Partial orchestration workitem completion support (Merge after next dts dp release)

src/Grpc/orchestrator_service.proto

@@ -356,6 +356,13 @@ message OrchestratorResponse {
 
     // Whether or not a history is required to complete the original OrchestratorRequest and none was provided.
     bool requiresHistory = 7;
+
+    // True if this is a partial (chunked) completion. The backend must keep the work item open until the final chunk (isPartial=false).
+    bool isPartial = 8;
+
+    // Zero-based position of the current chunk within a chunked completion sequence.
+    // This field is omitted for non-chunked completions.
+    google.protobuf.Int32Value chunkIndex = 9;
 }
 
 message CreateInstanceRequest {

src/Grpc/versions.txt

@@ -1,2 +1,2 @@
-# The following files were downloaded from branch main at 2025-11-14 16:36:47 UTC
-https://raw.githubusercontent.com/microsoft/durabletask-protobuf/9f762f1301b91e3e7c736b9c5a29c2e09f2a850e/protos/orchestrator_service.proto
+# The following files were downloaded from branch main at 2025-12-05 19:49:32 UTC
+https://raw.githubusercontent.com/microsoft/durabletask-protobuf/1774123378045dd87cd3307c50da4cdd4551a817/protos/orchestrator_service.proto

src/InProcessTestHost/Sidecar/Grpc/TaskHubGrpcServer.cs

@@ -5,6 +5,7 @@
 using System.Diagnostics;
 using System.Globalization;
 using DurableTask.Core;
+using DurableTask.Core.Command;
 using DurableTask.Core.History;
 using DurableTask.Core.Query;
 using Google.Protobuf.WellKnownTypes;
@@ -30,6 +31,29 @@ public class TaskHubGrpcServer : P.TaskHubSidecarService.TaskHubSidecarServiceBa
 
     readonly ConcurrentDictionary<string, TaskCompletionSource<GrpcOrchestratorExecutionResult>> pendingOrchestratorTasks = new(StringComparer.OrdinalIgnoreCase);
     readonly ConcurrentDictionary<string, TaskCompletionSource<ActivityExecutionResult>> pendingActivityTasks = new(StringComparer.OrdinalIgnoreCase);
+    readonly ConcurrentDictionary<string, PartialOrchestratorChunk> partialOrchestratorChunks = new(StringComparer.OrdinalIgnoreCase);
+
+    /// <summary>
+    /// Helper class to accumulate partial orchestrator chunks.
+    /// </summary>
+    sealed class PartialOrchestratorChunk
+    {
+        readonly object lockObject = new();
+
+        public TaskCompletionSource<GrpcOrchestratorExecutionResult> TaskCompletionSource { get; set; } = null!;
+        public List<OrchestratorAction> AccumulatedActions { get; } = new();
+
+        /// <summary>
+        /// Thread-safely adds actions to the accumulated actions list.
+        /// </summary>
+        public void AddActions(IEnumerable<OrchestratorAction> actions)
+        {
+            lock (this.lockObject)
+            {
+                this.AccumulatedActions.AddRange(actions);
+            }
+        }
+    }
 
