Fix case-insensitive dedup of action downloads

[stefanpenner]

Summary

• Fixes action deduplication to use case-insensitive comparison for owner/repo names, so actions/checkout and actIONS/checkout are correctly treated as the same action and downloaded only once
• Uses a custom ActionLookupKeyComparer that treats the owner/repo portion of lookup keys case-insensitively while keeping the ref portion case-sensitive (git refs are case-sensitive)
• Normalizes action reference names after dedup lookup (NormalizeRepositoryReference) so that directory paths are consistent on case-sensitive filesystems (Linux)
• Applies across both the batch resolution path and the legacy code path

Fixes #3731

Changes

1. ActionLookupKeyComparer — custom IEqualityComparer<string> for "{owner/repo}@{ref}" keys: name portion is case-insensitive, ref portion is case-sensitive
2. Dedup collections — batch cache dictionary, pending-key set, GroupBy in GetDownloadInfoAsync, and returned download info dictionary all use the new comparer
3. NormalizeRepositoryReference — after dedup lookup, updates each action step's repositoryReference.Name to match the canonical downloadInfo.NameWithOwner, preventing directory mismatches on Linux
4. Regression test — PrepareActions_DeduplicatesCaseInsensitiveActionReferences verifies three differently-cased references resolve once, download succeeds, and references are normalized

Test plan

• New test PrepareActions_DeduplicatesCaseInsensitiveActionReferences passes
• All 36 existing ActionManagerL0 tests pass
• Verify in a live workflow with mixed-case action references (e.g. actions/checkout vs actIONS/checkout) that the action is downloaded only once

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes redundant action resolution/downloads when the same owner/repo@ref is referenced with different casing by switching deduplication to case-insensitive comparisons.

Changes:

• Makes the batch resolution cache and pending-key set case-insensitive.
• Makes GetDownloadInfoAsync dedupe/group and return dictionaries case-insensitive.
• Adds an L0 regression test covering mixed-case references to the same action.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Runner.Worker/ActionManager.cs	Updates action resolution/download deduplication to use case-insensitive keying across caches and GetDownloadInfoAsync.
src/Test/L0/Worker/ActionManagerL0.cs	Adds regression test asserting mixed-case action references resolve only once.

Comments suppressed due to low confidence (1)

src/Runner.Worker/ActionManager.cs:874

• Case-insensitive dedup here changes behavior beyond the API call: DownloadRepositoryActionAsync downloads to a directory derived from ActionDownloadInfo.NameWithOwner, but later PrepareRepositoryActionAsync/LoadAction compute the action directory from the original RepositoryPathReference.Name. On case-sensitive filesystems (Linux), if different-cased references are deduped to a single download, subsequent steps may look in a different (non-existent) directory and fail to find action.yml/Dockerfile. The fix likely needs to also normalize the in-memory RepositoryPathReference.Name (or create an alias directory/symlink) so all references resolve to the downloaded directory.

            // Convert to action reference
            var actionReferences = actions
                .GroupBy(x => GetDownloadInfoLookupKey(x), StringComparer.OrdinalIgnoreCase)
                .Where(x => !string.IsNullOrEmpty(x.Key))
                .Select(x =>
                {
                    var action = x.First();
                    var repositoryReference = action.Reference as Pipelines.RepositoryPathReference;
                    ArgUtil.NotNull(repositoryReference, nameof(repositoryReference));
                    return new WebApi.ActionReference
                    {
                        NameWithOwner = repositoryReference.Name,
                        Ref = repositoryReference.Ref,
                        Path = repositoryReference.Path,
                    };
                })