Fix parser comparison mismatches (#4220)

src/Runner.Worker/ActionManifestManagerWrapper.cs

@@ -84,7 +84,8 @@ namespace GitHub.Runner.Worker
                 "EvaluateContainerEnvironment",
                 () => _legacyManager.EvaluateContainerEnvironment(executionContext, token, extraExpressionValues),
                 () => _newManager.EvaluateContainerEnvironment(executionContext, ConvertToNewToken(token) as GitHub.Actions.WorkflowParser.ObjectTemplating.Tokens.MappingToken, ConvertToNewExpressionValues(extraExpressionValues)),
-                (legacyResult, newResult) => {
+                (legacyResult, newResult) =>
+                {
                     var trace = HostContext.GetTrace(nameof(ActionManifestManagerWrapper));
                     return CompareDictionaries(trace, legacyResult, newResult, "ContainerEnvironment");
                 });
@@ -165,9 +166,150 @@ namespace GitHub.Runner.Worker
                 return null;
             }
 
-            // Serialize new steps and deserialize to old steps
-            var json = StringUtil.ConvertToJson(newSteps, Newtonsoft.Json.Formatting.None);
-            return StringUtil.ConvertFromJson<List<GitHub.DistributedTask.Pipelines.ActionStep>>(json);
+            var result = new List<GitHub.DistributedTask.Pipelines.ActionStep>();
+            foreach (var step in newSteps)
+            {
+                var actionStep = new GitHub.DistributedTask.Pipelines.ActionStep
+                {
+                    ContextName = step.Id,
+                };
+
+                if (step is GitHub.Actions.WorkflowParser.RunStep runStep)
+                {
+                    actionStep.Condition = ExtractConditionString(runStep.If);
+                    actionStep.DisplayNameToken = ConvertToLegacyToken<TemplateToken>(runStep.Name);
+                    actionStep.ContinueOnError = ConvertToLegacyToken<TemplateToken>(runStep.ContinueOnError);
+                    actionStep.TimeoutInMinutes = ConvertToLegacyToken<TemplateToken>(runStep.TimeoutMinutes);
+                    actionStep.Environment = ConvertToLegacyToken<TemplateToken>(runStep.Env);
+                    actionStep.Reference = new GitHub.DistributedTask.Pipelines.ScriptReference();
+                    actionStep.Inputs = BuildRunStepInputs(runStep);
+                }
+                else if (step is GitHub.Actions.WorkflowParser.ActionStep usesStep)
+                {
+                    actionStep.Condition = ExtractConditionString(usesStep.If);
+                    actionStep.DisplayNameToken = ConvertToLegacyToken<TemplateToken>(usesStep.Name);
+                    actionStep.ContinueOnError = ConvertToLegacyToken<TemplateToken>(usesStep.ContinueOnError);
+                    actionStep.TimeoutInMinutes = ConvertToLegacyToken<TemplateToken>(usesStep.TimeoutMinutes);
+                    actionStep.Environment = ConvertToLegacyToken<TemplateToken>(usesStep.Env);
+                    actionStep.Reference = ParseActionReference(usesStep.Uses?.Value);
+                    actionStep.Inputs = ConvertToLegacyToken<MappingToken>(usesStep.With);
+                }
+
+                result.Add(actionStep);
+            }
+            return result;
+        }
+
+        private string ExtractConditionString(GitHub.Actions.WorkflowParser.ObjectTemplating.Tokens.BasicExpressionToken ifToken)
+        {
+            if (ifToken == null)
+            {
+                return null;
+            }
+
+            // The Expression property is internal, so we use ToString() which formats as "${{ expr }}"
+            // Then strip the delimiters to get just the expression
+            var str = ifToken.ToString();
+            if (str.StartsWith("${{") && str.EndsWith("}}"))
+            {
+                return str.Substring(3, str.Length - 5).Trim();
+            }
+            return str;
+        }
+
+        private MappingToken BuildRunStepInputs(GitHub.Actions.WorkflowParser.RunStep runStep)
+        {
+            var inputs = new MappingToken(null, null, null);
+
+            // script (from run)
+            if (runStep.Run != null)
+            {
+                inputs.Add(
+                    new StringToken(null, null, null, "script"),
+                    ConvertToLegacyToken<TemplateToken>(runStep.Run));
+            }
+
+            // shell
+            if (runStep.Shell != null)
+            {
+                inputs.Add(
+                    new StringToken(null, null, null, "shell"),
+                    ConvertToLegacyToken<TemplateToken>(runStep.Shell));
+            }
+
+            // working-directory
+            if (runStep.WorkingDirectory != null)
+            {
+                inputs.Add(
+                    new StringToken(null, null, null, "workingDirectory"),
+                    ConvertToLegacyToken<TemplateToken>(runStep.WorkingDirectory));
+            }
+
+            return inputs.Count > 0 ? inputs : null;
+        }
+
+        private GitHub.DistributedTask.Pipelines.ActionStepDefinitionReference ParseActionReference(string uses)
+        {
+            if (string.IsNullOrEmpty(uses))
+            {
+                return null;
+            }
+
+            // Docker reference: docker://image:tag
+            if (uses.StartsWith("docker://", StringComparison.OrdinalIgnoreCase))
+            {
+                return new GitHub.DistributedTask.Pipelines.ContainerRegistryReference
+                {
+                    Image = uses.Substring("docker://".Length)
+                };
+            }
+
+            // Local path reference: ./path/to/action
+            if (uses.StartsWith("./") || uses.StartsWith(".\\"))
+            {
+                return new GitHub.DistributedTask.Pipelines.RepositoryPathReference
+                {
+                    RepositoryType = "self",
+                    Path = uses
+                };
+            }
+
+            // Repository reference: owner/repo@ref or owner/repo/path@ref
+            var atIndex = uses.LastIndexOf('@');
+            string refPart = null;
+            string repoPart = uses;
+
+            if (atIndex > 0)
+            {
+                refPart = uses.Substring(atIndex + 1);
+                repoPart = uses.Substring(0, atIndex);
+            }
+
+            // Split by / to get owner/repo and optional path
+            var parts = repoPart.Split('/');
+            string name;
+            string path = null;
+
+            if (parts.Length >= 2)
+            {
+                name = $"{parts[0]}/{parts[1]}";
+                if (parts.Length > 2)
+                {
+                    path = string.Join("/", parts, 2, parts.Length - 2);
+                }
+            }
+            else
+            {
+                name = repoPart;
+            }
+
+            return new GitHub.DistributedTask.Pipelines.RepositoryPathReference
+            {
+                RepositoryType = "GitHub",
+                Name = name,
+                Ref = refPart,
+                Path = path
+            };
         }
 
