Add stateful-history delta work items to the workflow worker

[JoshVanL]

The sidecar re-sends a workflow instance's entire committed history to the worker on every turn. This adds the worker half of the "stateful history" optimization so that, once a worker is warm for an instance on a work-item stream, the sidecar sends only the new committed events (the delta) and the worker reconstructs the full history from its own cache. It mirrors the Go (durabletask-go) and Python SDK implementations and is on by default.

Protocol (src/Dapr.Workflow.Grpc/orchestrator_service.proto, compiled by Grpc.Tools at build time):

• Add the CachedHistory message and WorkflowRequest.cachedHistory.
• Add GetWorkItemsRequest.capabilities and WORKER_CAPABILITY_STATEFUL_HISTORY (reserving the never-implemented WORKER_CAPABILITY_HISTORY_STREAMING).

Worker (src/Dapr.Workflow/Worker/Grpc):

• WorkflowHistoryCache: a per-stream cache of each instance's committed history, bounded by a sliding TTL, an instance-count cap, and a byte budget with LRU eviction. Injectable clock for deterministic tests.
• GrpcProtocolHandler: advertise the capability; before each turn resolve the full committed history (cached prefix + delta on a hit, or a GetInstanceHistory fetch on a miss) and normalize request.PastEvents so the handler stays oblivious to the delta protocol; after each turn cache the committed history, or drop it on a CompleteWorkflow action (completed, failed, terminated, or continued-as-new). Reset the cache on reconnect and reclaim idle entries with a PeriodicTimer janitor.

Correctness never depends on the cache: any miss (cold stream, eviction, desync) self-heals via the existing GetInstanceHistory fallback, so this only changes per-turn bandwidth, not results.

[WhitWaldo]

@JoshVanL This is intended for 1.19, right? I'll defer merging this until we have an RC to run integration tests against.

[Copilot]

Pull request overview

This PR implements the worker side of the “stateful history” optimization for Dapr Workflow’s work-item stream: when a worker is warm for an instance, the sidecar can send only the newly committed history events (delta) and the worker reconstructs the full committed history using a per-stream cache, falling back to GetInstanceHistory on misses.

Changes:

• Extends the gRPC protocol with CachedHistory, WorkflowRequest.cachedHistory, and GetWorkItemsRequest.capabilities plus WORKER_CAPABILITY_STATEFUL_HISTORY.
• Adds a per-stream WorkflowHistoryCache with TTL/LRU eviction and integrates it into GrpcProtocolHandler (advertise capability, resolve deltas, cache after turns, reset on reconnect, periodic sweep).
• Exposes runtime knobs via WorkflowRuntimeOptions and wires them through WorkflowWorker; adds tests for cache bounds and end-to-end delta behavior.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Dapr.Workflow.Test/Worker/Grpc/WorkflowHistoryCacheTests.cs	Adds unit tests for TTL/LRU/count/byte-bound behavior of the history cache.
test/Dapr.Workflow.Test/Worker/Grpc/GrpcProtocolHandlerStatefulHistoryTests.cs	Adds flow tests for capability advertisement and delta reconstruction behavior through the real streaming loop.
src/Dapr.Workflow/Worker/WorkflowWorker.cs	Wires new runtime options into GrpcProtocolHandler construction.
src/Dapr.Workflow/Worker/Grpc/WorkflowHistoryCache.cs	Introduces the per-stream committed-history cache with eviction and byte accounting.
src/Dapr.Workflow/Worker/Grpc/GrpcProtocolHandler.cs	Adds capability advertisement, delta resolution, cache maintenance, and janitor sweep logic.
src/Dapr.Workflow.Grpc/orchestrator_service.proto	Defines the stateful-history protocol surface (CachedHistory, capabilities, enum updates).
src/Dapr.Workflow.Abstractions/WorkflowRuntimeOptions.cs	Adds configuration properties to control stateful-history and cache bounds.

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[JoshVanL]

@WhitWaldo yes exactly, we can keep in draft in the meantime

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Suppressed comments (1)

src/Dapr.Workflow/Worker/Grpc/WorkflowHistoryCache.cs:203

• Evicting one entry at a time while rescanning the entire dictionary makes byte-budget eviction quadratic. A newly cached history that consumes most or all of the budget can evict up to 100,000 existing entries, performing roughly O(n²) comparisons while holding the global cache lock and blocking every workflow turn using the cache. Maintain LRU order incrementally (for example, dictionary plus linked list), or identify all required victims in one ordered pass.

            var victim = LeastRecentlyUsedExcept(keep);
            if (victim is null)
            {
                return;
            }

            RemoveLocked(victim);