SolutionLockedByAnotherMentorError: SolutionLockedByAnotherMentorError (SolutionLockedByAnotherMentorError)

## Error

```
SolutionLockedByAnotherMentorError (SolutionLockedByAnotherMentorError)
```

## Stack trace

```
app/commands/mentor/request/lock.rb:12 in block in Mentor::Request::Lock#call
active_record/connection_adapters/abstract/transaction.rb:535 in block in ActiveRecord::ConnectionAdapters::TransactionManager#within_new_transaction
active_support/concurrency/null_lock.rb:9 in synchronize
active_record/connection_adapters/abstract/transaction.rb:532 in within_new_transaction
active_record/connection_adapters/abstract/database_statements.rb:344 in transaction
active_record/transactions.rb:212 in transaction
app/commands/mentor/request/lock.rb:7 in call
mandate/call_injector.rb:10 in Mentor::Request::Lock.call
app/controllers/api/mentoring/requests_controller.rb:23 in lock
action_controller/metal/basic_implicit_render.rb:6 in send_action
```

## Tracking Details
- **Project**: exercism-rails
- **Sentry**: [SolutionLockedByAnotherMentorError: SolutionLockedByAnotherMentorError (SolutionLockedByAnotherMentorError)](https://thalamus-ai.sentry.io/issues/97284348/)
- **Culprit**: API::Mentoring::RequestsController#lock
- **First seen:** Feb 17, 2026