         private T ConvertToLegacyToken<T>(GitHub.Actions.WorkflowParser.ObjectTemplating.Tokens.TemplateToken newToken) where T : TemplateToken
@@ -633,6 +775,14 @@ namespace GitHub.Runner.Worker
                 return false;
             }
 
+            // Check for known equivalent error patterns (e.g., JSON parse errors)
+            // where both parsers correctly reject invalid input but with different wording
+            if (PipelineTemplateEvaluatorWrapper.HasJsonExceptionType(legacyException) && PipelineTemplateEvaluatorWrapper.HasJsonExceptionType(newException))
+            {
+                trace.Info("CompareExceptions - both exceptions are JSON parse errors, treating as matched");
+                return true;
+            }
+
             // Compare exception messages recursively (including inner exceptions)
             var legacyMessages = GetExceptionMessages(legacyException);
             var newMessages = GetExceptionMessages(newException);
@@ -697,5 +847,6 @@ namespace GitHub.Runner.Worker
 
             return messages;
         }
+
     }
 }

src/Runner.Worker/InternalsVisibleTo.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("Test")]

src/Runner.Worker/PipelineTemplateEvaluatorWrapper.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using GitHub.Actions.WorkflowParser;
 using GitHub.DistributedTask.Expressions2;
@@ -216,12 +216,15 @@ namespace GitHub.Runner.Worker
             }
         }
 
-        private TLegacy EvaluateAndCompare<TLegacy, TNew>(
+        internal TLegacy EvaluateAndCompare<TLegacy, TNew>(
             string methodName,
             Func<TLegacy> legacyEvaluator,
             Func<TNew> newEvaluator,
             Func<TLegacy, TNew, bool> resultComparer)
         {
+            // Capture cancellation state before evaluation
+            var cancellationRequestedBefore = _context.CancellationToken.IsCancellationRequested;
+
             // Legacy evaluator
             var legacyException = default(Exception);
             var legacyResult = default(TLegacy);
@@ -253,14 +256,18 @@ namespace GitHub.Runner.Worker
                     newException = ex;
                 }
 
+                // Capture cancellation state after evaluation
+                var cancellationRequestedAfter = _context.CancellationToken.IsCancellationRequested;
+
                 // Compare results or exceptions
+                bool hasMismatch = false;
                 if (legacyException != null || newException != null)
                 {
                     // Either one or both threw exceptions - compare them
                     if (!CompareExceptions(legacyException, newException))
                     {
                         _trace.Info($"{methodName} exception mismatch");
-                        RecordMismatch($"{methodName}");
+                        hasMismatch = true;
                     }
                 }
                 else
@@ -269,6 +276,20 @@ namespace GitHub.Runner.Worker
                     if (!resultComparer(legacyResult, newResult))
                     {
                         _trace.Info($"{methodName} mismatch");
+                        hasMismatch = true;
+                    }
+                }
+
+                // Only record mismatch if it wasn't caused by a cancellation race condition
+                if (hasMismatch)
+                {
+                    if (!cancellationRequestedBefore && cancellationRequestedAfter)
+                    {
+                        // Cancellation state changed during evaluation window - skip recording
+                        _trace.Info($"{methodName} mismatch skipped due to cancellation race condition");
+                    }
+                    else
+                    {
                         RecordMismatch($"{methodName}");
                     }
                 }
@@ -612,6 +633,13 @@ namespace GitHub.Runner.Worker
                 return false;
             }
 