     readonly ILogger log;
     readonly IOrchestrationService service;
@@ -191,7 +215,7 @@ async Task WaitForWorkItemClientConnection()
     /// <returns>A create instance response.</returns>
     public override async Task<P.CreateInstanceResponse> StartInstance(P.CreateInstanceRequest request, ServerCallContext context)
     {
-        var instance = new OrchestrationInstance
+        OrchestrationInstance instance = new OrchestrationInstance
         {
             InstanceId = request.InstanceId ?? Guid.NewGuid().ToString("N"),
             ExecutionId = Guid.NewGuid().ToString(),
@@ -535,6 +559,51 @@ static P.GetInstanceResponse CreateGetInstanceResponse(OrchestrationState state,
     /// <returns>Returns an empty ack back to the remote SDK that we've received the completion.</returns>
     public override Task<P.CompleteTaskResponse> CompleteOrchestratorTask(P.OrchestratorResponse request, ServerCallContext context)
     {
+        if (request.IsPartial)
+        {
+            // This is a partial chunk - accumulate actions but don't complete yet
+            PartialOrchestratorChunk partialChunk = this.partialOrchestratorChunks.GetOrAdd(
+                request.InstanceId,
+                _ =>
+                {
+                    // First chunk - get the TCS and initialize the partial chunk
+                    if (!this.pendingOrchestratorTasks.TryGetValue(request.InstanceId, out TaskCompletionSource<GrpcOrchestratorExecutionResult>? tcs))
+                    {
+                        throw new RpcException(new Status(StatusCode.NotFound, $"Orchestration with instance ID '{request.InstanceId}' not found"));
+                    }
+
+                    return new PartialOrchestratorChunk
+                    {
+                        TaskCompletionSource = tcs,
+                    };
+                });
+
+            // Accumulate actions from this chunk (thread-safe)
+            partialChunk.AddActions(request.Actions.Select(ProtobufUtils.ToOrchestratorAction));
+
+            return EmptyCompleteTaskResponse;
+        }
+
+        // This is the final chunk (or a single non-chunked response)
+        if (this.partialOrchestratorChunks.TryRemove(request.InstanceId, out PartialOrchestratorChunk? existingPartialChunk))
+        {
+            // We've been accumulating chunks - combine with final chunk (thread-safe)
+            existingPartialChunk.AddActions(request.Actions.Select(ProtobufUtils.ToOrchestratorAction));
+
+            GrpcOrchestratorExecutionResult res = new()
+            {
+                Actions = existingPartialChunk.AccumulatedActions,
+                CustomStatus = request.CustomStatus,
+            };
+
+            // Remove the TCS from pending tasks and complete it
+            this.pendingOrchestratorTasks.TryRemove(request.InstanceId, out _);
+            existingPartialChunk.TaskCompletionSource.TrySetResult(res);
+
+            return EmptyCompleteTaskResponse;
+        }
+
+        // Single non-chunked response (no partial chunks)
         if (!this.pendingOrchestratorTasks.TryRemove(
             request.InstanceId,
             out TaskCompletionSource<GrpcOrchestratorExecutionResult>? tcs))
@@ -691,7 +760,7 @@ async Task<GrpcOrchestratorExecutionResult> ITaskExecutor.ExecuteOrchestrator(
         IEnumerable<HistoryEvent> pastEvents,
         IEnumerable<HistoryEvent> newEvents)
     {
-        var executionStartedEvent = pastEvents.OfType<ExecutionStartedEvent>().FirstOrDefault();
+        ExecutionStartedEvent? executionStartedEvent = pastEvents.OfType<ExecutionStartedEvent>().FirstOrDefault();
 
         P.OrchestrationTraceContext? orchestrationTraceContext = executionStartedEvent?.ParentTraceContext?.SpanId is not null
             ? new P.OrchestrationTraceContext
@@ -708,7 +777,7 @@ async Task<GrpcOrchestratorExecutionResult> ITaskExecutor.ExecuteOrchestrator(
 
         try
         {
-            var orkRequest = new P.OrchestratorRequest
+            P.OrchestratorRequest orkRequest = new P.OrchestratorRequest
             {
                 InstanceId = instance.InstanceId,
                 ExecutionId = instance.ExecutionId,
@@ -836,6 +905,7 @@ TaskCompletionSource<GrpcOrchestratorExecutionResult> CreateTaskCompletionSource
     void RemoveOrchestratorTaskCompletionSource(string instanceId)
     {
         this.pendingOrchestratorTasks.TryRemove(instanceId, out _);
+        this.partialOrchestratorChunks.TryRemove(instanceId, out _);
     }
 
     TaskCompletionSource<ActivityExecutionResult> CreateTaskCompletionSourceForActivity(string instanceId, int taskId)

src/Worker/Grpc/GrpcDurableTaskWorker.Processor.cs

@@ -2,11 +2,13 @@
 // Licensed under the MIT License.
 
 using System.Diagnostics;
+using System.Linq;
 using System.Text;
 using DurableTask.Core;
 using DurableTask.Core.Entities;
 using DurableTask.Core.Entities.OperationFormat;
 using DurableTask.Core.History;
+using Google.Protobuf;
 using Microsoft.DurableTask.Abstractions;
 using Microsoft.DurableTask.Entities;
 using Microsoft.DurableTask.Tracing;
@@ -755,7 +757,10 @@ await this.client.AbandonTaskOrchestratorWorkItemAsync(
                 response.Actions.Count,
                 GetActionsListForLogging(response.Actions));
 
