feat: support run-based assignments in can-redeem; ensure assigned policies have highest priority

[adamstankiewicz]

Description

Make run-based assignments discoverable in can-redeem

In get_assignment_for_learner, we perform a lookup of assignments based on a top-level course key, even for run-based assignments. Given this, a run-based assignment would never be found. To mitigate, the queryset get now considered the assignment's parent_content_key as well.

Ensuring assignment-based policies have highest priority

When a learner can redeem with both a PerLearnerEnrollmentCreditAccessPolicy and a AssignedLearnerCreditAccessPolicy, the can-redeem API response does not prioritize the assignment-based policy for redemption over other policy types.

The lack of priority for assignment-based policies was noticed when performing stage QA and observed that the learner portal Course page was suggesting the course was assigned (via a badge and the assignment-specific price messaging), but the redemption was attempting to go through the PerLearnerEnrollmentCreditAccessPolicy instead of the expected AssignedLearnerCreditAccessPolicy, not quite matching the UX.

Jira:
N/A

Merge checklist:

• ./manage.py makemigrations has been run
  • Note: This must be run if you modified any models.
    • It may or may not make a migration depending on exactly what you modified, but it should still be run.

Post merge:

• Ensure that your changes went out to the stage instance
• Deploy to prod instance

[pwnage101]

For completeness, should we catch-log-raise the "multiple records returned" exception too? I'm imagining the only time we'd see this is if there's simultaneously a legacy and new assignment for the same course & learner, which shouldn't happen because our business logic should prevent it. That said, explicitly handling the exception might answer any questions from future code readers about why it's not handled.

[adamstankiewicz]

@pwnage101 Updated to include an except block as follows:

except LearnerContentAssignment.MultipleObjectsReturned as exc:
  logger.error(
    f'Multiple assignments found with content_key or parent_content_key {content_key} '
    f'for {assignment_configuration} and lms_user_id {lms_user_id}',
  )
  raise exc

[pwnage101]

LGTM, just nits!