Running Resumable Sync Jobs

A sync job is a loop over N items against a service that will fail partway through. Everything hard about these jobs is what happens on item K of N: what the process reports, what it wrote down, and what the next run does with that. Get the happy path right and you still ship a job that silently under-collects, double-applies, or bills for work it never did.

The exit code is the only thing automation reads

The most common failure: per-item errors are printed as warnings, the loop continues, and the run finishes by saving state, committing, printing "Sync complete!" and returning success. A cron wrapper, a CI step, or a supervisor sees exit 0 and reports a healthy job forever.