fix(htyws): preserve existing fields on course_group partial update

CourseGroup has treat_none_as_null=true, so partial updates would set
unsent fields to NULL. Merge with existing record before update to
preserve org_id, created_by, course_section_ids, and teachers.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

htyws/src/ws_all.rs

@@ -514,12 +514,28 @@ pub fn raw_update_course_group(
     let token = HtyToken::from_jwt(auth.clone().deref())?;
     let user_id = token.hty_id.ok_or_else(|| anyhow!("hty_id is required"))?;
 
+    let mut conn_holder = extract_conn(fetch_db_conn(&db_pool)?);
+    let conn = conn_holder.deref_mut();
+
+    // Load existing record to preserve fields not sent in the partial update
+    let existing = CourseGroup::find_by_id(
+        req_course_group.id.as_ref().unwrap(),
+        conn,
+    )?;
+
     let mut in_section_group = CourseGroup::from(&req_course_group)?;
+    // Merge: preserve existing values for fields not provided in the request
+    // (CourseGroup has treat_none_as_null=true, so None fields would be set to NULL)
+    if in_section_group.org_id.is_none() { in_section_group.org_id = existing.org_id; }
+    if in_section_group.created_by.is_none() { in_section_group.created_by = existing.created_by; }
+    if in_section_group.created_at.is_none() { in_section_group.created_at = existing.created_at; }
+    if in_section_group.course_section_ids.is_none() { in_section_group.course_section_ids = existing.course_section_ids; }
+    if in_section_group.teachers.is_none() { in_section_group.teachers = existing.teachers; }
     in_section_group.updated_by = Some(user_id);
 
     let res = CourseGroup::update(
         &in_section_group,
-        extract_conn(fetch_db_conn(&db_pool)?).deref_mut(),
+        conn,
     )?;
 
     Ok(res.id)