**Enhancement: add grading retries with backoff for external evaluation providers**

[MaryammAli]

• Description: External graders occasionally fail transiently and should be retried with controlled backoff rather than immediately failing submissions.
  • Impacted files: BackendAcademy/src/challenges/challenges.service.ts, BackendAcademy/src/jobs/jobs.service.ts, BackendAcademy/src/config/env.schema.ts, BackendAcademy/src/notifications/notifications.service.ts

[eulami]

@eulami has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi. I am conversant with these kind of issues and can deliver a good PR within 24 hours. Kindly assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @eulami to this issue.

[Caneryy]

@Caneryy has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello! Can I work on this issue please?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Caneryy to this issue.

[drips-wave]

Congratulations, @eulami! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @eulami: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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