+            // Check for known equivalent error patterns (e.g., JSON parse errors)
+            // where both parsers correctly reject invalid input but with different wording
+            if (IsKnownEquivalentErrorPattern(legacyException, newException))
+            {
+                return true;
+            }
+
             // Compare exception messages recursively (including inner exceptions)
             var legacyMessages = GetExceptionMessages(legacyException);
             var newMessages = GetExceptionMessages(newException);
@@ -634,6 +662,67 @@ namespace GitHub.Runner.Worker
             return true;
         }
 
+        /// <summary>
+        /// Checks if two exceptions match a known pattern where both parsers correctly reject
+        /// invalid input but with different error messages (e.g., JSON parse errors from fromJSON).
+        /// </summary>
+        private bool IsKnownEquivalentErrorPattern(Exception legacyException, Exception newException)
+        {
+            // fromJSON('') - both parsers fail when parsing empty string as JSON
+            // The error messages differ but both indicate JSON parsing failure.
+            // Legacy throws raw JsonReaderException: "Error reading JToken from JsonReader..."
+            // New wraps it: "Error parsing fromJson" with inner JsonReaderException
+            // Both may be wrapped in TemplateValidationException: "The template is not valid..."
+            if (HasJsonExceptionType(legacyException) && HasJsonExceptionType(newException))
+            {
+                _trace.Info("CompareExceptions - both exceptions are JSON parse errors, treating as matched");
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Checks if the exception chain contains a JSON-related exception type.
+        /// </summary>
+        internal static bool HasJsonExceptionType(Exception ex)
+        {
+            var toProcess = new Queue<Exception>();
+            toProcess.Enqueue(ex);
+            int count = 0;
+
+            while (toProcess.Count > 0 && count < 50)
+            {
+                var current = toProcess.Dequeue();
+                if (current == null) continue;
+
+                count++;
+
+                if (current is Newtonsoft.Json.JsonReaderException ||
+                    current is System.Text.Json.JsonException)
+                {
+                    return true;
+                }
+
+                if (current is AggregateException aggregateEx)
+                {
+                    foreach (var innerEx in aggregateEx.InnerExceptions)
+                    {
+                        if (innerEx != null && count < 50)
+                        {
+                            toProcess.Enqueue(innerEx);
+                        }
+                    }
+                }
+                else if (current.InnerException != null)
+                {
+                    toProcess.Enqueue(current.InnerException);
+                }
+            }
+
+            return false;
+        }
+
         private IList<string> GetExceptionMessages(Exception ex)
         {
             var messages = new List<string>();

src/Sdk/WorkflowParser/Conversion/WorkflowTemplateConverter.cs

@@ -1,4 +1,4 @@
-#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
+#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
 
 using System;
 using System.Collections.Generic;
@@ -43,7 +43,7 @@ namespace GitHub.Actions.WorkflowParser.Conversion
                     {
                         case WorkflowTemplateConstants.On:
                             var inputTypes = ConvertToOnWorkflowDispatchInputTypes(workflowPair.Value);
-                            foreach(var item in inputTypes)
+                            foreach (var item in inputTypes)
                             {
                                 result.InputTypes.TryAdd(item.Key, item.Value);
                             }
@@ -432,7 +432,7 @@ namespace GitHub.Actions.WorkflowParser.Conversion
                 context.Error(snapshotToken, $"job {WorkflowTemplateConstants.Snapshot} {WorkflowTemplateConstants.ImageName} is required.");
                 return null;
             }
-            
+
             return new Snapshot
             {
                 ImageName = imageName,
@@ -445,7 +445,7 @@ namespace GitHub.Actions.WorkflowParser.Conversion
         {
             var versionSegments = versionString.Split(".");
 
-            if (versionSegments.Length != 2 || 
+            if (versionSegments.Length != 2 ||
                 !versionSegments[1].Equals("*") ||
                 !Int32.TryParse(versionSegments[0], NumberStyles.None, CultureInfo.InvariantCulture, result: out int parsedMajor) ||
                 parsedMajor < 0)
@@ -1154,7 +1154,12 @@ namespace GitHub.Actions.WorkflowParser.Conversion
 
             if (String.IsNullOrEmpty(result.Image))
             {
-                context.Error(value, "Container image cannot be empty");
+                // Only error during early validation (parse time)
+                // At runtime (expression evaluation), empty image = no container
+                if (isEarlyValidation)
+                {
+                    context.Error(value, "Container image cannot be empty");
+                }
                 return null;
             }
 
