Discussion only open while a study is active; v2.11.1

- Community posts, replies, likes and lesson comments are refused (403) for finished and planned studies
- Reading a closed study's community/comments returns an empty list with closed:true
- Discussion hub lists only active studies; community page shows a closed notice
- Lesson page hides Lesson Discussion, 'Discuss this lesson' and 'Go to Community' for inactive studies; Community buttons hidden on study/dashboard pages
- Tests for isStudyDiscussionOpen

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/study-helpers.js

@@ -225,6 +225,18 @@ export async function backfillCompletedStudies() {
   return updated
 }
 
+// Discussion (community posts, replies, likes and lesson comments) is only open while a
+// study is active. Finished and planned studies are closed.
+export function isStudyDiscussionOpen(studySlug) {
+  const normalized = normalizeStudySlug(studySlug)
+  const studies = state.cachedSiteContent?.studies
+  if (!normalized || !Array.isArray(studies)) return false
+  const study = studies.find(item => normalizeStudySlug(item?.slug) === normalized)
+  return Boolean(study) && getEffectiveStudyStatus(study) === 'active'
+}
+
+export const DISCUSSION_CLOSED_MESSAGE = 'Discussion is only open while a study is active.'
+
 export function findStudyUserById(userId) {
   if (typeof userId !== 'string' || !userId.trim()) return undefined
   return state.studyUsers.find(user => user.id === userId)