fix: resolve sub-workflow agent discovery

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/src/Aryx.AgentHost/Services/WorkflowDefinitionExtensions.cs

@@ -13,6 +13,32 @@ internal static class WorkflowDefinitionExtensions
             .ToList();
     }
 
+    public static IReadOnlyList<WorkflowNodeDto> GetAllAgentNodes(
+        this WorkflowDefinitionDto workflow,
+        IReadOnlyList<WorkflowDefinitionDto>? workflowLibrary = null)
+    {
+        ArgumentNullException.ThrowIfNull(workflow);
+
+        Dictionary<string, WorkflowDefinitionDto> workflowLibraryMap = CreateWorkflowLibraryMap(workflowLibrary);
+        return GetAllAgentNodes(workflow, workflowLibraryMap);
+    }
+
+    public static IReadOnlyList<WorkflowNodeDto> GetAllAgentNodes(
+        this WorkflowDefinitionDto workflow,
+        IReadOnlyDictionary<string, WorkflowDefinitionDto>? workflowLibrary)
+    {
+        ArgumentNullException.ThrowIfNull(workflow);
+
+        List<WorkflowNodeDto> agentNodes = [];
+        CollectAgentNodes(
+            workflow,
+            workflowLibrary ?? EmptyWorkflowLibrary,
+            agentNodes,
+            new HashSet<string>(StringComparer.Ordinal),
+            new HashSet<WorkflowDefinitionDto>(ReferenceEqualityComparer.Instance));
+        return agentNodes;
+    }
+
     public static bool IsAgentNode(this WorkflowNodeDto node)
     {
         ArgumentNullException.ThrowIfNull(node);
@@ -31,6 +57,28 @@ internal static class WorkflowDefinitionExtensions
         return FirstNonBlank(node.Config.Name, node.Label, node.Id) ?? "agent";
     }
 
+    public static WorkflowDefinitionDto ResolveSubWorkflowDefinition(
+        this WorkflowNodeDto node,
+        IReadOnlyDictionary<string, WorkflowDefinitionDto>? workflowLibrary)
+    {
+        ArgumentNullException.ThrowIfNull(node);
+
+        if (node.Config.InlineWorkflow is not null)
+        {
+            return node.Config.InlineWorkflow;
+        }
+
+        if (!string.IsNullOrWhiteSpace(node.Config.WorkflowId)
+            && workflowLibrary is not null
+            && workflowLibrary.TryGetValue(node.Config.WorkflowId, out WorkflowDefinitionDto? workflow))
+        {
+            return workflow;
+        }
+
+        throw new InvalidOperationException(
+            $"Sub-workflow node \"{node.Id}\" references unknown workflow \"{node.Config.WorkflowId}\".");
+    }
+
     public static bool IsOrchestrationMode(this WorkflowDefinitionDto workflow, string mode)
     {
         ArgumentNullException.ThrowIfNull(workflow);
@@ -39,6 +87,60 @@ internal static class WorkflowDefinitionExtensions
         return string.Equals(workflow.Settings.OrchestrationMode, mode, StringComparison.OrdinalIgnoreCase);
     }
 
+    private static readonly IReadOnlyDictionary<string, WorkflowDefinitionDto> EmptyWorkflowLibrary =
+        new Dictionary<string, WorkflowDefinitionDto>(StringComparer.Ordinal);
+
+    private static void CollectAgentNodes(
+        WorkflowDefinitionDto workflowDefinition,
+        IReadOnlyDictionary<string, WorkflowDefinitionDto> workflowLibrary,
+        List<WorkflowNodeDto> agentNodes,
+        ISet<string> visitedWorkflowIds,
+        ISet<WorkflowDefinitionDto> visitedAnonymousWorkflows)
+    {
+        string? workflowId = NormalizeOptionalString(workflowDefinition.Id);
+        if (workflowId is not null)
+        {
+            if (!visitedWorkflowIds.Add(workflowId))
+            {
+                return;
+            }
+        }
+        else if (!visitedAnonymousWorkflows.Add(workflowDefinition))
+        {
+            return;
+        }
+
+        foreach (WorkflowNodeDto node in workflowDefinition.Graph.Nodes)
+        {
+            if (node.IsAgentNode())
+            {
+                agentNodes.Add(node);
+                continue;
+            }
+
+            if (!string.Equals(node.Kind, "sub-workflow", StringComparison.OrdinalIgnoreCase))
+            {
+                continue;
+            }
+
+            WorkflowDefinitionDto subWorkflow = node.ResolveSubWorkflowDefinition(workflowLibrary);
+            CollectAgentNodes(subWorkflow, workflowLibrary, agentNodes, visitedWorkflowIds, visitedAnonymousWorkflows);
+        }
+    }
+
+    private static Dictionary<string, WorkflowDefinitionDto> CreateWorkflowLibraryMap(
+        IReadOnlyList<WorkflowDefinitionDto>? workflowLibrary)
+    {
+        return workflowLibrary?
+            .Where(candidate => !string.IsNullOrWhiteSpace(candidate.Id))
+            .GroupBy(candidate => candidate.Id, StringComparer.Ordinal)
+            .ToDictionary(group => group.Key, group => group.Last(), StringComparer.Ordinal)
+            ?? new Dictionary<string, WorkflowDefinitionDto>(StringComparer.Ordinal);
+    }
+
+    private static string? NormalizeOptionalString(string? value)
+        => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+
     private static string? FirstNonBlank(params string?[] values)
     {
         foreach (string? value in values)