@@ -1838,9 +1843,9 @@ namespace GitHub.Actions.WorkflowParser.Conversion
                     case "actions":
                         permissions.Actions = permissionLevel;
                         break;
-					case "artifact-metadata":
-						permissions.ArtifactMetadata = permissionLevel;
-						break;
+                    case "artifact-metadata":
+                        permissions.ArtifactMetadata = permissionLevel;
+                        break;
                     case "attestations":
                         permissions.Attestations = permissionLevel;
                         break;

src/Test/L0/Worker/ActionManifestParserComparisonL0.cs

@@ -0,0 +1,424 @@
+using GitHub.Actions.WorkflowParser;
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.DistributedTask.Pipelines.ContextData;
+using GitHub.DistributedTask.Pipelines.ObjectTemplating;
+using GitHub.DistributedTask.WebApi;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+using GitHub.Runner.Worker;
+using LegacyContextData = GitHub.DistributedTask.Pipelines.ContextData;
+using LegacyExpressions = GitHub.DistributedTask.Expressions2;
+using Moq;
+using Newtonsoft.Json;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Xunit;
+
+namespace GitHub.Runner.Common.Tests.Worker
+{
+    /// <summary>
+    /// Tests for parser comparison wrapper classes.
+    /// </summary>
+    public sealed class ActionManifestParserComparisonL0
+    {
+        private CancellationTokenSource _ecTokenSource;
+        private Mock<IExecutionContext> _ec;
+        private TestHostContext _hc;
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void ConvertToLegacySteps_ProducesCorrectSteps_WithExplicitPropertyMapping()
+        {
+            try
+            {
+                // Arrange - Test that ActionManifestManagerWrapper properly converts new steps to legacy format
+                Setup();
+
+                // Enable comparison feature
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                // Register required services
+                var legacyManager = new ActionManifestManagerLegacy();
+                legacyManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManagerLegacy>(legacyManager);
+
+                var newManager = new ActionManifestManager();
+                newManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManager>(newManager);
+
+                var wrapper = new ActionManifestManagerWrapper();
+                wrapper.Initialize(_hc);
+
+                var manifestPath = Path.Combine(TestUtil.GetTestDataPath(), "conditional_composite_action.yml");
+
+                // Act - Load through the wrapper (which internally converts)
+                var result = wrapper.Load(_ec.Object, manifestPath);
+
+                // Assert
+                Assert.NotNull(result);
+                Assert.Equal(ActionExecutionType.Composite, result.Execution.ExecutionType);
+
+                var compositeExecution = result.Execution as CompositeActionExecutionData;
+                Assert.NotNull(compositeExecution);
+                Assert.NotNull(compositeExecution.Steps);
+                Assert.Equal(6, compositeExecution.Steps.Count);
+
+                // Verify steps are NOT null (this was the bug - JSON round-trip produced nulls)
+                foreach (var step in compositeExecution.Steps)
+                {
+                    Assert.NotNull(step);
+                    Assert.NotNull(step.Reference);
+                    Assert.IsType<GitHub.DistributedTask.Pipelines.ScriptReference>(step.Reference);
+                }
+
+                // Verify step with condition
+                var successStep = compositeExecution.Steps[2];
+                Assert.Equal("success-conditional", successStep.ContextName);
+                Assert.Equal("success()", successStep.Condition);
+
+                // Verify step with complex condition
+                var lastStep = compositeExecution.Steps[5];
+                Assert.Contains("inputs.exit-code == 1", lastStep.Condition);
+                Assert.Contains("failure()", lastStep.Condition);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobContainer_EmptyImage_BothParsersReturnNull()
+        {
+            try
+            {
+                // Arrange - Test that both parsers return null for empty container image at runtime
+                Setup();
+
+                var fileTable = new List<string>();
+
+                // Create legacy evaluator
+                var legacyTraceWriter = new GitHub.DistributedTask.ObjectTemplating.EmptyTraceWriter();
+                var schema = PipelineTemplateSchemaFactory.GetSchema();
+                var legacyEvaluator = new PipelineTemplateEvaluator(legacyTraceWriter, schema, fileTable);
+
+                // Create new evaluator
+                var newTraceWriter = new GitHub.Actions.WorkflowParser.ObjectTemplating.EmptyTraceWriter();
+                var newEvaluator = new WorkflowTemplateEvaluator(newTraceWriter, fileTable, features: null);
+
+                // Create a token representing an empty container image (simulates expression evaluated to empty string)
+                var emptyImageToken = new StringToken(null, null, null, "");
+
+                var contextData = new DictionaryContextData();
+                var expressionFunctions = new List<LegacyExpressions.IFunctionInfo>();
+
+                // Act - Call both evaluators
+                var legacyResult = legacyEvaluator.EvaluateJobContainer(emptyImageToken, contextData, expressionFunctions);
+
+                // Convert token for new evaluator
+                var newToken = new GitHub.Actions.WorkflowParser.ObjectTemplating.Tokens.StringToken(null, null, null, "");