-            await this.client.CompleteOrchestratorTaskAsync(response, cancellationToken: cancellationToken);
+            await this.CompleteOrchestratorTaskWithChunkingAsync(
+                response,
+                this.worker.grpcOptions.CompleteOrchestrationWorkItemChunkSizeInBytes,
+                cancellationToken);
         }
 
         async Task OnRunActivityAsync(P.ActivityRequest request, string completionToken, CancellationToken cancellation)
@@ -914,5 +919,139 @@ async Task OnRunEntityBatchAsync(
 
             await this.client.CompleteEntityTaskAsync(response, cancellationToken: cancellation);
         }
+
+        /// <summary>
+        /// Completes an orchestration task with automatic chunking if the response exceeds the maximum size.
+        /// </summary>
+        /// <param name="response">The orchestrator response to send.</param>
+        /// <param name="maxChunkBytes">The maximum size in bytes for each chunk.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        async Task CompleteOrchestratorTaskWithChunkingAsync(
+            P.OrchestratorResponse response,
+            int maxChunkBytes,
+            CancellationToken cancellationToken)
+        {
+            // Validate that no single action exceeds the maximum chunk size
+            static P.TaskFailureDetails? ValidateActionsSize(IEnumerable<P.OrchestratorAction> actions, int maxChunkBytes)
+            {
+                foreach (P.OrchestratorAction action in actions)
+                {
+                    int actionSize = action.CalculateSize();
+                    if (actionSize > maxChunkBytes)
+                    {
+                        // TODO: large payload doc is not available yet on aka.ms, add doc link to below error message
+                        string errorMessage = $"A single orchestrator action of type {action.OrchestratorActionTypeCase} with id {action.Id} " +
+                            $"exceeds the {maxChunkBytes / 1024.0 / 1024.0:F2}MB limit: {actionSize / 1024.0 / 1024.0:F2}MB. " +
+                            "Enable large-payload externalization to Azure Blob Storage to support oversized actions.";
+                        return new P.TaskFailureDetails
+                        {
+                            ErrorType = typeof(InvalidOperationException).FullName,
+                            ErrorMessage = errorMessage,
+                            IsNonRetriable = true,
+                        };
+                    }
+                }
+
+                return null;
+            }
+
+            P.TaskFailureDetails? validationFailure = ValidateActionsSize(response.Actions, maxChunkBytes);
+            if (validationFailure != null)
+            {
+                // Complete the orchestration with a failed status and failure details
+                P.OrchestratorResponse failureResponse = new()
+                {
+                    InstanceId = response.InstanceId,
+                    CompletionToken = response.CompletionToken,
+                    OrchestrationTraceContext = response.OrchestrationTraceContext,
+                    Actions =
+                    {
+                        new P.OrchestratorAction
+                        {
+                            CompleteOrchestration = new P.CompleteOrchestrationAction
+                            {
+                                OrchestrationStatus = P.OrchestrationStatus.Failed,
+                                FailureDetails = validationFailure,
+                            },
+                        },
+                    },
+                };
+
+                await this.client.CompleteOrchestratorTaskAsync(failureResponse, cancellationToken: cancellationToken);
+                return;
+            }
+
+            // Helper to add an action to the current chunk if it fits
+            static bool TryAddAction(
+                Google.Protobuf.Collections.RepeatedField<P.OrchestratorAction> dest,
+                P.OrchestratorAction action,
+                ref int currentSize,
+                int maxChunkBytes)
+            {
+                int actionSize = action.CalculateSize();
+                if (currentSize + actionSize > maxChunkBytes)
+                {
+                    return false;
+                }
+
+                dest.Add(action);
+                currentSize += actionSize;
+                return true;
+            }
+
+            // Check if the entire response fits in one chunk
+            int totalSize = response.CalculateSize();
+            if (totalSize <= maxChunkBytes)
+            {
+                // Response fits in one chunk, send it directly (isPartial defaults to false)
+                await this.client.CompleteOrchestratorTaskAsync(response, cancellationToken: cancellationToken);
+                return;
+            }
+
+            // Response is too large, split into multiple chunks
+            int actionsCompletedSoFar = 0, chunkIndex = 0;
+            List<P.OrchestratorAction> allActions = response.Actions.ToList();
+            bool isPartial = true;
+
+            while (isPartial)
+            {
+                P.OrchestratorResponse chunkedResponse = new()
+                {
+                    InstanceId = response.InstanceId,
+                    CustomStatus = response.CustomStatus,
+                    CompletionToken = response.CompletionToken,
+                    RequiresHistory = response.RequiresHistory,
+                    NumEventsProcessed = 0,
+                    ChunkIndex = chunkIndex,
+                };
+
+                int chunkPayloadSize = 0;
+
+                // Fill the chunk with actions until we reach the size limit
+                while (actionsCompletedSoFar < allActions.Count &&
+                       TryAddAction(chunkedResponse.Actions, allActions[actionsCompletedSoFar], ref chunkPayloadSize, maxChunkBytes))
+                {
+                    actionsCompletedSoFar++;
+                }
+
+                // Determine if this is a partial chunk (more actions remaining)
+                isPartial = actionsCompletedSoFar < allActions.Count;
+                chunkedResponse.IsPartial = isPartial;
+
+                if (chunkIndex == 0)
+                {
+                    // The first chunk preserves the original response's NumEventsProcessed value (null)
+                    // When this is set to null, backend by default handles all the messages in the workitem.
+                    // For subsequent chunks, we set it to 0 since all messages are already handled in first chunk.
+                    chunkedResponse.NumEventsProcessed = null;
+                    chunkedResponse.OrchestrationTraceContext = response.OrchestrationTraceContext;
+                }
+
+                chunkIndex++;
+
+                // Send the chunk
+                await this.client.CompleteOrchestratorTaskAsync(chunkedResponse, cancellationToken: cancellationToken);
+            }
+        }
     }
 }

