Batch and deduplicate action resolution across composite depths

Thread a cache through PrepareActionsRecursiveAsync so the same action
is resolved at most once regardless of depth. Collect sub-actions from
all sibling composites and resolve them in one API call instead of one
per composite.

~30-composite internal workflow went from ~20 resolve calls to 3-4.

Fixes #3731

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

Author: Stefan Penner

src/Runner.Worker/ActionManager.cs

@@ -66,6 +66,7 @@ public sealed class ActionManager : RunnerService, IActionManager
         private readonly Dictionary<Guid, Stack<Pipelines.ActionStep>> _cachedEmbeddedPostSteps = new();
         public Dictionary<Guid, Stack<Pipelines.ActionStep>> CachedEmbeddedPostSteps => _cachedEmbeddedPostSteps;
 
+
         public async Task<PrepareResult> PrepareActionsAsync(IExecutionContext executionContext, IEnumerable<Pipelines.JobStep> steps, Guid rootStepId = default(Guid))
         {
             // Assert inputs
@@ -79,6 +80,9 @@ public sealed class ActionManager : RunnerService, IActionManager
                 PreStepTracker = new Dictionary<Guid, IActionRunner>()
             };
             var containerSetupSteps = new List<JobExtensionRunner>();
+            // 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 = new Dictionary<string, WebApi.ActionDownloadInfo>(StringComparer.Ordinal);
             var depth = 0;
             // We are running at the start of a job
             if (rootStepId == default(Guid))
@@ -105,7 +109,7 @@ public sealed class ActionManager : RunnerService, IActionManager
             PrepareActionsState result = new PrepareActionsState();
             try
             {
-                result = await PrepareActionsRecursiveAsync(executionContext, state, actions, depth, rootStepId);
+                result = await PrepareActionsRecursiveAsync(executionContext, state, actions, resolvedDownloadInfos, depth, rootStepId);
             }
             catch (FailedToResolveActionDownloadInfoException ex)
             {
@@ -161,13 +165,14 @@ public sealed class ActionManager : RunnerService, IActionManager
             return new PrepareResult(containerSetupSteps, result.PreStepTracker);
         }
 
-        private async Task<PrepareActionsState> PrepareActionsRecursiveAsync(IExecutionContext executionContext, PrepareActionsState state, IEnumerable<Pipelines.ActionStep> actions, Int32 depth = 0, Guid parentStepId = default(Guid))
+        private async Task<PrepareActionsState> PrepareActionsRecursiveAsync(IExecutionContext executionContext, PrepareActionsState state, IEnumerable<Pipelines.ActionStep> actions, Dictionary<string, WebApi.ActionDownloadInfo> resolvedDownloadInfos, Int32 depth = 0, Guid parentStepId = default(Guid))
         {
             ArgUtil.NotNull(executionContext, nameof(executionContext));
             if (depth > Constants.CompositeActionsMaxDepth)
             {
                 throw new Exception($"Composite action depth exceeded max depth {Constants.CompositeActionsMaxDepth}");
             }
+
             var repositoryActions = new List<Pipelines.ActionStep>();
 
             foreach (var action in actions)
@@ -195,27 +200,29 @@ public sealed class ActionManager : RunnerService, IActionManager
 
             if (repositoryActions.Count > 0)
             {
-                // Get the download info
-                var downloadInfos = await GetDownloadInfoAsync(executionContext, repositoryActions);
+                // Resolve download info, skipping any actions already cached.
+                await ResolveNewActionsAsync(executionContext, repositoryActions, resolvedDownloadInfos);
 
-                // Download each action
+                // Download each action.
                 foreach (var action in repositoryActions)
                 {
                     var lookupKey = GetDownloadInfoLookupKey(action);
                     if (string.IsNullOrEmpty(lookupKey))
                     {
                         continue;
                     }
-
-                    if (!downloadInfos.TryGetValue(lookupKey, out var downloadInfo))
+                    if (!resolvedDownloadInfos.TryGetValue(lookupKey, out var downloadInfo))
                     {
                         throw new Exception($"Missing download info for {lookupKey}");
                     }
-
                     await DownloadRepositoryActionAsync(executionContext, downloadInfo);
                 }
 