+                var newContextData = new GitHub.Actions.Expressions.Data.DictionaryExpressionData();
+                var newExpressionFunctions = new List<GitHub.Actions.Expressions.IFunctionInfo>();
+
+                var newResult = newEvaluator.EvaluateJobContainer(newToken, newContextData, newExpressionFunctions);
+
+                // Assert - Both should return null for empty image (no container)
+                Assert.Null(legacyResult);
+                Assert.Null(newResult);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void FromJsonEmptyString_BothParsersFail_WithDifferentMessages()
+        {
+            // This test verifies that both parsers fail with different error messages when parsing fromJSON('')
+            // The comparison layer should treat these as semantically equivalent (both are JSON parse errors)
+            try
+            {
+                Setup();
+
+                var fileTable = new List<string>();
+
+                // Create legacy evaluator
+                var legacyTraceWriter = new GitHub.DistributedTask.ObjectTemplating.EmptyTraceWriter();
+                var schema = PipelineTemplateSchemaFactory.GetSchema();
+                var legacyEvaluator = new PipelineTemplateEvaluator(legacyTraceWriter, schema, fileTable);
+
+                // Create new evaluator
+                var newTraceWriter = new GitHub.Actions.WorkflowParser.ObjectTemplating.EmptyTraceWriter();
+                var newEvaluator = new WorkflowTemplateEvaluator(newTraceWriter, fileTable, features: null);
+
+                // Create expression token for fromJSON('')
+                var legacyToken = new BasicExpressionToken(null, null, null, "fromJson('')");
+                var newToken = new GitHub.Actions.WorkflowParser.ObjectTemplating.Tokens.BasicExpressionToken(null, null, null, "fromJson('')");
+
+                var contextData = new DictionaryContextData();
+                var newContextData = new GitHub.Actions.Expressions.Data.DictionaryExpressionData();
+                var expressionFunctions = new List<LegacyExpressions.IFunctionInfo>();
+                var newExpressionFunctions = new List<GitHub.Actions.Expressions.IFunctionInfo>();
+
+                // Act - Both should throw
+                Exception legacyException = null;
+                Exception newException = null;
+
+                try
+                {
+                    legacyEvaluator.EvaluateStepDisplayName(legacyToken, contextData, expressionFunctions);
+                }
+                catch (Exception ex)
+                {
+                    legacyException = ex;
+                }
+
+                try
+                {
+                    newEvaluator.EvaluateStepName(newToken, newContextData, newExpressionFunctions);
+                }
+                catch (Exception ex)
+                {
+                    newException = ex;
+                }
+
+                // Assert - Both threw exceptions
+                Assert.NotNull(legacyException);
+                Assert.NotNull(newException);
+
+                // Verify the error messages are different (which is why we need semantic comparison)
+                Assert.NotEqual(legacyException.Message, newException.Message);
+
+                // Verify both are JSON parse errors (contain JSON-related error indicators)
+                var legacyFullMsg = GetFullExceptionMessage(legacyException);
+                var newFullMsg = GetFullExceptionMessage(newException);
+
+                // At least one should contain indicators of JSON parsing failure
+                var legacyIsJsonError = legacyFullMsg.Contains("JToken") ||
+                                        legacyFullMsg.Contains("JsonReader") ||
+                                        legacyFullMsg.Contains("fromJson");
+                var newIsJsonError = newFullMsg.Contains("JToken") ||
+                                     newFullMsg.Contains("JsonReader") ||
+                                     newFullMsg.Contains("fromJson");
+
+                Assert.True(legacyIsJsonError, $"Legacy exception should be JSON error: {legacyFullMsg}");
+                Assert.True(newIsJsonError, $"New exception should be JSON error: {newFullMsg}");
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateDefaultInput_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var legacyManager = new ActionManifestManagerLegacy();
+                legacyManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManagerLegacy>(legacyManager);
+
+                var newManager = new ActionManifestManager();
+                newManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManager>(newManager);
+
+                var wrapper = new ActionManifestManagerWrapper();
+                wrapper.Initialize(_hc);
+
+                _ec.Object.ExpressionValues["github"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["strategy"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["matrix"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["steps"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["job"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["runner"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionValues["env"] = new LegacyContextData.DictionaryContextData();
+                _ec.Object.ExpressionFunctions.Add(new LegacyExpressions.FunctionInfo<GitHub.Runner.Worker.Expressions.HashFilesFunction>("hashFiles", 1, 255));
+
+                var result = wrapper.EvaluateDefaultInput(_ec.Object, "testInput", new StringToken(null, null, null, "defaultValue"));
+
+                Assert.Equal("defaultValue", result);
