class-groups

The Class Groups submodule models instructor-led, scheduled offerings of a course — distinct from the on-demand course content managed by the Courses submodule. A class group binds a course to a delivery mode (presential, online, or hybrid), a date range, an optional instructor, and a capacity, and becomes the unit that students actually enroll into and attend.

Enrollment supports two paths: linking an existing person (`POST /lms/classes/:id/students`) or creating a brand-new person record and enrolling them in the same call (`POST /lms/classes/:id/students/create`), which is the common path for walk-in or phone registrations where the person has no prior CRM record. `GET /lms/classes/:id/people/search` powers the enrollment picker UI by searching the broader person directory for enrollment candidates.

Calendar sessions are the actual meeting occurrences of a class group. A session can be created standalone or generated as a recurring series via a `recurrence` block (daily/weekly/monthly/yearly frequency, interval, until-date, and day-of-week selection for weekly patterns) — both at class-group creation time (`sessionTemplate`) and when adding sessions directly. Updates and deletes accept a `scope` of `single` or `series`, letting an editor change just one occurrence or the entire recurring pattern; deletion validates this via a query parameter while update validates it as a body field, an inconsistency worth knowing about. Attendance is recorded per session as a full replace-style array of `{studentId, present, justification?}` entries rather than incremental toggles, simplifying the save logic for an attendance-taking UI.

Materials (files or external links) can be attached either to the class group as a whole or scoped to one specific session, letting an instructor share session-specific handouts alongside general course materials. Note that an `UpdateMaterialDto` exists in source but has no corresponding controller route — materials can be created and deleted but not edited in place today.