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), Python, and .NET SDK implementations and is on by default.

Worker (durabletask-client):

• 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.
• DurableTaskGrpcWorker: advertise WORKER_CAPABILITY_STATEFUL_HISTORY in GetWorkItemsRequest, reset the cache on every reconnect (the sidecar drops the old stream's warm set), and reclaim idle entries with a daemon janitor stopped on close.
• OrchestratorRunner: before replay, resolve the full committed history (cached prefix + delta on a hit, or a GetInstanceHistory fetch on a miss) instead of using the request's pastEvents directly; after replay, cache the committed history, or drop it once the instance ends (a CompleteWorkflow action, covering completed/failed/terminated/continued-as-new). A TerminateWorkflow action targets a different instance and is deliberately not treated as a reset.

Correctness never depends on the cache: any miss (cold stream, eviction, desync) self-heals via the GetInstanceHistory fallback, so this only changes per-turn bandwidth, not results. A fallback fetch that fails abandons the work item for backend redelivery rather than completing with a partial history.

Configuration (DurableTaskGrpcWorkerBuilder):

• disableStatefulHistory to opt out, plus historyCacheTtl, historyCacheMaxInstances, and historyCacheMaxBytes to tune the bounds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.89%. Comparing base (f42e0d2) to head (7a6842a).

Additional details and impacted files

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##             master    #1777   +/-   ##
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  Coverage     76.89%   76.89%           
  Complexity     2307     2307           
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  Files           244      244           
  Lines          7163     7163           
  Branches        753      753           
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  Hits           5508     5508           
  Misses         1288     1288           
  Partials        367      367           

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[Copilot]

Pull request overview

Adds the worker-side implementation of the “stateful history” optimization so the sidecar can send only committed-history deltas on a warm work-item stream, with safe self-healing via GetInstanceHistory on cache misses.

Changes:

• Introduces a per-stream WorkflowHistoryCache (TTL + LRU bounds) and uses it to reconstruct full committed history from deltas.
• Updates DurableTaskGrpcWorker/OrchestratorRunner to advertise the capability, reset cache on reconnect, and abandon (drop stream) when history recovery fails.
• Adds unit + worker-level + end-to-end integration tests validating cache behavior and actual on-the-wire delta delivery.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk-workflows/src/main/java/io/dapr/workflows/runtime/WorkflowRuntimeBuilder.java	Exposes stateful-history configuration knobs on the workflow runtime builder and forwards them to the worker builder.
sdk-workflows/src/test/java/io/dapr/workflows/runtime/WorkflowRuntimeBuilderTest.java	Verifies default enablement and forwarding of stateful-history options (via reflection).
durabletask-client/src/main/java/io/dapr/durabletask/DurableTaskGrpcWorkerBuilder.java	Adds stateful-history configuration fields and builder methods.
durabletask-client/src/main/java/io/dapr/durabletask/DurableTaskGrpcWorker.java	Advertises capability, manages per-stream cache lifecycle, and runs a janitor sweep for TTL eviction.
durabletask-client/src/main/java/io/dapr/durabletask/WorkflowHistoryCache.java	Implements the per-stream committed-history cache with TTL/LRU bounds and byte accounting.
durabletask-client/src/main/java/io/dapr/durabletask/runner/OrchestratorRunner.java	Resolves full committed history using cached prefix + delta or fallback fetch, and updates/evicts cache entries after turns.
durabletask-client/src/test/java/io/dapr/durabletask/WorkItemObserver.java	Adds a gRPC interceptor to count full-sends vs deltas and history fetches for wire-level assertions.
durabletask-client/src/test/java/io/dapr/durabletask/WorkflowHistoryCacheTest.java	Unit tests for cache eviction policies, TTL sliding behavior, and immutability/snapshotting behavior.
durabletask-client/src/test/java/io/dapr/durabletask/StatefulHistoryIT.java	Integration test validating that the sidecar actually sends deltas on the wire and that warm streams avoid cache-miss fetches.
durabletask-client/src/test/java/io/dapr/durabletask/runner/OrchestratorRunnerHistoryTest.java	Deterministic tests for history resolution and cache update behavior in the runner.
durabletask-client/src/test/java/io/dapr/durabletask/IntegrationTestBase.java	Extends test worker builder to accept a custom gRPC channel and toggle stateful history for integration tests.
durabletask-client/src/test/java/io/dapr/durabletask/DurableTaskGrpcWorkerStatefulHistoryTest.java	Worker-level tests against an in-process fake sidecar covering capability advertisement and miss-recovery behavior.

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