+                Assert.False(_ec.Object.Global.HasActionManifestMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateContainerArguments_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var legacyManager = new ActionManifestManagerLegacy();
+                legacyManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManagerLegacy>(legacyManager);
+
+                var newManager = new ActionManifestManager();
+                newManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManager>(newManager);
+
+                var wrapper = new ActionManifestManagerWrapper();
+                wrapper.Initialize(_hc);
+
+                var arguments = new SequenceToken(null, null, null);
+                arguments.Add(new StringToken(null, null, null, "arg1"));
+                arguments.Add(new StringToken(null, null, null, "arg2"));
+
+                var evaluateContext = new Dictionary<string, LegacyContextData.PipelineContextData>(StringComparer.OrdinalIgnoreCase);
+
+                var result = wrapper.EvaluateContainerArguments(_ec.Object, arguments, evaluateContext);
+
+                Assert.Equal(2, result.Count);
+                Assert.Equal("arg1", result[0]);
+                Assert.Equal("arg2", result[1]);
+                Assert.False(_ec.Object.Global.HasActionManifestMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateContainerEnvironment_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var legacyManager = new ActionManifestManagerLegacy();
+                legacyManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManagerLegacy>(legacyManager);
+
+                var newManager = new ActionManifestManager();
+                newManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManager>(newManager);
+
+                var wrapper = new ActionManifestManagerWrapper();
+                wrapper.Initialize(_hc);
+
+                var environment = new MappingToken(null, null, null);
+                environment.Add(new StringToken(null, null, null, "hello"), new StringToken(null, null, null, "world"));
+
+                var evaluateContext = new Dictionary<string, LegacyContextData.PipelineContextData>(StringComparer.OrdinalIgnoreCase);
+
+                var result = wrapper.EvaluateContainerEnvironment(_ec.Object, environment, evaluateContext);
+
+                Assert.Equal(1, result.Count);
+                Assert.Equal("world", result["hello"]);
+                Assert.False(_ec.Object.Global.HasActionManifestMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateCompositeOutputs_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var legacyManager = new ActionManifestManagerLegacy();
+                legacyManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManagerLegacy>(legacyManager);
+
+                var newManager = new ActionManifestManager();
+                newManager.Initialize(_hc);
+                _hc.SetSingleton<IActionManifestManager>(newManager);
+
+                var wrapper = new ActionManifestManagerWrapper();
+                wrapper.Initialize(_hc);
+
+                var outputDef = new MappingToken(null, null, null);
+                outputDef.Add(new StringToken(null, null, null, "description"), new StringToken(null, null, null, "test output"));
+                outputDef.Add(new StringToken(null, null, null, "value"), new StringToken(null, null, null, "value1"));
+
+                var token = new MappingToken(null, null, null);
+                token.Add(new StringToken(null, null, null, "output1"), outputDef);
+
+                var evaluateContext = new Dictionary<string, LegacyContextData.PipelineContextData>(StringComparer.OrdinalIgnoreCase);
+
+                var result = wrapper.EvaluateCompositeOutputs(_ec.Object, token, evaluateContext);
+
+                Assert.NotNull(result);
+                Assert.False(_ec.Object.Global.HasActionManifestMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        private string GetFullExceptionMessage(Exception ex)
+        {
+            var messages = new List<string>();
+            var current = ex;
+            while (current != null)
+            {
+                messages.Add(current.Message);
+                current = current.InnerException;
+            }
+            return string.Join(" -> ", messages);
+        }
+
+        private void Setup([CallerMemberName] string name = "")
+        {
+            _ecTokenSource?.Dispose();
+            _ecTokenSource = new CancellationTokenSource();
+
+            _hc = new TestHostContext(this, name);
+
+            var expressionValues = new LegacyContextData.DictionaryContextData();
+            var expressionFunctions = new List<LegacyExpressions.IFunctionInfo>();
+
+            _ec = new Mock<IExecutionContext>();
+            _ec.Setup(x => x.Global)
+                .Returns(new GlobalContext
+                {
+                    FileTable = new List<String>(),
+                    Variables = new Variables(_hc, new Dictionary<string, VariableValue>()),
+                    WriteDebug = true,
+                });
+            _ec.Setup(x => x.CancellationToken).Returns(_ecTokenSource.Token);
+            _ec.Setup(x => x.ExpressionValues).Returns(expressionValues);
+            _ec.Setup(x => x.ExpressionFunctions).Returns(expressionFunctions);
+            _ec.Setup(x => x.Write(It.IsAny<string>(), It.IsAny<string>())).Callback((string tag, string message) => { _hc.GetTrace().Info($"{tag}{message}"); });
+            _ec.Setup(x => x.AddIssue(It.IsAny<Issue>(), It.IsAny<ExecutionContextLogOptions>())).Callback((Issue issue, ExecutionContextLogOptions logOptions) => { _hc.GetTrace().Info($"[{issue.Type}]{logOptions.LogMessageOverride ?? issue.Message}"); });
+        }
+
+        private void Teardown()
+        {
+            _hc?.Dispose();
+        }
+    }
+}

