fix(api): tolerate missing related users in memo conversions

[boojack]

Summary

• batch-load reaction creators during memo conversion and skip orphaned reactions instead of failing the whole response
• skip memos and memo comments with missing creators in list flows while preserving NotFound behavior for direct lookups and shared memo access
• skip notifications with missing sender or receiver users to prevent a single bad record from breaking the list API
• add regression tests for orphaned memo creators, reaction creators, comment creators, and notification users

Testing

• go test ./server/router/api/v1/test

Summary by CodeRabbit

• Bug Fixes

  • Improved error handling when user creators are deleted; list operations now gracefully skip orphaned memos, comments, reactions, and notifications instead of failing entirely.
  • Updated sharing endpoints to return proper "not found" responses when memo creators are missing.

• Tests

  • Added comprehensive test coverage for scenarios where related user creators have been deleted.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

The PR introduces graceful degradation for missing creators across memo, reaction, comment, and notification entities. Instead of failing requests entirely, services now log warnings, skip orphaned entities, and return successfully with remaining valid data. This includes refactoring batch user-loading logic to minimize database queries when resolving creators.

Changes

Cohort / File(s)	Summary
Memo Service Core Logic server/router/api/v1/memo_service.go, server/router/api/v1/memo_service_converter.go	Added sentinel errors for missing creators (errMemoCreatorNotFound, errReactionCreatorNotFound). Refactored conversion pipeline to batch-load users via listUsersByIDWithExisting, skip orphaned reactions/memos with a warning log instead of failing, and delegate reaction conversion to new convertReactionsFromStoreWithCreators helper.
Dependent Service Updates server/router/api/v1/memo_share_service.go, server/router/api/v1/reaction_service.go, server/router/api/v1/user_service.go	Updated error handling to detect missing-creator sentinel errors and return gRPC NotFound status (memo_share_service) or skip with warning logs (reaction_service, user_service) instead of propagating conversion errors.
Integration Tests server/router/api/v1/test/memo_service_test.go, server/router/api/v1/test/memo_share_service_test.go, server/router/api/v1/test/reaction_service_test.go, server/router/api/v1/test/user_notification_test.go	Added comprehensive test coverage for graceful handling of deleted creators: reactions, memos, comments, and notifications with missing creators are now omitted from responses rather than causing request failures.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix(api): switch user resource names to usernames #5779: Directly modifies the same memo/reaction conversion and user-resolution code paths, including convertMemoFromStore, convertReactionFromStore, and user list/batch-loading helpers.

Poem

🐰 Hops through deleted users with grace,
No more crashing at a missing face,
Warn and skip, let data flow free,
A resilient memo service, huzzah! ✨

🚥 Pre-merge checks | ✅ 3

✅ 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 accurately and concisely summarizes the main change: refactoring the API to handle missing related users gracefully during memo conversions by skipping orphaned entities instead of failing.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch listmemos

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