feat: add endpoint to delete or archive a CompetencyCriterion (#674)

docs/openedx_learning/decisions/0002-competency-criteria-model.rst

@@ -108,7 +108,7 @@ Decision
 
    Boundaries and intended behavior:
 
-   - Empty groups: Persisted criteria definitions should not contain empty groups. Authoring flows may temporarily create empty groups while editing, but backend validation must reject them.
+   - Empty groups: Persisted criteria definitions should not contain empty groups. Authoring flows may temporarily create empty groups while editing. The criterion delete path enforces this rule for the groups it empties: such a group is deleted, or archived when learner progress references it or when only archived children remain, in the same transaction, so that path persists no empty group. Writers outside this path are not covered by it.
    - Mixed tree depths: Backend supports deeply nested groups. Current frontend authoring constraint is a maximum depth of 3 layers total, using zero-indexed depth (``0=root``, ``1=course-scope group``, ``2=leaf criteria/group``).
    - Retrieval scope: A read always includes the root group, plus any selected subset of course-scoped groups, each returned as a complete subtree, never truncated.
    - Practical size and growth: Total rows in ``CompetencyCriteriaGroup`` are expected to grow over time as course runs are added; this ADR sets no global DB row cap. No max total node-count cap is required per root group. Each course-scoped subtree is expected to stay small (realistically <=500 nodes).
@@ -311,7 +311,7 @@ Decision
 
    - If no related row exists in ``StudentCompetencyCriteriaStatus`` (the leaf-level learner status table, Decision 6) for a competency definition, delete behaves as it does today: a hard delete that cascades through competency metadata tables.
    - Once a related row exists in ``StudentCompetencyCriteriaStatus``, deletion of the associated competency definition row still succeeds, but as an archive (soft delete) instead of a hard delete: the row is hidden from authoring and new associations but remains queryable, so existing learner status rows stay resolvable. This archive-vs-hard-delete rule applies to ``oel_tagging_tag``, ``oel_tagging_taxonomy``, ``CompetencyTaxonomy``, ``oel_tagging_objecttag``, ``CompetencyCriteriaGroup``, and ``CompetencyCriteria``; see :ref:`openedx-learning-adr-0003` Decision 3 for ``oel_tagging_objecttag``'s own archive rule and traceability exception.
-   - ``StudentCompetencyCriteriaStatus`` is what determines whether a record is protected. ``StudentCompetencyCriteriaGroupStatus`` and ``StudentCompetencyStatus`` are roll-up tables derived from it (Decision 6) and are not independently checked for this purpose: :ref:`openedx-learning-adr-0004` writes the leaf table synchronously with the grade but rolls the two roll-up tables up later via an asynchronous task, which can lag behind the leaf or, per that ADR's Decision 5, need manual recovery. Checking only the roll-up tables could therefore miss real learner progress that has not rolled up yet.
+   - ``StudentCompetencyCriteriaStatus`` is what determines whether a record is protected. ``StudentCompetencyCriteriaGroupStatus`` and ``StudentCompetencyStatus`` are roll-up tables derived from it (Decision 6) and are not independently checked for this purpose, with one exception: the criterion delete cascade checks ``StudentCompetencyCriteriaGroupStatus`` directly before hard-deleting a group, because a group row about to be deleted cannot wait for the roll-up to catch up. :ref:`openedx-learning-adr-0004` writes the leaf table synchronously with the grade but rolls the two roll-up tables up later via an asynchronous task, which can lag behind the leaf or, per that ADR's Decision 5, need manual recovery. Checking only the roll-up tables could therefore miss real learner progress that has not rolled up yet.
    - Direct deletion of a ``CompetencyRuleProfile`` is never a hard delete; retirement is always archive-only, via a normal update to its ``archived`` column (Decision 3). However, if a taxonomy or course that is associated with a taxonomy- or course-scoped profile is deleted, then this profile will be deleted along with it.
    - For MVP, archiving a ``CompetencyCriteriaGroup`` or a ``CompetencyCriteria`` row is permanent, with one exception: an archived root ``CompetencyCriteriaGroup`` is reactivated when a new criterion is added for its competency (Decision 2). ``oel_tagging_objecttag`` follows :ref:`openedx-learning-adr-0003` Decision 3 instead.
 
