Perf: materialize streamed orchestration history incrementally

[berndverst]

Summary

Replaces lazy Concat/Select accumulation in streamed orchestration-history reconstruction with direct List<HistoryEvent> materialization.

The former code built a deeply nested iterator chain. Enumerating that chain dispatches each event through the preceding Concat nodes, so many small chunks produce quadratic iterator work. The new code converts and appends each event exactly once as chunks arrive.

Change

• Streaming history is appended directly to one List<HistoryEvent>.
• The list intentionally relies on geometric growth instead of setting an exact per-chunk capacity, which would itself reallocate and copy for every small chunk.
• Non-streamed past events use a count-sized list.
• New events are added with a direct loop instead of a lazy projection.
• Event conversion, ordering, past/new classification, cancellation, and stream disposal are unchanged.

Tests

Added three focused regressions:

• BuildRuntimeStateAsync_MultiChunkHistoryStream_MaterializesEventsInOrderAndClassifiesNewVsPast
• BuildRuntimeStateAsync_HistoryStreamCanceledMidStream_PropagatesCancellation
• BuildRuntimeStateAsync_ManySingleEventChunks_DoesNotExhibitQuadraticListGrowth

The focused tests and full Worker.Grpc.Tests suite pass.

No public API, wire-format, or replay-behavior changes.

Fixes #772

[Copilot]

Pull request overview

This PR improves worker-side orchestration replay performance by replacing lazy IEnumerable accumulation (Concat/Select) in BuildRuntimeStateAsync with eager, incremental materialization into a single List<HistoryEvent>, preventing quadratic behavior when history is streamed in many chunks.

Changes:

• Materialize streamed and non-streamed PastEvents into a single List<HistoryEvent> as events arrive.
• Add NewEvents to OrchestrationRuntimeState via direct iteration and conversion (no lazy projections).
• Add regression tests covering multi-chunk streaming order/classification and cancellation propagation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Worker/Grpc/GrpcDurableTaskWorker.Processor.cs	Reworks history accumulation to eagerly append converted events instead of chaining lazy Concat/Select.
test/Worker/Grpc.Tests/GrpcDurableTaskWorkerTests.cs	Adds targeted tests for multi-chunk history materialization correctness and cancellation behavior.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/Worker/Grpc/GrpcDurableTaskWorker.Processor.cs:287

• In the streaming path, pastEvents starts at the default capacity and grows via repeated Add calls. For large streamed chunks, this can still trigger multiple intermediate reallocations/copies within a single chunk. Since chunk.Events.Count is available, consider calling List<T>.EnsureCapacity(pastEvents.Count + chunk.Events.Count) per chunk to reduce reallocations while still preserving the intended geometric growth behavior (and it would also align with the PR description’s mention of a per-chunk capacity hint).

                pastEvents = new List<HistoryEvent>();
                await foreach (P.HistoryChunk chunk in streamResponse.ResponseStream.ReadAllAsync(cancellation))
                {
                    foreach (P.HistoryEvent protoEvent in chunk.Events)
                    {

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.