PSCustomObject]@{ AgName = $ag.Name; ReplicaNames = $replicaNames }
+}
+");
+
+        /// <summary>
+        /// Gets a string property value from a PSObject.
+        /// </summary>
+        internal static string GetPropertyString(PSObject obj, string propertyName)
+        {
+            if (obj == null) return null;
+            try
+            {
+                PSPropertyInfo prop = obj.Properties[propertyName];
+                if (prop != null && prop.Value != null)
+                    return prop.Value.ToString();
+            }
+            catch (Exception)
+            {
+                // PSObject property access can throw for dynamic or computed properties
+            }
+            return null;
+        }
+
+        /// <summary>
+        /// Gets a property value (any type) from a PSObject.
+        /// </summary>
+        internal static object GetPropertyValue(PSObject obj, string propertyName)
+        {
+            if (obj == null) return null;
+            try
+            {
+                PSPropertyInfo prop = obj.Properties[propertyName];
+                if (prop != null) return prop.Value;
+            }
+            catch (Exception)
+            {
+                // PSObject property access can throw for dynamic or computed properties
+            }
+            return null;
+        }
+
+        /// <summary>
+        /// Gets a string array property from a PSObject, handling PowerShell array coercion.
+        /// </summary>
+        internal static string[] GetStringArray(PSObject obj, string propertyName)
+        {
+            if (obj == null) return null;
+            try
+            {
+                PSPropertyInfo prop = obj.Properties[propertyName];
+                if (prop == null || prop.Value == null) return null;
+
+                if (prop.Value is string[] strArray)
+                    return strArray;
+
+                if (prop.Value is object[] objArray)
+                {
+                    List<string> result = new List<string>();
+                    foreach (object item in objArray)
+                    {
+                        if (item != null)
+                        {
+                            if (item is PSObject pso)
+                                result.Add(pso.BaseObject != null ? pso.BaseObject.ToString() : pso.ToString());
+                            else
+                                result.Add(item.ToString());
+                        }
+                    }
+                    return result.ToArray();
+                }
+
+                return new string[] { prop.Value.ToString() };
+            }
+            catch (Exception)
+            {
+                // PSObject property access can throw for dynamic or computed properties
+            }
+            return null;
+        }
+
+        /// <summary>
+        /// Gets the full exception message chain including inner exceptions.
+        /// Used for sentinel string detection in errors thrown from embedded PowerShell scripts.
+        /// </summary>
+        internal static string GetFullExceptionMessage(Exception ex)
+        {
+            if (ex == null)
+                return "";
+            string msg = ex.Message ?? "";
+            Exception inner = ex.InnerException;
+            while (inner != null)
+            {
+                if (inner.Message != null)
+                    msg = msg + " " + inner.Message;
+                inner = inner.InnerException;
+            }
+            return msg;
+        }
+
+        /// <summary>
+        /// Finds a PSObject in a list by its Name property (case-insensitive).
+        /// </summary>
+        internal static PSObject FindByName(List<PSObject> items, string name)
+        {
+            foreach (PSObject item in items)
+            {
+                string itemName = GetPropertyString(item, "Name");
+                if (String.Equals(itemName, name, StringComparison.OrdinalIgnoreCase))
+                    return item;
+            }
+            return null;
+        }
+    }
+}