Propagate exceptions from command handlers correctly

[avin3sh]

This is to make CommandHandlerInvokerMiddleware correctly 'await' the task before accessing its result, similar to how this is done in RequestHandlerInvokerMiddleware.

Without this change, attempting to access result of a cancelled task would result in TargetInvocationException / AggregateException which breaks the task processing in BackgroundCommandSenderHostedService due to unhandled exception, thus breaking the background queue and particularly in bulk dispatch workflow causing remaining workflows to not get dispatched.

There are also Unit Tests included but they may be overkill for this scenario, can remove.

[avin3sh]

@dotnet-policy-service agree company="D.E. Shaw & Co., L.P."

[sfmskywalker]

Perfect 👍🏻

[Copilot]

Pull request overview

This PR fixes exception propagation in the Elsa.Mediator command pipeline so cancellations/faults from command handlers surface as the original exceptions (instead of TargetInvocationException/AggregateException), preventing background command processing from breaking.

Changes:

• Update CommandHandlerInvokerMiddleware to await the handler task before reading its Result, aligning behavior with the request pipeline.
• Unwrap TargetInvocationException in handler reflection invocations so callers observe the original exception.
• Add new unit tests covering successful execution, cancellation, and failure behavior for commands.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
test/unit/Elsa.Mediator.UnitTests/Elsa.Mediator.UnitTests.csproj	Adds a new unit test project for Elsa.Mediator behavior.
test/unit/Elsa.Mediator.UnitTests/CommandCancellationBehaviorTests.cs	Adds tests verifying command cancellation and exception propagation behavior.
src/common/Elsa.Mediator/Middleware/Command/Components/CommandHandlerInvokerMiddleware.cs	Awaits the invoked task before accessing Result to avoid wrapped exceptions on cancellation/faults.
src/common/Elsa.Mediator/Extensions/HandlerExtensions.cs	Unwraps TargetInvocationException for notification/command handler reflection calls.

[sfmskywalker]

@copilot open a new pull request to apply changes based on the comments in this thread

[sfmskywalker]

@greptile open a new pull request to apply changes based on the comments in this thread

[greptile-apps]

I cannot create a new pull request on your behalf because:

1. You own the branch - PR Propagate exceptions from command handlers correctly #7218 is from your fork (avin3sh/elsa-core) on your branch avin3sh-fix-command-handler-invoker-exception-handling
2. I don't have write access - I can only read from the repository, not create branches or push changes to your fork

To apply the review feedback, you have two options:

Option 1: Update the existing PR (Recommended)
Push additional commits to your branch avin3sh-fix-command-handler-invoker-exception-handling. Here are the changes needed:

1. Fix HandlerExtensions.cs (lines 58 and 79) - Use ExceptionDispatchInfo to preserve stack traces:

using System.Runtime.ExceptionServices;

// At line 58 and 79, replace:
throw ex.InnerException;

// With:
ExceptionDispatchInfo.Capture(ex.InnerException).Throw();

2. Fix CommandCancellationBehaviorTests.cs:

• Line 56: Change to ThrowsAsync<TaskCanceledException> (matches test name)
• Line 83: Dispose the service provider/scope (wrap in using)
• Line 109: Change delay from FromSeconds(10) to FromMilliseconds(500)

Option 2: Ask the PR author
If you're reviewing this PR, ask @avin3sh to apply these changes.

Would you like me to provide the complete corrected code for each file?

[sfmskywalker]

@avin3sh It looks like Copilot can't implement its suggestions because this is a PR from your fork, so it would be great if you could review the suggestions yourself and resolve them (manually or using your own coding agents, of course). Thanks again!

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

[avin3sh]

@sfmskywalker I have made some more changes as per the Agent's suggestions, I don't think the more recent suggestions are very helpful / are scope-creep.

There was a conflict caused by #7226 where ConfigureAwait(false) was introduced in CommandHandlerMiddleware. I did some cleanup and for sake of cosistency/readability ported the same change to RequestHandlerMiddleware too.

Let me know if you think further changes are necessary.

[sfmskywalker]

Looks good to me - thanks for the hard work @avin3sh !