Implement Mongo Transactions

[imnasnainaec]

This change is 

Summary by CodeRabbit

• Bug Fixes

  • Undo-merge and word-restore now return empty success responses and surface Not Found when unsuccessful.

• New Features

  • Bulk word import support.
  • Expanded frontier merge/replace/revert workflows and richer frontier update/restore/delete behaviors.

• Chores

  • Added transactional DB execution for safer multi-step operations and updated test/mocks to align with new flows.

[github-actions]

⚠️ Commit Message Format Issues ⚠️
commit 095594aa0f:
1: T1 Title exceeds max length (78>72): "Add MongoDB transactions to WordRepository multi-collection operations (#4191)"

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 5106f8bb-2387-46e9-a758-c937446be353

📥 Commits

Reviewing files that changed from the base of the PR and between 78917ae and d8e0f59.

📒 Files selected for processing (3)

• Backend.Tests/Mocks/MongoDbContextMock.cs
• Backend/Contexts/MongoDbContext.cs
• Backend/Interfaces/IMongoDbContext.cs

🚧 Files skipped from review as they are similar to previous changes (1)

• Backend/Interfaces/IMongoDbContext.cs

---

📝 Walkthrough

Walkthrough

Adds MongoDB transaction APIs and tests; refactors word repository toward frontier-focused, transactional operations; shifts many consumers from IWordRepository to IWordService; changes Restore/Undo endpoints to return Ok/NotFound (no boolean payload); updates services, controllers, tests, and frontend typings.

Changes

Cohort / File(s)	Summary
MongoDB transaction infra Backend/Interfaces/IMongoDbContext.cs, Backend/Contexts/MongoDbContext.cs, Backend.Tests/Mocks/MongoDbContextMock.cs	Introduce IMongoDbContext/IMongoTransaction, add Db, BeginTransaction, ExecuteInTransaction/ExecuteInTransactionAllowNull, implement transaction wrapper and test mock.
Word repository core Backend/Interfaces/IWordRepository.cs, Backend/Repositories/WordRepository.cs, Backend.Tests/Mocks/WordRepositoryMock.cs	Replace older CRUD surface with frontier-centric APIs (Restore/Update/Replace/Revert/DeleteFrontier with modifier actions), add transactional/session helpers and complex session-bound operations; mock updated to match new signatures and behaviors.
Word service surface & logic Backend/Interfaces/IWordService.cs, Backend/Services/WordService.cs, Backend.Tests/Services/WordServiceTests.cs	Add Import/MergeReplace/RevertMergeReplace methods, change RestoreFrontierWords→RestoreFrontierWord, centralize timestamp/history helpers, delegate frontier mutations to repository; tests updated and expanded.
Merge flow & API changes Backend/Services/MergeService.cs, Backend/Controllers/MergeController.cs, src/api/api/merge-api.ts, Backend.Tests/Services/MergeServiceTests.cs, src/backend/index.ts	Merge/UndoMerge now call WordService merge/revert APIs; UndoMerge controller returns Ok()/NotFound (no bool); frontend typings and client wrappers updated to void return.
Word controller API Backend/Controllers/WordController.cs, src/api/api/word-api.ts, src/backend/index.ts, Backend.Tests/Controllers/WordControllerTests.cs	RestoreWord now calls service restore directly and returns Ok/NotFound with no boolean payload; frontend types and tests adapted.
Lift import wiring Backend/Interfaces/ILiftService.cs, Backend/Services/LiftService.cs, Backend/Controllers/LiftController.cs, Backend.Tests/Controllers/LiftControllerTests.cs	Change importer/merger APIs to accept IWordService instead of IWordRepository; update controller constructor, service wiring, and tests.
Repositories & transactional refactor Backend/Repositories/WordRepository.cs	Add IMongoDbContext usage, ExecuteWithTransaction helpers and session-bound implementations (Create/Update/Restore/Replace/Revert) to ensure atomic frontier↔words moves.
Tests and mocks Backend.Tests/..., Backend.Tests/Mocks/*	Many tests switched from IWordRepository to WordRepositoryMock, updated assertions/awaits; extensive new tests for import/merge/restore/delete/frontier behaviors; new MongoDbContextMock added.
Startup scope handling Backend/Startup.cs	Resolve repositories from a created async startup scope and dispose the scope after use.
Frontend call changes src/backend/index.ts, src/api/api/*.ts	Frontend wrappers and generated API typings updated to void return types for undoMerge and restoreWord and to stop returning response data.

Sequence Diagram(s)

sequenceDiagram
    participant Client as Client
    participant Controller as Controller
    participant Service as WordService
    participant Repo as WordRepository
    participant DB as MongoDbContext

    rect rgba(200,230,255,0.5)
    Client->>Controller: HTTP restore/undo request
    Controller->>Service: call RestoreFrontierWord / RevertMergeReplaceFrontier
    end

    rect rgba(200,255,200,0.5)
    Service->>Repo: prepare actions (modify/update/replace)
    Repo->>DB: BeginTransaction / ExecuteInTransaction(operation)
    DB-->>Repo: session/transaction wrapper
    Repo->>DB: perform atomic operations across frontier & words
    DB-->>Repo: Commit or Abort
    Repo-->>Service: return result
    end

    Service-->>Controller: Ok / NotFound (no payload)
    Controller-->>Client: HTTP 200/404

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• [WordService] Refactor RestoreFrontierWords #4161 — overlapping changes to frontier restoration and related service/repo methods.
• [TreeView] Add domain count #4046 — related updates to WordRepository and WordRepositoryMock frontier behaviors.
• Fix singleton LiftService dependency on transient repositories #4091 — related Lift import/export wiring changes (IWordRepository → IWordService).

Suggested labels

🟥High

Suggested reviewers

• jasonleenaylor

Poem

🐰 I hopped through sessions, neat and spry,
Frontiers shuffled under a watchful sky.
Bools went quiet, voids took the stage,
Mocks and services tuned the page.
A carrot cheer — commit, hop, and try!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 39.88% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Implement Mongo Transactions' directly and clearly describes the main objective of the changeset—adding transactional capabilities to MongoDB context.

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[codecov]

Codecov Report

❌ Patch coverage is 98.80952% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.24%. Comparing base (c6afad4) to head (d8e0f59).

Files with missing lines	Patch %	Lines
Backend/Controllers/MergeController.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4194      +/-   ##
==========================================
+ Coverage   75.15%   75.24%   +0.09%     
==========================================
  Files         302      302              
  Lines       11099    11092       -7     
  Branches     1394     1386       -8     
==========================================
+ Hits         8341     8346       +5     
+ Misses       2357     2348       -9     
+ Partials      401      398       -3     

Flag	Coverage Δ
backend	86.75% <98.80%> (+0.22%)	⬆️
frontend	66.34% <ø> (ø)

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[imnasnainaec]

@copilot In a new pr on this branch, set up integration testing for WordRepository.

• The tests should spin up actual, minimal instances of a mongo database
• Changes to Backend/ should be minimal and only if necessary
• The integration testing should go in Backend.Tests/, but existing tests in Backend.Tests/ should be unchanged

[Copilot]

@imnasnainaec I've opened a new pull request, #4196, to work on those changes. Once the pull request is ready, I'll request review from you.

[imnasnainaec]

Subsumed in #4198