fix(compute_worker): make submission lifecycle idempotent against bro…

[AybH26]

Closes #2433

Summary

compute_worker uses task_acks_late = True, so any worker that dies before acking causes RabbitMQ to redeliver the run payload. The redelivered worker used to re-execute the full lifecycle, with three visible consequences:

1. scoring_worker_hostname was overwritten by the second worker.
2. The submission status was flipped backwards through Running → Scoring → Finished again.
3. upload_submission_scores inserted a second SubmissionScore row per leaderboard column, which then crashed Submission.calculate_scores() with MultipleObjectsReturned.

This PR makes the lifecycle idempotent on both sides of the wire (defense-in-depth, Stripe-style: worker short-circuits, server refuses to double-mutate).

What changed

Worker

• compute_worker/compute_worker.py — run_wrapper now probes GET /api/submissions/<id>/worker_state/ on entry. If the submission is already terminal it logs the redelivery and returns {"skipped": True}, letting Celery ack the message. New Run._fetch_submission_state helper is best-effort — any API error falls through to the legacy path so a transient blip cannot block a legitimate run.

API

• src/apps/api/views/submissions.py
  • New @action worker_state on SubmissionViewSet: authenticated by the submission secret query param, returns {status, is_terminal, has_scoring_result, has_prediction_result, worker_attempt_count}, atomically bumps the counter via F('worker_attempt_count') + 1.
  • check_object_permissions no longer writes ingestion_worker_hostname / scoring_worker_hostname once the row is terminal.
  • upload_submission_scores upserts one SubmissionScore per (submission, column) instead of blindly creating duplicates.
• src/apps/api/serializers/submissions.py — SubmissionCreationSerializer.update refuses status mutations on terminal rows (returns 200 OK with the unchanged instance so the redelivered worker acks cleanly).

Model

• src/apps/competitions/models.py — new Submission.worker_attempt_count field for the audit trail.