WR-07: when storing the grader's score fails on the last River attempt,
record the answer as failed instead of leaving it pending with no job.
The terminal failure write runs on a context detached from the job's,
so a timed-out or cancelled job still records it.
WR-06: a Question save hook clears grading_status on the answers of a
question that changed type away from open, in the save's transaction,
so they leave the review queue and needs_review. GradeAnswer ignores a
question that is no longer open, and a choice or self-check re-answer
clears the text, grade and review columns of its row.
WR-01: a deterministic server-side guard behind the grader's prompt.
storeGrade drops feedback sharing a run of six words with the rubric
(runs also in the question or model answer do not count) and notes it
for the owner in grading_error.
- graders registry collected at boot from every HasGraders plugin,
manual first; a duplicate or reserved code fails boot
- grading job on queue quizzes_grading with three attempts; a stale
or reviewed answer is never touched; the last failure marks it failed
- learning answers enqueue at once, tests at close; a grade
recalculates a finished attempt and fires AnswerGradedEvent after
commit
