Add NexusOperationHandler annotation

[Quinn-With-Two-Ns]

What was changed

Add NexusOperationHandler annotation that can be used in Nexus Service Handlers on Temporal Workers

Why?

Makes it easier to declare Nexus Service Handlers with less boilerplate

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

Note to reviewers:
nexus-rpc/sdk-dotnet#19 needs to land first and most of the package lock changes are only here to test locally

---

Note

Medium Risk
Touches experimental Nexus registration, hosting DI lifetimes, and bumps NexusRpc to 0.4.0; behavior changes are localized but affect worker startup and operation dispatch paths.

Overview
Introduces [TemporalOperation] so a method on a [NexusServiceHandler] class can be the Nexus operation start handler directly (returning Task<TemporalOperationResult<T>> with TemporalOperationStartContext and ITemporalNexusClient), instead of wiring a [NexusOperationHandler] factory around TemporalOperationHandler.FromHandleFactory. Operations are still matched by method name to the service interface; the attribute cannot be combined with [NexusOperationHandler] on the same method.

TemporalOperationMethodExtension plugs into NexusRpc IMethodExtension (requires NexusRpc 0.4.0). Worker, simple-plugin, and hosting registration now pass this extension into ServiceHandlerInstance.FromInstance. Hosting ServiceHandlerInstanceHelper and ScopedOperationHandler were reworked so both attribute styles resolve handlers per operation, with a fresh DI scope and service instance on each start/cancel for [TemporalOperation] (aligned with activities). Unmatched [NexusOperationHandler] methods fail registration like NexusRpc’s built-in path.

Adds NuGet.Config package-source mapping for the NexusRpc test feed (local testing). Changelog and broad test coverage for validation, execution, DI lifetimes, and mixed handlers.

^{Reviewed by Cursor Bugbot for commit 8483d93. Bugbot is set up for automated code reviews on this repo. Configure here.}

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: f76d3e21a7

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[jmaeagle99]

Small amount of feedback, but looks good overall. Will approve when dependency has been updated.

Side note: this is ripe for source generation, which would create compile-time safe operation registration, but still use the reflection and expression compilation as a fallback. I'm going to log an issue to track this, as there are other areas that can benefit as well.

[jmaeagle99]

Please update CHANGELOG.md with a blurb in the Added section.

[jmaeagle99]

I think the one pitfall of this design is that if a method is attributed with [TemporalOperation] but it's name doesn't match a method in the service interface, then it is silently ignored. This might lead to typo-created mismatches given that the service implementation doesn't implemented the service interface. Not sure what to do with that without given the entire service definition to Temporalio to validate all attributed methods at once. Maybe could be done better with an analyzer.

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{Reviewed by Cursor Bugbot for commit 34d51f1. Configure here.}