src/Test/L0/Worker/PipelineTemplateEvaluatorWrapperL0.cs

@@ -0,0 +1,550 @@
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.DistributedTask.Pipelines.ContextData;
+using GitHub.DistributedTask.Pipelines.ObjectTemplating;
+using GitHub.DistributedTask.WebApi;
+using GitHub.Runner.Common;
+using GitHub.Runner.Sdk;
+using GitHub.Runner.Worker;
+using LegacyContextData = GitHub.DistributedTask.Pipelines.ContextData;
+using LegacyExpressions = GitHub.DistributedTask.Expressions2;
+using Moq;
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Xunit;
+
+namespace GitHub.Runner.Common.Tests.Worker
+{
+    public sealed class PipelineTemplateEvaluatorWrapperL0
+    {
+        private CancellationTokenSource _ecTokenSource;
+        private Mock<IExecutionContext> _ec;
+        private TestHostContext _hc;
+
+        // -------------------------------------------------------------------
+        // EvaluateAndCompare core behavior
+        // -------------------------------------------------------------------
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_DoesNotRecordMismatch_WhenResultsMatch()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                var token = new StringToken(null, null, null, "test-value");
+                var contextData = new DictionaryContextData();
+                var expressionFunctions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateStepDisplayName(token, contextData, expressionFunctions);
+
+                Assert.Equal("test-value", result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_SkipsMismatchRecording_WhenCancellationOccursDuringEvaluation()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                // Call EvaluateAndCompare directly: the new evaluator cancels the token
+                // and returns a different value, forcing hasMismatch = true.
+                // Because cancellation flipped during the evaluation window, the
+                // mismatch should be skipped.
+                var result = wrapper.EvaluateAndCompare<string, string>(
+                    "TestCancellationSkip",
+                    () => "legacy-value",
+                    () =>
+                    {
+                        _ecTokenSource.Cancel();
+                        return "different-value";
+                    },
+                    (legacy, @new) => string.Equals(legacy, @new, StringComparison.Ordinal));
+
+                Assert.Equal("legacy-value", result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_RecordsMismatch_WhenResultsDifferWithoutCancellation()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                // Different results without cancellation — mismatch SHOULD be recorded.
+                var result = wrapper.EvaluateAndCompare<string, string>(
+                    "TestMismatchRecorded",
+                    () => "legacy-value",
+                    () => "different-value",
+                    (legacy, @new) => string.Equals(legacy, @new, StringComparison.Ordinal));
+
+                Assert.Equal("legacy-value", result);
+                Assert.True(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        // -------------------------------------------------------------------
+        // Smoke tests — both parsers agree, no mismatch recorded
+        // -------------------------------------------------------------------
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateStepContinueOnError_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new BooleanToken(null, null, null, true);
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateStepContinueOnError(token, contextData, functions);
+
+                Assert.True(result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateStepEnvironment_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new MappingToken(null, null, null);
+                token.Add(new StringToken(null, null, null, "FOO"), new StringToken(null, null, null, "bar"));
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateStepEnvironment(token, contextData, functions, StringComparer.OrdinalIgnoreCase);
+
+                Assert.NotNull(result);
+                Assert.Equal("bar", result["FOO"]);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateStepIf_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new BasicExpressionToken(null, null, null, "true");
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+                var expressionState = new List<KeyValuePair<string, object>>();
+
+                var result = wrapper.EvaluateStepIf(token, contextData, functions, expressionState);
+
+                Assert.True(result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateStepInputs_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new MappingToken(null, null, null);
+                token.Add(new StringToken(null, null, null, "input1"), new StringToken(null, null, null, "val1"));
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateStepInputs(token, contextData, functions);
+
+                Assert.NotNull(result);
+                Assert.Equal("val1", result["input1"]);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateStepTimeout_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new NumberToken(null, null, null, 10);
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateStepTimeout(token, contextData, functions);
+
+                Assert.Equal(10, result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobContainer_EmptyImage_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new StringToken(null, null, null, "");
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateJobContainer(token, contextData, functions);
+
+                Assert.Null(result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobOutput_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new MappingToken(null, null, null);
+                token.Add(new StringToken(null, null, null, "out1"), new StringToken(null, null, null, "val1"));
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateJobOutput(token, contextData, functions);
+
+                Assert.NotNull(result);
+                Assert.Equal("val1", result["out1"]);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateEnvironmentUrl_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new StringToken(null, null, null, "https://example.com");
