VersionError during cron should not cause cron to halt / crash

[Alys]

As described at #10806 (comment) and in #10711, if a VersionError occurs while cron is processing Dailies or Habits, cron will stop prematurely.

That should not happen. Cron should either:

• ignore the error (leave the Daily unprocessed) and continue with the other Dailies and other kinds of actions
• repeat its handling of that Daily, and then continue on to all other Dailies and other kinds of actions.

I'll leave this as suggestion-discussion for a few days in case staff have any comments and then mark it as help wanted.

[paglias]

With PR #12335 the Habitica codebase has been updated to support MongoDB 4.2 and transactions making it possible to fix this issue.

Transactions allow operations on multiple documents to be executed ensuring that either all of them are executed correctly or none, making it possible to fix this issue.

An example on using transactions can be found at https://mongoosejs.com/docs/transactions.html while more info at https://docs.mongodb.com/manual/core/transactions/. If you want to work on this issue and have any question please leave a comment!

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This may be fixed by using transactions and wrapping everything that happens at cron in a transaction but we should make sure that if cron gets completely reverted the website and apps will give the user another chance to cron without the RYA model being shown twice. Also given how many parts of the code cron touches it might require a very big refactoring to use transactions when scoring tasks, ...