@@ -490,3 +490,10 @@ Changelog
   supersedes the ordered, short-circuited evaluation the earlier text described. Decision 6's update flow now continues past the root group to the
   competency's own status row and up through parent competencies, and states what a
   competency with no criteria tree of its own receives.
+
+2026-11-04:
+
+* Amended Decisions 2 and 7 for issue #674: the criterion delete cascade, not a backend validation
+  rejection, keeps the groups it empties out of the database, and it checks
+  ``StudentCompetencyCriteriaGroupStatus`` directly before hard-deleting a group, as #674's
+  acceptance criteria require.

docs/openedx_learning/decisions/0003-competency-criteria-versioning.rst

@@ -35,7 +35,7 @@ For the initial implementation, versioning and traceability of competency achiev
 
    - Before any related learner status exists, edits and deletes are allowed.
    - After any related learner status exists, disassociation/deletion is archive-only (soft delete), not hard delete.
-   - Ordinary reads (tag lists, object-tag-for-an-object lookups used by authoring UIs, and similar) exclude archived rows, so an archived association behaves as gone from those paths.
+   - Ordinary reads (tag lists, object-tag-for-an-object lookups used by authoring UIs, and similar) exclude archived rows, so an archived association behaves as gone from those paths. For MVP, one exception applies: the ``ObjectTag`` of a criterion archived by the delete endpoint stays live, so the competency tag remains visible on the tagged object while the criterion itself is closed to authoring.
    - The read path that resolves a learner status row back to the ``ObjectTag`` it references is exempt from that exclusion: archived rows remain queryable on that path, so learner status records can continue to be traced back to their source association.
 
 4. Authoring guardrails must warn on potentially impactful edits:
@@ -128,3 +128,11 @@ Rejected Alternatives
 11. Drop the database-level foreign key constraint on the learner column.
      - Cons:
          - This repo's convention is a real foreign key to ``settings.AUTH_USER_MODEL``. Reports of contention on the user row exist elsewhere in the ecosystem, but are not understood well enough here to design around.
+
+Changelog
+---------
+
+2026-11-04:
+
+* Amended Decision 3 for issue #674: the ``ObjectTag`` of a criterion archived by the delete endpoint stays live for MVP,
+  so the competency tag remains visible on the object.

docs/openedx_learning/decisions/0004-competency-mastery-concurrency.rst

@@ -68,7 +68,9 @@ Decision
    rows above it are recalculated and overwritten rather than merged. A later grade change can raise
    what an edit lowered, but never lower what an edit raised.    The staff correction takes a row lock
    on the ``StudentCompetencyCriteriaGroupStatus`` row for that learner and the competency's root
-   criteria group, the group with no parent; no other path takes a lock.
+   criteria group, the group with no parent; no other learner-status writer takes a lock. Criterion
+   authoring writers (create, delete, bulk update, and group update) serialize per competency on
+   the competency's ``Tag`` row, each taking that lock first and no other explicit locking read on groups or criteria.
 
 
 
@@ -162,3 +164,11 @@ Rejected Alternatives
           before the write completes.
         - It also only checks for a race at the moment each parent is read. If the worker crashes mid-cascade before reaching the next read,
           nothing notices the rollup was left unfinished. Decision 5's manual recovery mechanism exists to catch that case.
+
+Changelog
+---------
+
+2026-11-04:
+
+* Amended Decision 6 for issue #674: the rule that no other path takes a lock covers learner-status
+  writers only. Criterion authoring writers serialize per competency on the ``Tag`` row.