Handle Windows local-view collapse for case-sensitive repositories

[woutervanranst]

Problem

Arius should be able to browse and restore repositories created on case-sensitive platforms such as Linux, even when the user is running on Windows.

The repository model should keep repository-relative paths case-sensitive. The harder problem is the local filesystem merge/view on Windows, where the host filesystem is case-insensitive and may collapse paths that are distinct in the repository (for example Foo.txt and foo.txt).

This should not be fixed by making repository path identity case-insensitive in unrelated flows such as hydration-status lookups.

Why this matters

We need a clear and correct boundary between:

• repository identity: case-sensitive, platform-native to the archived repository
• Windows local view: case-insensitive collapse of the host filesystem state
• restore pipeline: responsible for handling Windows conflicts when restoring case-distinct repository paths onto a case-insensitive filesystem

Without that separation, Explorer/listing behavior can silently misrepresent local state or hide repository distinctions.

Areas to investigate

• ListQueryHandler local/cloud merge behavior
• LocalFileSnapshotBuilder keying and collision behavior
• RelativeFileSystem enumeration on Windows
• Explorer presentation of repository entries that differ only by case
• Restore conflict behavior for case-distinct repository paths on Windows

Questions to answer

• How should Explorer present a Linux-native repository containing paths that differ only by case when running on Windows?
• How should the local filesystem view collapse or annotate case-colliding paths?
• What invariants should be preserved between list, Explorer, and restore behavior?
• Which layer should detect and surface Windows-only conflicts?

Acceptance criteria

• Repository-relative paths remain case-sensitive in domain logic.
• Windows local-state merge behavior is explicitly defined for case-colliding paths.
• Explorer/list behavior is covered by focused tests for case-sensitive repository entries on Windows.
• Restore behavior for case-distinct repository paths on Windows is documented and/or covered by tests.

[woutervanranst]

Follow-up from review investigation:

The hydration-status lookup comments appear unrelated to this issue. ChunkHydrationStatusQueryHandler currently returns file.RelativePath from the query unchanged, so that path correlation is not where Windows/local case-collapsing happens.

The more likely current collapse points are in the local merge layer:

• src/Arius.Core/Features/ListQuery/LocalFileSnapshotBuilder.cs
  • BuildFiles() stores local files in Dictionary<PathSegment, LocalFileState>
  • binary entries assign via files[file.Path.Name] = ...
• src/Arius.Core/Features/ListQuery/ListQueryHandler.cs
  • BuildLocalDirectorySnapshot() stores local directories in Dictionary<PathSegment, LocalDirectoryState>

That looks like the right area to define and test Windows behavior when the repository contains case-distinct entries such as Foo.txt and foo.txt, while the local filesystem view may collapse them.