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateEnvironmentUrl(token, contextData, functions);
+
+                Assert.NotNull(result);
+                var stringResult = result as StringToken;
+                Assert.NotNull(stringResult);
+                Assert.Equal("https://example.com", stringResult.Value);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobDefaultsRun_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var token = new MappingToken(null, null, null);
+                token.Add(new StringToken(null, null, null, "shell"), new StringToken(null, null, null, "bash"));
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateJobDefaultsRun(token, contextData, functions);
+
+                Assert.NotNull(result);
+                Assert.Equal("bash", result["shell"]);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobServiceContainers_Null_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateJobServiceContainers(null, contextData, functions);
+
+                Assert.Null(result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateJobSnapshotRequest_Null_BothParsersAgree()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+                var contextData = new DictionaryContextData();
+                var functions = new List<LegacyExpressions.IFunctionInfo>();
+
+                var result = wrapper.EvaluateJobSnapshotRequest(null, contextData, functions);
+
+                Assert.Null(result);
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        // -------------------------------------------------------------------
+        // JSON parse error equivalence via EvaluateAndCompare
+        // -------------------------------------------------------------------
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_JsonReaderExceptions_TreatedAsEquivalent()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                // Both throw JsonReaderException with different messages — should be treated as equivalent
+                var legacyEx = new Newtonsoft.Json.JsonReaderException("Error reading JToken from JsonReader. Path '', line 0, position 0.");
+                var newEx = new Newtonsoft.Json.JsonReaderException("Error parsing fromJson", new Newtonsoft.Json.JsonReaderException("Unexpected end"));
+
+                Assert.Throws<Newtonsoft.Json.JsonReaderException>(() =>
+                    wrapper.EvaluateAndCompare<string, string>(
+                        "TestJsonEquivalence",
+                        () => throw legacyEx,
+                        () => throw newEx,
+                        (a, b) => string.Equals(a, b, StringComparison.Ordinal)));
+
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_MixedJsonExceptionTypes_TreatedAsEquivalent()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                // Legacy throws Newtonsoft JsonReaderException, new throws System.Text.Json.JsonException
+                var legacyEx = new Newtonsoft.Json.JsonReaderException("Error reading JToken");
+                var newEx = new System.Text.Json.JsonException("Error parsing fromJson");
+
+                Assert.Throws<Newtonsoft.Json.JsonReaderException>(() =>
+                    wrapper.EvaluateAndCompare<string, string>(
+                        "TestMixedJsonTypes",
+                        () => throw legacyEx,
+                        () => throw newEx,
+                        (a, b) => string.Equals(a, b, StringComparison.Ordinal)));
+
+                Assert.False(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void EvaluateAndCompare_NonJsonExceptions_RecordsMismatch()
+        {
+            try
+            {
+                Setup();
+                _ec.Object.Global.Variables.Set(Constants.Runner.Features.CompareWorkflowParser, "true");
+
+                var wrapper = new PipelineTemplateEvaluatorWrapper(_hc, _ec.Object);
+
+                // Both throw non-JSON exceptions with different messages — should record mismatch
+                var legacyEx = new InvalidOperationException("some error");
+                var newEx = new InvalidOperationException("different error");
+
+                Assert.Throws<InvalidOperationException>(() =>
+                    wrapper.EvaluateAndCompare<string, string>(
+                        "TestNonJsonMismatch",
+                        () => throw legacyEx,
+                        () => throw newEx,
+                        (a, b) => string.Equals(a, b, StringComparison.Ordinal)));
+
+                Assert.True(_ec.Object.Global.HasTemplateEvaluatorMismatch);
+            }
+            finally
+            {
+                Teardown();
+            }
+        }
+
+        // -------------------------------------------------------------------
+        // Helpers
+        // -------------------------------------------------------------------
+
+        private void Setup([CallerMemberName] string name = "")
+        {
+            _ecTokenSource?.Dispose();
+            _ecTokenSource = new CancellationTokenSource();
+
+            _hc = new TestHostContext(this, name);
+
+            var expressionValues = new LegacyContextData.DictionaryContextData();
+            var expressionFunctions = new List<LegacyExpressions.IFunctionInfo>();
+
+            _ec = new Mock<IExecutionContext>();
+            _ec.Setup(x => x.Global)
+                .Returns(new GlobalContext
+                {
+                    FileTable = new List<String>(),
+                    Variables = new Variables(_hc, new Dictionary<string, VariableValue>()),
+                    WriteDebug = true,
+                });
+            _ec.Setup(x => x.CancellationToken).Returns(_ecTokenSource.Token);
+            _ec.Setup(x => x.ExpressionValues).Returns(expressionValues);
+            _ec.Setup(x => x.ExpressionFunctions).Returns(expressionFunctions);
+            _ec.Setup(x => x.Write(It.IsAny<string>(), It.IsAny<string>())).Callback((string tag, string message) => { _hc.GetTrace().Info($"{tag}{message}"); });
+            _ec.Setup(x => x.AddIssue(It.IsAny<Issue>(), It.IsAny<ExecutionContextLogOptions>())).Callback((Issue issue, ExecutionContextLogOptions logOptions) => { _hc.GetTrace().Info($"[{issue.Type}]{logOptions.LogMessageOverride ?? issue.Message}"); });
+        }
+
+        private void Teardown()
+        {
+            _hc?.Dispose();
+        }
+    }
+}