feat(streaming): support stateless worker consumers

[ReubenBond]

Problem

Stateless worker grains currently reject stream consumer extension binding, forcing applications to route stream deliveries through a regular grain before parallel stateless processing.

Solution

• Allow stream consumer extension binding only for stateless workers which implement IStreamSubscriptionObserver.
• Install activation-local observers lazily through OnSubscribed while retaining grain-level implicit and explicit subscription ownership.
• Route concurrent deliveries through normal local stateless-worker selection as competing-consumer work.
• Keep the pulling agent authoritative for live delivery progress by requiring null sequence tokens for stateless worker subscriptions.
• Document locality, ordering, retry, subscription lifecycle, and token semantics.
• Cover implicit and explicit subscriptions, grain-scope unsubscribe, concurrent activation scale-out, and unsupported contracts.

Rationale

Each delivery attempt targets the stateless worker grain identity and executes on one selected local activation. This removes the extra regular-grain hop while preserving provider delivery and retry behavior. Activation-local rewind handshakes are disabled because delivery can move between workers; applications which require checkpoint resume continue to use a regular grain consumer.

Closes #433
Closes #10653

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR updates Orleans streaming to support stateless worker grains as stream consumers (as competing consumers), gated on implementing IStreamSubscriptionObserver, with stateless-worker-specific semantics around activation-local observers and provider-managed progress.

Changes:

• Allow binding StreamConsumerExtension on stateless worker activations only when the grain implements IStreamSubscriptionObserver, and enforce null sequence tokens for those subscriptions.
• Disable rewind/handshake sequence token behavior for stateless worker subscriptions so the pulling agent remains authoritative for live delivery progress.
• Add/expand functional tests plus documentation describing stateless worker delivery locality, ordering, retry, lifecycle, and token rules.

Show a summary per file

File	Description
test/Orleans.Streaming.Tests/StreamingTests/StatelessWorkersStreamTests.cs	Adds functional coverage for explicit/implicit stateless worker consumption, multi-activation concurrency, and invalid contract cases.
test/Grains/TestGrains/StatelessWorkerStreamConsumerGrain.cs	Adds observer-based stateless worker test grains plus shared test state to validate activation-local attachment and concurrency.
test/Grains/TestGrainInterfaces/IStatelessWorkerStreamConsumerGrain.cs	Updates/extends test grain interfaces for explicit subscriptions, unsubscribe, and negative cases.
src/Orleans.Streaming/StreamConsumerGrainContextAction.cs	Adjusts how stream consumer extensions are installed for grains implementing IStreamSubscriptionObserver.
src/Orleans.Streaming/Providers/SiloStreamProviderRuntime.cs	Relaxes the stateless-worker binding restriction specifically for StreamConsumerExtension when the observer contract is implemented, otherwise throws.
src/Orleans.Streaming/Internal/StreamSubscriptionHandleImpl.cs	Adds a flag to disable handshake/sequence token behavior (used for stateless worker subscriptions).
src/Orleans.Streaming/Internal/StreamConsumerExtension.cs	Enforces null sequence tokens for stateless worker subscriptions and passes through handshake-disable behavior.
src/Orleans.Streaming/Hosting/StreamingServiceCollectionExtensions.cs	Ensures activation-created StreamConsumerExtension instances know whether they’re on a stateless worker activation.
src/Orleans.Streaming/Core/IStreamSubscriptionObserver.cs	Clarifies that stateless worker activations receive OnSubscribed per-activation.
docs/site/src/content/docs/streaming/streams-programming-apis.md	Documents stateless worker consumer model, ordering/retry semantics, lifecycle, and token restrictions.
docs/site/src/content/docs/streaming/delivery-semantics.md	Adds ordering note for stateless worker competing-consumer processing across activations.

Review details

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• Files reviewed: 11/11 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

test/Orleans.Streaming.Tests/StreamingTests/StatelessWorkersStreamTests.cs:162

• CreateStreamIdsForDistinctQueues can loop indefinitely if Guid.NewGuid() keeps hashing to queues which are already present. In practice it’s unlikely, but a rare unlucky streak would hang the test run. Consider bounding the search (and failing with a clear message) so the test can’t deadlock CI.

            while (result.Count < PartitionCount)
            {
                var streamId = Guid.NewGuid();
                var queueId = mapper.GetQueueForStream(
                    StreamId.Create(StatelessWorkerStreamConsumerGrain.ExplicitStreamNamespace, streamId));
                result.TryAdd(queueId, streamId);
            }

• Files reviewed: 11/11 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

test/Grains/TestGrains/StatelessWorkerStreamConsumerGrain.cs:3

• using System.Linq; appears unused in this file. With code-style analyzers enabled, unused usings (IDE0005) can fail the build; please remove it (or add the missing LINQ usage if intended).

using System.Collections.Concurrent;
using System.Linq;
using Orleans.Concurrency;

• Files reviewed: 11/11 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

test/Grains/TestGrains/StatelessWorkerStreamConsumerGrain.cs:3

• using System.Linq; appears to be unused in this file (no LINQ APIs are referenced). With analyzers/code-style enforcement, unused usings can fail the build (IDE0005/CS8019). Remove the directive to avoid warnings/errors.

using System.Collections.Concurrent;
using System.Linq;
using Orleans.Concurrency;

• Files reviewed: 11/11 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

test/Grains/TestGrains/StatelessWorkerStreamConsumerGrain.cs:2

• using System.Linq; is unused in this file, which will trigger IDE0005 (and can fail the build when code-style warnings are treated as errors). Remove the directive.

using System.Collections.Concurrent;
using System.Linq;

• Files reviewed: 12/12 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

• Files reviewed: 12/12 changed files
• Comments generated: 1
• Review effort level: Lite