Report infra_error for action download failures.

[TingluoHuang]

Make sure we know that download actions are failing for whatever reason, help identify and investigate server-side problem easier.

[Copilot]

Pull request overview

Adds explicit infrastructure error reporting for action download failures so runner logs/telemetry can better distinguish download issues from other action preparation problems.

Changes:

• Introduces FailedToDownloadActionException in DTWebApi exception set.
• Wraps non-cancellation download failures in DownloadRepositoryArchive with FailedToDownloadActionException.
• Catches FailedToDownloadActionException in PrepareActionsAsync and reports an InfrastructureError with a new category.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Sdk/DTWebApi/WebApi/Exceptions.cs	Adds a new serializable FailedToDownloadActionException type for propagating download failures with an inner exception.
src/Runner.Worker/ActionManager.cs	Wraps download failures and reports them as infrastructure issues during action preparation.

Comments suppressed due to low confidence (1)

src/Runner.Worker/ActionManager.cs:1263

• DownloadRepositoryArchive now wraps all non-cancellation exceptions in FailedToDownloadActionException. This includes ActionNotFoundException (404) which previously bubbled up as a user/action configuration error (and is covered by existing L0 tests). Wrapping it will reclassify 404s as infrastructure failures (via the PrepareActionsAsync catch) and changes the thrown exception type/behavior.

Consider excluding ActionNotFoundException (and any other intentionally-surfaced exceptions) from this wrapper, e.g. by adding a dedicated catch/rethrow before this catch, or by refining the exception filter to skip those types.

            catch (Exception ex) when (!(ex is OperationCanceledException) && !executionContext.CancellationToken.IsCancellationRequested)
            {
                Trace.Error($"Failed to download archive '{downloadUrl}' after {retryCount + 1} attempts.");
                Trace.Error(ex);
                throw new FailedToDownloadActionException($"Failed to download archive '{downloadUrl}' after {retryCount + 1} attempts.", ex);
            }

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