-                // More preparation based on content in the repository (action.yml)
+                // Parse action.yml and collect composite sub-actions for batched
+                // resolution below. Pre/post step registration is deferred until
+                // after recursion so that HasPre/HasPost reflect the full subtree.
+                var nextLevel = new List<(Pipelines.ActionStep action, Guid parentId)>();
+
                 foreach (var action in repositoryActions)
                 {
                     var setupInfo = PrepareRepositoryActionAsync(executionContext, action);
@@ -247,8 +254,35 @@ public sealed class ActionManager : RunnerService, IActionManager
                     }
                     else if (setupInfo != null && setupInfo.Steps != null && setupInfo.Steps.Count > 0)
                     {
-                        state = await PrepareActionsRecursiveAsync(executionContext, state, setupInfo.Steps, depth + 1, action.Id);
+                        foreach (var step in setupInfo.Steps)
+                        {
+                            nextLevel.Add((step, action.Id));
+                        }
+                    }
+                }
+
+                // Resolve all next-level sub-actions in one batch API call,
+                // then recurse per parent (which hits the cache, not the API).
+                if (nextLevel.Count > 0)
+                {
+                    var nextLevelRepoActions = nextLevel
+                        .Where(x => x.action.Reference.Type == Pipelines.ActionSourceType.Repository)
+                        .Select(x => x.action)
+                        .ToList();
+                    await ResolveNewActionsAsync(executionContext, nextLevelRepoActions, resolvedDownloadInfos);
+
+                    foreach (var group in nextLevel.GroupBy(x => x.parentId))
+                    {
+                        var groupActions = group.Select(x => x.action).ToList();
+                        state = await PrepareActionsRecursiveAsync(executionContext, state, groupActions, resolvedDownloadInfos, depth + 1, group.Key);
                     }
+                }
+
+                // Register pre/post steps after recursion so that HasPre/HasPost
+                // are correct (they depend on _cachedEmbeddedPreSteps/PostSteps
+                // being populated by the recursive calls above).
+                foreach (var action in repositoryActions)
+                {
                     var repoAction = action.Reference as Pipelines.RepositoryPathReference;
                     if (repoAction.RepositoryType != Pipelines.PipelineConstants.SelfAlias)
                     {
@@ -754,6 +788,33 @@ private async Task BuildActionContainerAsync(IExecutionContext executionContext,
             return actionDownloadInfos.Actions;
         }
 
+        /// <summary>
+        /// Only resolves actions not already in resolvedDownloadInfos.
+        /// Results are cached for reuse at deeper recursion levels.
+        /// </summary>
+        private async Task ResolveNewActionsAsync(IExecutionContext executionContext, List<Pipelines.ActionStep> actions, Dictionary<string, WebApi.ActionDownloadInfo> resolvedDownloadInfos)
+        {
+            var actionsToResolve = new List<Pipelines.ActionStep>();
+            foreach (var action in actions)
+            {
+                var lookupKey = GetDownloadInfoLookupKey(action);
+                if (!string.IsNullOrEmpty(lookupKey) && !resolvedDownloadInfos.ContainsKey(lookupKey))
+                {
+                    actionsToResolve.Add(action);
+                }
+            }
+
+            if (actionsToResolve.Count > 0)
+            {
+                var downloadInfos = await GetDownloadInfoAsync(executionContext, actionsToResolve);
+                foreach (var kvp in downloadInfos)
+                {
+                    resolvedDownloadInfos[kvp.Key] = kvp.Value;
+                }
+            }
+        }
+
+
         private async Task DownloadRepositoryActionAsync(IExecutionContext executionContext, WebApi.ActionDownloadInfo downloadInfo)
         {
             Trace.Entering();