Completed studies: finishing a study keeps access after leaving; certificates always shown; no reminders for finished studies; v2.11.0

- Completion is stored on the user (completedStudySlugs, sticky) when every lesson is done; backfilled at startup
- Lessons, notes, progress, quiz, community and certificate stay open for completed studies after leaving the enrollment
- Dashboard/My Account list completed studies with Review Lessons and certificate access
- Study page shows a completed banner
- Lesson-release reminders, weekly digest and re-engagement emails skip finished studies
- Fix: streak fields (current/longest/last studied) and firstCompletionAt were dropped on every restart when users were loaded
- Tests for completion/access/re-engagement

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

server/study-helpers.js

@@ -22,7 +22,7 @@ import {
   DOWNLOAD_TOKEN_TTL_MS,
 } from './config.js'
 import { state } from './state.js'
-import { queueStudyRemindersWrite, queueStudyUsersWrite, queueStudySessionsWrite } from './data.js'
+import { queueStudyRemindersWrite, queueStudyUsersWrite, queueStudySessionsWrite, loadUserProgress } from './data.js'
 
 // ── Username / slug normalizers ────────────────────────────────────────────
 
@@ -163,6 +163,68 @@ export function isStudyUserEnrolled(user, studySlug) {
   return Array.isArray(user.enrolledStudySlugs) && user.enrolledStudySlugs.includes(normalized)
 }
 
+// A student who has finished every lesson in a study keeps access to it (lessons, notes,
+// certificate) even if they later leave the enrollment. Completion is stored on the user
+// so it survives content edits and un-enrolling.
+export function isStudyUserCompleted(user, studySlug) {
+  const normalized = normalizeStudySlug(studySlug)
+  if (!normalized || !user) return false
+  return Array.isArray(user.completedStudySlugs) && user.completedStudySlugs.includes(normalized)
+}
+
+export function hasStudyAccess(user, studySlug) {
+  return isStudyUserEnrolled(user, studySlug) || isStudyUserCompleted(user, studySlug)
+}
+
+// Enrolled studies plus finished ones, deduplicated. Sent to the client as the list of
+// studies the student can open.
+export function getAccessibleStudySlugs(user) {
+  const enrolled = Array.isArray(user?.enrolledStudySlugs) ? user.enrolledStudySlugs : []
+  const completed = Array.isArray(user?.completedStudySlugs) ? user.completedStudySlugs : []
+  return [...new Set([...enrolled, ...completed])]
+}
+
+// Every lesson (released or not) is required, matching the certificate rules.
+export function getRequiredSectionIds(studySlug) {
+  const content = state.cachedSiteContent
+  if (!content || !Array.isArray(content.studies)) return null
+  const study = content.studies.find(item => item?.slug === studySlug)
+  if (!study || !Array.isArray(study.sections)) return null
+  return study.sections.filter(item => item?.id).map(item => item.id)
+}
+
+// Marks the study completed on the user when every required lesson is done. Sticky: never
+// removed, so a later new lesson doesn't revoke access. Returns true if newly completed.
+export function markStudyCompletedIfDone(user, studySlug, completedSectionIds) {
+  const normalized = normalizeStudySlug(studySlug)
+  if (!normalized || isStudyUserCompleted(user, normalized)) return false
+  const required = getRequiredSectionIds(normalized)
+  if (!required || required.length === 0) return false
+  if (!required.every(id => completedSectionIds.includes(id))) return false
+  user.completedStudySlugs = [...(Array.isArray(user.completedStudySlugs) ? user.completedStudySlugs : []), normalized]
+  user.updatedAt = new Date().toISOString()
+  queueStudyUsersWrite()
+  return true
+}
+
+// One-off pass at startup so students who finished a study before this existed get the flag.
+export async function backfillCompletedStudies() {
+  if (!state.cachedSiteContent) return 0
+  let updated = 0
+  for (const user of state.studyUsers) {
+    const progress = await loadUserProgress(user.id)
+    // Enrolled studies plus any with saved progress, so students who already left are caught too
+    const slugs = new Set([
+      ...(Array.isArray(user.enrolledStudySlugs) ? user.enrolledStudySlugs : []),
+      ...Object.keys(progress.byStudy ?? {}),
+    ])
+    for (const slug of slugs) {
+      if (markStudyCompletedIfDone(user, slug, progress.byStudy[slug]?.completedSectionIds ?? [])) updated++
+    }
+  }
+  return updated
+}
+
 export function findStudyUserById(userId) {
   if (typeof userId !== 'string' || !userId.trim()) return undefined
   return state.studyUsers.find(user => user.id === userId)
@@ -649,6 +711,7 @@ export async function scheduleStudyReminders(sendStudyReminderEmail) {
 
     const userSent = state.studyReminders.users[user.id] ?? {}
     for (const studySlug of enrolledStudySlugs) {
+      if (isStudyUserCompleted(user, studySlug)) continue // finished studies don't need lesson reminders
       const study = Array.isArray(state.cachedSiteContent.studies)
         ? state.cachedSiteContent.studies.find(item => normalizeStudySlug(item?.slug) === studySlug)
         : undefined
@@ -724,7 +787,9 @@ export async function scheduleReengagementEmails(sendStudyReengagementEmail) {
 
     const enrolledStudySlugs = Array.isArray(user.enrolledStudySlugs) ? user.enrolledStudySlugs : []
     const studies = Array.isArray(state.cachedSiteContent.studies) ? state.cachedSiteContent.studies : []
+    // Studies the student already finished aren't "unfinished business" for a come-back nudge.
     const enrolledStudies = enrolledStudySlugs
+      .filter(slug => !isStudyUserCompleted(user, slug))
       .map(slug => studies.find(s => normalizeStudySlug(s?.slug) === slug))
       .filter(Boolean)
 
@@ -782,6 +847,7 @@ export async function scheduleWeeklyDigestEmails(sendStudyWeeklyDigestEmail) {
     const newlySentByStudy = {}
 
     for (const studySlug of enrolledStudySlugs) {
+      if (isStudyUserCompleted(user, studySlug)) continue
       const study = Array.isArray(state.cachedSiteContent.studies)
         ? state.cachedSiteContent.studies.find(item => normalizeStudySlug(item?.slug) === studySlug)
         : undefined