Include variable declarations for batch enlistment and add new endpoint hooks in validation.

Author: carcer

src/Http/Wolverine.Http.Tests/Marten/reacting_to_read_aggregate.cs

@@ -124,6 +124,8 @@ await theHost.Scenario(x =>
 
 public static class LetterAggregateEndpointWithValidation
 {
+    public static void Before(Guid id) { }
+
     public static ProblemDetails Validate(LetterAggregate letters)
     {
         if (letters.ACount is 0)
@@ -142,6 +144,8 @@ public static LetterAggregate PostLetter([WriteAggregate(Required = true, OnMiss
 
 public static class LetterAggregateEndpoint
 {
+    public static void Load(Guid id) { }
+
     #region sample_read_aggregate_fine_grained_validation_control
 
     // Straight up 404 on missing

src/Persistence/Wolverine.Marten/Codegen/MartenQueryingFrame.cs

@@ -107,5 +107,17 @@ public override IEnumerable<Variable> FindVariables(IMethodVariables chain)
 
         _cancellation = chain.FindVariable(typeof(CancellationToken));
         yield return _cancellation;
+
+        // This ensures those variables are declared before we try to use them in the batch enlistment code
+        foreach (var op in _operations)
+        {
+            if (op is Frame frame)
+            {
+                foreach (var variable in frame.FindVariables(chain))
+                {
+                    yield return variable;
+                }
+            }
+        }
     }
 }