main_backend/query_codex.md

The user wants to refactor a backend project following DRY and KISS, keeping it developer-readable without hidden abstractions. The user explicitly rejected a plan that did "in-place cleanup" of cpv3/modules/tasks/service.py and instead wants a different approach.

Currently, tasks/service.py is a 1600+ line monolith that:

1. Defines Dramatiq actors
2. Orchestrates job creation and duplication-checks
3. Has submit_X methods (e.g. submit_media_probe, submit_transcription_generate)
4. Has a giant record_webhook_event that updates the Job state
5. Contains domain-specific artifact saving (e.g. _save_transcription_artifacts, _save_convert_artifacts)
6. Handles cancellation logic.

Constraints:

1. Must use the exact module structure: models.py, schemas.py, repository.py, service.py, router.py (no subdirectories within modules).
2. Explicit, local helpers over hidden abstractions (no generic handler registries).

What is the best architectural approach to distribute these responsibilities across jobs, tasks, and domain modules (media, transcription, captions)? Provide a concrete file-by-file blueprint on where each responsibility belongs and how the cross-module calls would look like, avoiding circular dependencies.