feat: add FileStore annotation constants

[wangxiaoxuan273]

What this PR does / why we need it

Adds FileStore-specific annotation key constants for digest and unpack indicators used by the File Store implementation.

• FileStoreAnnotations.AnnotationDigest — key for the digest of uncompressed content
• FileStoreAnnotations.AnnotationUnpack — key for indication of unpacking

Includes a test file that validates all constant values.

Which issue(s) this PR resolves / fixes

Part of the File Store implementation split (issue 2 of 10).
Related: #328, #37

Please check the following list

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.76%. Comparing base (5953fb1) to head (8d0c283).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #352   +/-   ##
=======================================
  Coverage   91.76%   91.76%           
=======================================
  Files          64       64           
  Lines        2755     2755           
  Branches      364      364           
=======================================
  Hits         2528     2528           
  Misses        138      138           
  Partials       89       89           

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[Copilot]

Pull request overview

This PR introduces FileStore-specific annotation key constants as part of the File Store implementation. It adds two annotation constants that match the oras-go v2 implementation, maintaining compatibility with the upstream Go library.

Changes:

• Adds FileStoreAnnotations class with two annotation key constants for digest and unpack indicators
• Includes comprehensive unit tests validating the constant values

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/OrasProject.Oras/Content/File/Annotations.cs	Defines FileStore annotation key constants for digest tracking and unpack indication
tests/OrasProject.Oras.Tests/Content/File/AnnotationsTest.cs	Unit tests validating the annotation constant values

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[akashsinghal]

Caution

This review was generated by Copilot using Claude Opus 4.6, mimicking the review style of shizhMSFT. This is not the real shizhMSFT.

Review of PR #352

Verified constants match oras-go (content/file/file.go:52-55) exactly. Two observations:

1. Legacy io.deis.oras prefix (Annotations.cs:25-26, 32-33)

These annotations use the io.deis.oras.content prefix, which is a legacy namespace from when ORAS was part of the Deis project (now deprecated). oras-go carries these for backward compatibility. Since this is the first time the .NET library introduces these constants, it's worth adding a brief XML doc note explaining the provenance — e.g., "This key uses the legacy io.deis.oras prefix for compatibility with oras-go." This prevents a future contributor from "helpfully" renaming the prefix and breaking cross-runtime interop.

2. public visibility for internal-only consumers (Annotations.cs:19)

FileStoreAnnotations is public, but the consuming FileStore class (in oras-go and in the planned .NET implementation per #328) is the only expected user. If the FileStore itself is internal (or not yet implemented), shipping these as public commits to a public API surface that hasn't been exercised yet. Should this be internal until the FileStore is ready for public use? "Public method should return public type" — but the corollary is: don't make types public until you have a public consumer.

Otherwise SGTM — simple, correct, well-tested constants.

[akashsinghal]

@wangxiaoxuan273 can you follow up on the previous AI comment and address them if you feel they are relevant?

[nathana1]

very minor nit: in PR 351 these sort of declarations are on a single line but these are on 2 lines. Is there a standard line length?