Allow getting a word from the Frontier

[imnasnainaec]

Important piece of #4146 (though the payoff of this pr alone is small)

Purpose: Without this, whenever we want a frontier word, it requires a 2-part operation: getting the word from WordsCollection then confirming that it's in FrontierCollection.

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This change is 

Summary by CodeRabbit

• Bug Fixes

  • Made frontier lookups consistent across audio upload, deletion, and duplicate handling to prevent incorrect audio associations and assertion failures.

• Refactor

  • Split frontier access into a bulk retrieval and a targeted lookup to clarify list vs single-item behavior and improve data consistency.

• Tests

  • Updated tests and mocks to align with the revised frontier retrieval patterns and ensure assertions reflect the new behavior.

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📝 Walkthrough

Walkthrough

Renamed the repository bulk frontier method to GetAllFrontier(projectId), added a single-item GetFrontier(projectId, wordId, audioFileName?), and updated controllers, services, repository, tests, and mocks to use the new API surface and nullable single-word semantics.

Changes

Cohort / File(s)	Summary
Interface & Repository Backend/Interfaces/IWordRepository.cs, Backend/Repositories/WordRepository.cs	Removed old GetFrontier(projectId) list method; added GetAllFrontier(projectId) (bulk) and GetFrontier(projectId, wordId, audioFileName?) (single, nullable); repository implements both.
Controllers Backend/Controllers/WordController.cs, Backend/Controllers/AudioController.cs	List retrievals switched to GetAllFrontier(...); single-word lookups now call GetFrontier(projectId, wordId, ...) instead of prior GetWord/old variants.
Services Backend/Services/... LiftService.cs, MergeService.cs, StatisticsService.cs, WordService.cs, MergeService.cs	Internal calls updated from GetFrontier(projectId) to GetAllFrontier(projectId); WordService and other flows use GetFrontier(...) for targeted lookups and handle nullable results.
Tests Backend.Tests/Controllers/..., Backend.Tests/Services/... Backend.Tests/Controllers/AudioControllerTests.cs, Backend.Tests/Controllers/WordControllerTests.cs, Backend.Tests/Services/MergeServiceTests.cs, Backend.Tests/Services/WordServiceTests.cs	All test call sites changed to GetAllFrontier for lists and to GetFrontier overload for single lookups; assertions adjusted to reflect renamed APIs and nullable single-item semantics.
Test Mocks Backend.Tests/Mocks/WordRepositoryMock.cs	Mock renamed bulk method to GetAllFrontier, added single-item GetFrontier(projectId, wordId, audioFileName?), and renamed related delay/call-count fields and setters.
Other Backend.Tests/..., other touched files	Consistent renames and minor refactors across codebase to align with new frontier API signatures and usages.

Sequence Diagram(s)

sequenceDiagram
  participant Client as Client
  participant Ctrl as Controller
  participant Svc as Service
  participant Repo as Repository

  Client->>Ctrl: Request frontier list
  Ctrl->>Svc: GetAllFrontier(projectId)
  Svc->>Repo: GetAllFrontier(projectId)
  Repo-->>Svc: List<Word>
  Svc-->>Ctrl: List<Word>
  Ctrl-->>Client: 200 OK (list)

  Client->>Ctrl: Request single frontier word (with optional audio)
  Ctrl->>Svc: GetFrontier(projectId, wordId, audioFile?)
  Svc->>Repo: GetFrontier(projectId, wordId, audioFile?)
  Repo-->>Svc: Word? (nullable)
  Svc-->>Ctrl: Word or NotFound
  Ctrl-->>Client: 200 OK / 404 NotFound

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• jasonleenaylor

Poem

🐇 I hopped through code with a twitch and a grin,

One call to fetch many, one call to pin.
Tests tidied up, mocks learned the new dance,
Frontier split fine — give this change a chance.
🥕✨

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 35.29% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Allow getting a word from the Frontier' accurately describes the main change: introducing new GetFrontier and GetAllFrontier methods to retrieve words directly from the Frontier rather than using the previous GetWord method.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into master

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch word-repo-get-frontier

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[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.12%. Comparing base (bbbdacf) to head (363b527).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
Backend/Services/MergeService.cs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4148       +/-   ##
===========================================
+ Coverage   74.76%   86.12%   +11.36%     
===========================================
  Files         302       56      -246     
  Lines       11068     4829     -6239     
  Branches     1389      599      -790     
===========================================
- Hits         8275     4159     -4116     
+ Misses       2390      524     -1866     
+ Partials      403      146      -257     

Flag	Coverage Δ
backend	86.12% <92.85%> (ø)
frontend	?

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[jasonleenaylor]

Am I missing a test that uses the new GetFrontier implementation?
I saw the mock was added but I don't think there are any tests which call GetFrontier.

@jasonleenaylor reviewed 12 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec).

[jasonleenaylor]

@jasonleenaylor reviewed 3 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec).