Fix case-sensitive action dedup allowing duplicate downloads

The deduplication logic introduced in actions#4296 used StringComparer.Ordinal,
so action references differing only by owner/repo casing (e.g.
actions/checkout vs actIONS/checkout) were treated as distinct and
downloaded multiple times. Switch to OrdinalIgnoreCase for all dedup
collections and the GroupBy in GetDownloadInfoAsync.

Fixes actions#3731

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

Author: stefanpenner

src/Runner.Worker/ActionManager.cs

@@ -84,7 +84,7 @@ public sealed class ActionManager : RunnerService, IActionManager
             // Stack-local cache: same action (owner/repo@ref) is resolved only once,
             // even if it appears at multiple depths in a composite tree.
             var resolvedDownloadInfos = batchActionResolution
-                ? new Dictionary<string, WebApi.ActionDownloadInfo>(StringComparer.Ordinal)
+                ? new Dictionary<string, WebApi.ActionDownloadInfo>(StringComparer.OrdinalIgnoreCase)
                 : null;
             var depth = 0;
             // We are running at the start of a job
@@ -858,7 +858,7 @@ private async Task BuildActionContainerAsync(IExecutionContext executionContext,
 
             // Convert to action reference
             var actionReferences = actions
-                .GroupBy(x => GetDownloadInfoLookupKey(x))
+                .GroupBy(x => GetDownloadInfoLookupKey(x), StringComparer.OrdinalIgnoreCase)
                 .Where(x => !string.IsNullOrEmpty(x.Key))
                 .Select(x =>
                 {
@@ -953,7 +953,7 @@ private async Task BuildActionContainerAsync(IExecutionContext executionContext,
                 }
             }
 
-            return actionDownloadInfos.Actions;
+            return new Dictionary<string, WebApi.ActionDownloadInfo>(actionDownloadInfos.Actions, StringComparer.OrdinalIgnoreCase);
         }
 
         /// <summary>
@@ -963,7 +963,7 @@ private async Task BuildActionContainerAsync(IExecutionContext executionContext,
         private async Task ResolveNewActionsAsync(IExecutionContext executionContext, List<Pipelines.ActionStep> actions, Dictionary<string, WebApi.ActionDownloadInfo> resolvedDownloadInfos)
         {
             var actionsToResolve = new List<Pipelines.ActionStep>();
-            var pendingKeys = new HashSet<string>(StringComparer.Ordinal);
+            var pendingKeys = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
             foreach (var action in actions)
             {
                 var lookupKey = GetDownloadInfoLookupKey(action);

src/Test/L0/Worker/ActionManagerL0.cs

@@ -1449,6 +1449,98 @@ public async void PrepareActions_DeduplicatesResolutionAcrossDepthLevels()
             }
         }
 
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public async void PrepareActions_DeduplicatesCaseInsensitiveActionReferences()
+        {
+            // Verifies that action references differing only by owner/repo casing
+            // are deduplicated and resolved only once.
+            // Regression test for https://github.com/actions/runner/issues/3731
+            Environment.SetEnvironmentVariable("ACTIONS_BATCH_ACTION_RESOLUTION", "true");
+            try
+            {
+                //Arrange
+                Setup();
+                // Each action step with pre+post needs 2 IActionRunner instances (pre + post)
+                for (int i = 0; i < 6; i++)
+                {
+                    _hc.EnqueueInstance<IActionRunner>(new Mock<IActionRunner>().Object);
+                }
+
+                var allResolvedKeys = new List<string>();
+                _jobServer.Setup(x => x.ResolveActionDownloadInfoAsync(It.IsAny<Guid>(), It.IsAny<string>(), It.IsAny<Guid>(), It.IsAny<Guid>(), It.IsAny<ActionReferenceList>(), It.IsAny<CancellationToken>()))
+                    .Returns((Guid scopeIdentifier, string hubName, Guid planId, Guid jobId, ActionReferenceList actions, CancellationToken cancellationToken) =>
+                    {
+                        var result = new ActionDownloadInfoCollection { Actions = new Dictionary<string, ActionDownloadInfo>() };
+                        foreach (var action in actions.Actions)
+                        {
+                            var key = $"{action.NameWithOwner}@{action.Ref}";
+                            allResolvedKeys.Add(key);
+                            result.Actions[key] = new ActionDownloadInfo
+                            {
+                                NameWithOwner = action.NameWithOwner,
+                                Ref = action.Ref,
+                                ResolvedNameWithOwner = action.NameWithOwner,
+                                ResolvedSha = $"{action.Ref}-sha",
+                                TarballUrl = $"https://api.github.com/repos/{action.NameWithOwner}/tarball/{action.Ref}",
+                                ZipballUrl = $"https://api.github.com/repos/{action.NameWithOwner}/zipball/{action.Ref}",
+                            };
+                        }
+                        return Task.FromResult(result);
+                    });
+
+                var actions = new List<Pipelines.ActionStep>
+                {
+                    new Pipelines.ActionStep()
+                    {
+                        Name = "action1",
+                        Id = Guid.NewGuid(),
+                        Reference = new Pipelines.RepositoryPathReference()
+                        {
+                            Name = "TingluoHuang/runner_L0",
+                            Ref = "RepositoryActionWithWrapperActionfile_Node",
+                            RepositoryType = "GitHub"
+                        }
+                    },
+                    new Pipelines.ActionStep()
+                    {
+                        Name = "action2",
+                        Id = Guid.NewGuid(),
+                        Reference = new Pipelines.RepositoryPathReference()
+                        {
+                            Name = "tingluohuang/RUNNER_L0",
+                            Ref = "RepositoryActionWithWrapperActionfile_Node",
+                            RepositoryType = "GitHub"
+                        }
+                    },
+                    new Pipelines.ActionStep()
+                    {
+                        Name = "action3",
+                        Id = Guid.NewGuid(),
+                        Reference = new Pipelines.RepositoryPathReference()
+                        {
+                            Name = "TINGLUOHUANG/Runner_L0",
+                            Ref = "RepositoryActionWithWrapperActionfile_Node",
+                            RepositoryType = "GitHub"
+                        }
+                    }
+                };
+
+                //Act
+                await _actionManager.PrepareActionsAsync(_ec.Object, actions);
+
+                //Assert
+                // All three references should deduplicate to a single resolve call
+                Assert.Equal(1, allResolvedKeys.Count);
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable("ACTIONS_BATCH_ACTION_RESOLUTION", null);
+                Teardown();
+            }
+        }
+
         [Fact]
         [Trait("Level", "L0")]
         [Trait("Category", "Worker")]