feat(actors): add configurable Proto.Actor Pub/Sub subscriber storage

[DenDeline]

Summary

Make Proto.Actor Pub/Sub subscriber storage configurable and persistent across topic reactivation, with an optional Redis-backed provider for clustered deployments.

Fixes #169.

Changes

• Add CreatePubSubSubscribersStore to ProtoActorFeature.
• Register one stable subscriber store per service provider/member.
• Explicitly register exactly one TopicActor.Kind, while preserving existing manual store and topic-kind registrations.
• Resolve the store lazily when a topic actor is produced.
• Provide a process-local in-memory default that survives topic reactivation on the same host.
• Add the optional Elsa.Actors.ProtoActor.PubSub.Redis module with protobuf serialization, configurable database resolution, key prefix, and complete key formatter.
• Document that clustered members must share the same durable Redis database and deterministic key configuration.
• Add focused coverage for DI lifetime, lazy resolution, compatibility, serialization, key generation, feature composition, and cancellation.

Compatibility

This is additive. Existing IKeyValueStore<Subscribers> or manual TopicActor.Kind registrations remain authoritative. The core Proto.Actor package does not gain a Redis dependency.

The default store is process-local only; it does not survive process restarts or cross-member migration. Clustered deployments should configure shared durable storage.

Validation

• dotnet test test/modules/actors/Elsa.Actors.ProtoActor.UnitTests/Elsa.Actors.ProtoActor.UnitTests.csproj --configuration Release --no-restore: 23 passed.
• dotnet build src/modules/actors/Elsa.Actors.ProtoActor.PubSub.Redis/Elsa.Actors.ProtoActor.PubSub.Redis.csproj --configuration Release --no-restore: .NET 8, 9, and 10 succeeded with zero warnings and zero errors.
• dotnet list ... package --vulnerable --include-transitive --no-restore: no vulnerable packages.
• git diff --check origin/main...HEAD: passed.

Review status

Greptile verified one P2 cancellation issue on the earlier head. Contributor commit 391bca3 fixed it, current head 5e3eaa7 adds regression tests, and the review thread has a direct maintainer reply. Greptile then explicitly declined current-head review because the contributor is outside its author allowlist, so the historical score is not reused. Worker self-review and root current-head review found no remaining actionable issue. Fresh GitHub CI remains the merge gate.

Scope

This PR covers subscriber-store configuration, the process-local default, the optional Redis provider, and focused tests. It does not change cluster lifecycle, member-local cache invalidation, or protobuf remote registration, which were delivered separately in #168, #174, and #171.

[DenDeline]

For easier review, this comparison shows only this PR’s changes and excludes dependency #168: review the focused diff. It contains one commit across 13 files

[sfmskywalker]

@greptileai

[greptile-apps]

Greptile Summary

This change makes Proto.Actor Pub/Sub subscriber persistence configurable and adds an optional Redis-backed store with configurable key generation. Direct execution confirmed that the in-memory store applies reads and state changes even when its cancellation token is already canceled. Add cancellation guards before merge so aborted operations cannot update subscriber state.

Confidence Score: 4/5

Not merge-safe until canceled subscriber-store operations stop reading or mutating state.

One verified non-security P2 finding remains. Under the scoring rules, a nonempty set containing only P2 findings scores 4.

Files Needing Attention: src/modules/actors/Elsa.Actors.ProtoActor/Services/InMemorySubscribersStore.cs

T-Rex Logs

What T-Rex did

• T-Rex produced a proof for the posted P2 finding and linked it to the review comment.
• T-Rex executed the cancellation harness to exercise the subscriber-store path described in the finding and began validating the observed behavior.
• A baseline subscriber-store behavior log was captured to establish the expected execution flow.
• A canceled-token subscriber-store behavior log was captured to compare against the baseline and verify the impact of cancellation.
• Artifacts were uploaded and organized for reviewer inspection, including the executable cancellation harness source and the two behavior logs.

_{Ran code and verified through T-Rex}

Prompt To Fix All With AI

### Issue 1
src/modules/actors/Elsa.Actors.ProtoActor/Services/InMemorySubscribersStore.cs:11-26
**Canceled operations still mutate in-memory subscriber state**

`InMemorySubscribersStore` accepts a `CancellationToken` but never observes it. A canceled `SetAsync` replaces the stored subscribers and a canceled `ClearAsync` removes them instead of throwing before any state change. This differs from the Redis implementation and allows shutdown or aborted Pub/Sub operations to commit changes after their caller has canceled them. Call `ct.ThrowIfCancellationRequested()` at the start of each store operation.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "Add configurable Pub/Sub subscriber stor..." | Re-trigger Greptile}

[greptile-apps]

PR author is not in the allowed authors list.

[sfmskywalker]

Reviewed current head 5e3eaa7 against issue #169 and current main. The scoped DI registration, lazy TopicActor store resolution, manual-registration preservation, Redis package boundary, cancellation behavior, and regression coverage are coherent. Independent validation passes 23/23 focused tests, .NET 8/9/10 builds, vulnerability scan, and diff check.