show helpful error message when resolving actions directly with launch

[aiqiaoy]

Related: https://github.com/github/actions-runtime/issues/5135

Before:

vs. After:

actions-dotnet implementation: https://github.com/github/actions-dotnet/blob/f9322e925c9f23d04fb974295604864fd4a195cc/Launch/Sdk/Server/LaunchApi.cs#L87-L98

[Copilot]

Pull Request Overview

This PR introduces a feature flag (DisplayHelpfulActionsDownloadErrors) to toggle enhanced error messages when resolving action download info via the launch service, adds a new V2 API surface with richer error handling (422/429), and updates the worker and tests to exercise the new behavior.

• Add DisplayHelpfulActionsDownloadErrors flag and overloads in ILaunchServer/LaunchServer & ActionManager
• Extend LaunchHttpClient with GetResolveActionsDownloadInfoAsyncV2 for custom 422/429 handling
• Add L0 tests for success and unprocessable-entity error paths in the new client

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Runner.Common/Constants.cs	Introduce DisplayHelpfulActionsDownloadErrors feature flag
src/Runner.Common/LaunchServer.cs	Add overload for ResolveActionsDownloadInfoAsync
src/Runner.Worker/ActionManager.cs	Wire feature-flag into launchServer.ResolveActions... call
src/Sdk/WebApi/WebApi/LaunchHttpClient.cs	Implement GetResolveActionsDownloadInfoAsyncV2 with 422/429
src/Sdk/WebApi/WebApi/LaunchContracts.cs	Add data contracts for resolution errors
src/Test/L0/Worker/ActionManagerL0.cs	Update mock to include new boolean parameter
src/Test/L0/Sdk/LaunchWebApi/LaunchHttpClientL0.cs	New tests for success and 422 error cases

Comments suppressed due to low confidence (3)

src/Test/L0/Sdk/LaunchWebApi/LaunchHttpClientL0.cs:77

• Add a unit test for the HTTP 429 (TooManyRequests) path to ensure NonRetryableActionDownloadInfoException is thrown with the expected message.

[Fact]

src/Sdk/WebApi/WebApi/LaunchHttpClient.cs:40

• [nitpick] Consider renaming GetResolveActionsDownloadInfoAsyncV2 to something more descriptive (e.g. GetResolveActionsDownloadInfoWithErrorsAsync) to clarify its behavior and avoid version suffixes in public API names.

public async Task<ActionDownloadInfoCollection> GetResolveActionsDownloadInfoAsyncV2(Guid planId, Guid jobId, ActionReferenceList actionReferenceList, CancellationToken cancellationToken)

src/Runner.Common/LaunchServer.cs:18

• This interface change is breaking for implementers. Consider adding a default-valued overload or a non-breaking extension method rather than modifying the existing signature.

Task<ActionDownloadInfoCollection> ResolveActionsDownloadInfoAsync(Guid planId, Guid jobId, ActionReferenceList actionReferenceList, CancellationToken cancellationToken, bool displayHelpfulActionsDownloadErrors);