src/Worker/Grpc/GrpcDurableTaskWorkerOptions.cs

@@ -10,6 +10,18 @@ namespace Microsoft.DurableTask.Worker.Grpc;
 /// </summary>
 public sealed class GrpcDurableTaskWorkerOptions : DurableTaskWorkerOptions
 {
+    /// <summary>
+    /// The minimum allowed size (in bytes) for complete orchestration work item chunks.
+    /// </summary>
+    public const int MinCompleteOrchestrationWorkItemChunkSizeInBytes = 1 * 1024 * 1024; // 1 MB
+
+    /// <summary>
+    /// The maximum allowed size (in bytes) for complete orchestration work item chunks.
+    /// </summary>
+    public const int MaxCompleteOrchestrationWorkItemChunkSizeInBytes = 4_089_446; // 3.9 MB
+
+    int completeOrchestrationWorkItemChunkSizeInBytes = MaxCompleteOrchestrationWorkItemChunkSizeInBytes;
+
     /// <summary>
     /// Gets or sets the address of the gRPC endpoint to connect to. Default is localhost:4001.
     /// </summary>
@@ -31,6 +43,38 @@ public sealed class GrpcDurableTaskWorkerOptions : DurableTaskWorkerOptions
     /// </summary>
     public HashSet<P.WorkerCapability> Capabilities { get; } = new() { P.WorkerCapability.HistoryStreaming };
 
+    /// <summary>
+    /// Gets or sets the maximum size of all actions in a complete orchestration work item chunk.
+    /// The default value is 3.9MB. We leave some headroom to account for request size overhead.
+    /// </summary>
+    /// <remarks>
+    /// This value is used to limit the size of the complete orchestration work item request.
+    /// If the response exceeds this limit, it will be automatically split into multiple chunks of maximum size CompleteOrchestrationWorkItemChunkSizeInBytes
+    /// </remarks>
+    /// <exception cref="ArgumentOutOfRangeException">
+    /// Thrown when the value is less than 1 MB or greater than 3.9 MB.
+    /// </exception>
+    public int CompleteOrchestrationWorkItemChunkSizeInBytes
+    {
+        get => this.completeOrchestrationWorkItemChunkSizeInBytes;
+        set
+        {
+            if (value < MinCompleteOrchestrationWorkItemChunkSizeInBytes ||
+                value > MaxCompleteOrchestrationWorkItemChunkSizeInBytes)
+            {
+                string message = $"{nameof(CompleteOrchestrationWorkItemChunkSizeInBytes)} must be between " +
+                    $"{MinCompleteOrchestrationWorkItemChunkSizeInBytes} bytes (1 MB) and " +
+                    $"{MaxCompleteOrchestrationWorkItemChunkSizeInBytes} bytes (3.9 MB), inclusive.";
+                throw new ArgumentOutOfRangeException(
+                    nameof(this.CompleteOrchestrationWorkItemChunkSizeInBytes),
+                    value,
+                    message);
+            }
+
+            this.completeOrchestrationWorkItemChunkSizeInBytes = value;
+        }
+    }
+
     /// <summary>
     /// Gets the internal protocol options. These are used to control backend-dependent features.
     /// </summary>