discussions

These two controllers sit side-by-side under `/lms/course-lessons/:lessonId/` and look superficially similar — both require the caller to be enrolled in the lesson's course (via a shared `assertStudentAccess` check that resolves `person_id` from the authenticated user and verifies a non-cancelled `course_enrollment`), and both anchor entries to a `playerTimeSeconds` position in the lesson video. The key behavioral difference is visibility: discussion topics are shared across every enrolled student in the lesson — `GET /discussion/topics` returns the full thread tree with no per-user filtering, only computing a `likedByMe` flag per topic for the viewer — while notes are strictly private, with every query filtered to `person_id = caller`. A student cannot see another student's notes under any circumstance.

Discussion replies are not a separate entity; a reply is just another topic row with `parentTopicId` set, and the tree is reconstructed in memory on each read. Likes use a composite-unique `(topic_id, person_id)` row with `ON CONFLICT DO NOTHING` on like and an unconditional delete on unlike, so liking twice or unliking when not liked are both silent no-ops rather than errors. Posted content is run through a manual regex-based sanitizer that strips `<script>`/`<style>` blocks, inline `on*` event attributes, and `javascript:` URIs — it is not a full HTML sanitizer library, so other tags/attributes pass through untouched.