InsightsSessionSubjectSource

How subject was decided: app (single-subject LTI application shortcut), xp (first XP earned in the session), activity (curriculum activity the parser recorded as AssignableEvent Completed), assessment (agreed Alpha Test line-item or assessment name), journal (vision journal classification), enrollment (the student's app-scoped course enrolment on the session date), or none (fallback Unknown). Null when subject is null.