feat: course authoring automatic migration

[BryanttV]

Closes: #223

Description

This PR implements the automatic course authoring migration feature, which triggers a migration between the legacy CourseAccessRole system and the new AuthZ (Casbin-based) system whenever the authz.enable_course_authoring waffle flag is toggled for a course or organization.

Changes

New Model: AuthzCourseAuthoringMigrationRun

• Tracks the full lifecycle of each migration run (forward or rollback).
• Supports the following statuses: running, completed, partial_success, failed, skipped.
• Scopes can be course or org.
• Enforces a database-level uniqueness constraint to prevent concurrent runs for the same scope.
• Stores structured metadata (success/error counts, error details, skip reasons) as JSON.

New Core Function: run_course_authoring_migration

• Orchestrates a full migration run with tracking and concurrency protection.
• Uses transaction.atomic() to create the tracking record atomically. An IntegrityError from the unique constraint skips the run instead of crashing.
• Delegates to migrate_legacy_course_roles_to_authz (forward) or migrate_authz_to_legacy_course_roles (rollback).
• Unhandled exceptions mark the run as failed (outside the inner transaction, so the tracking record is always persisted).

Signal Handlers

• Connects post_save signals from WaffleFlagCourseOverrideModel and WaffleFlagOrgOverrideModel.
• handle_course_waffle_flag_change / handle_org_waffle_flag_change → delegate to trigger_course_authoring_migration.
• trigger_course_authoring_migration:
  • Guards against execution when ENABLE_AUTOMATIC_AUTHZ_COURSE_AUTHORING_MIGRATION = False.
  • Ignores saves for unrelated waffle flags.
  • Detects no-op saves (flag value didn't actually change) by comparing against the previous record.
  • Determines migration direction: FORWARD when flag is enabled, ROLLBACK when disabled.

New Setting

• ENABLE_AUTOMATIC_AUTHZ_COURSE_AUTHORING_MIGRATION defaults to False. Must be explicitly opted in to activate automatic migrations.

Testing Instructions

• To populate the environment with test data, you can use the following scripts.zip
• Create the waffle flag at the course or organization level.
• Toggle the state between enabled/disabled.
• Verify the new record in the tracking model.

Related PR

• docs: add ADR for course authoring automatic migration #251

Merge checklist

Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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[BryanttV]

Note to the reviewer:

I was running tests to verify that the UniqueConstraint was working, but it wasn’t. After investigating a bit, I found that in MySQL, the conditions are ignored because they are not supported ^{1 2}. Therefore, I implemented validation by overriding the save() method, preventing the creation of additional records with the same scope_type and scope_key if one already exists in a running state.

Footnotes

1. https://docs.djangoproject.com/en/5.2/ref/models/constraints/#django.db.models.UniqueConstraint.condition ↩

2. https://docs.djangoproject.com/en/5.2/ref/models/indexes/#django.db.models.Index.condition ↩

[dwong2708]

Impressive work. Just a couple of comments. Thanks!

[mariajgrimaldi]

Thanks a lot for all the effort!

[rodmgwgu]

Thanks for all this work!

[dwong2708]

LGTM! Great job on this.

[mariajgrimaldi]

LGTM!

Let's not forget to document this thoroughly for operators ;) thanks all!