Summary

Closes #1398.

Drop the job-iteration gem dependency in favor of Rails 8.1's built-in ActiveJob::Continuable for cursor-based iteration and resumption. This is a new minor version that bumps the minimum Rails to 8.1 while preserving all existing behavior.

What changed

• Removed job-iteration dependency, replaced include JobIteration::Iteration with include ActiveJob::Continuable
• Rewrote TaskJobConcern to use a single Continuable step :iterate block that handles all collection types
• Added 6 custom enumerator classes replacing job-iteration's enumerator builders:
  • ActiveRecordRecordEnumerator — cursor-based AR record iteration with multi-column/composite PK support
  • ActiveRecordBatchEnumerator — cursor-based AR batch iteration
  • ArrayEnumerator, CsvRowEnumerator, CsvBatchEnumerator, OnceEnumerator
• Added MaintenanceTasks.max_job_runtime config (default 5 minutes) replacing JobIteration.max_job_runtime
• Two interruption paths preserved:
  • Queue stopping → Continuable's Interrupt exception → auto re-enqueue via retry_job
  • App stopping (pause/cancel) → @run.stopping? check → manual state persistence
• Bumped minimum Rails from 7.1 to 8.1
• Removed Rails 7.x/8.0 CI gemfiles
• Updated README references

Key design insight

ActiveJob::Continuation::Interrupt inherits from Exception (not StandardError), so the existing rescue_from StandardError error handling flows through cleanly without conflicting with Continuable's interrupt mechanism.

checkpoint! override

Continuable's checkpoint! directly checks queue_adapter.stopping?. To support max_job_runtime, we override checkpoint! on the class level (inside the included block) to also check elapsed time. This is necessary because ActiveJob::Continuable sits above TaskJobConcern in the MRO when included in the included block.

Test plan

• All 288 existing unit/integration tests pass
• RuboCop clean (0 offenses)
• System tests pass
• Verify pause/resume cycle works end-to-end
• Verify CSV task with cursor resumption
• Verify multi-column cursor AR tasks
• Verify throttled tasks back off and re-enqueue