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+# classroomController.js split plan
+
+**Source:** `backend/src/controllers/classroomController.js` — 1618 lines, 70 functions  
+**Target:** `backend/src/controllers/classroom/` — 8 files  
+**Strategy:** pure mechanical split, no behaviour changes, facade preserves compatibility
+
+---
+
+## Target structure
+
+```
+backend/src/controllers/
+  classroomController.js          ← 8-line re-export facade (unchanged public API)
+  classroom/
+    _shared.js                    ← shared helpers used by multiple files
+    sessions.js                   ← session lifecycle + guest tokens
+    strokes.js                    ← whiteboard strokes + cursor preview
+    pages.js                      ← page CRUD + templates + board theme
+    chat.js                       ← chat messages, reactions, attachments, export
+    permissions.js                ← draw permissions, hand-raise, mute, screen, attendance
+    sim.js                        ← simulation relay (simOpen/State/Mode/Annotate/Close)
+    admin.js                      ← history, notes, templates, admin views
+```
+
+---
+
+## File mapping
+
+### `classroom/_shared.js`
+Helpers used by 2+ files. Exports: `{ GUEST_EVENTS, emitToSession, hasAccess, canDraw }`
+
+| Symbol | Lines | Used by |
+|--------|-------|---------|
+| `GUEST_EVENTS` | 21–27 | sessions, strokes, pages, permissions, sim |
+| `emitToSession` | 31–34 | sessions, strokes, pages, chat, permissions, sim |
+| `hasAccess` | 37–48 | sessions, strokes, pages, chat, permissions, admin |
+| `canDraw` | 13–18 | strokes |
+
+Imports: `db`, `broadcastToSession` from `ws-server`
+
+---
+
+### `classroom/sessions.js`
+Session lifecycle, signal (WebRTC), guest tokens.
+
+| Function | Lines |
+|----------|-------|
+| `createSession` | 51–105 |
+| `getSession` | 106–128 |
+| `endSession` | 129–145 |
+| `getActiveSession` | 146–163 |
+| `getMyActive` | 164–177 |
+| `joinSession` | 178–210 |
+| `leaveSession` | 211–231 |
+| `getMySession` | 385–433 |
+| `signal` | 359–384 |
+| `generateGuestToken` | 1520–1531 |
+| `revokeGuestToken` | 1532–1542 |
+| `getGuestToken` | 1543–end |
+
+Imports: `db`, `crypto`, `invalidateSession`, `emitToUser` (from `ws-server`), `_shared`
+
+---
+
+### `classroom/strokes.js`
+Whiteboard stroke CRUD + live cursor/preview broadcast.
+
+| Function | Lines |
+|----------|-------|
+| `postStrokes` | 568–608 |
+| `getStrokes` | 609–635 |
+| `updateStroke` | 636–662 |
+| `deleteStroke` | 663–686 |
+| `clearPage` | 687–700 |
+| `previewStroke` | 815–840 |
+| `broadcastCursor` | 901–918 |
+
+Imports: `db`, `_shared`
+
+---
+
+### `classroom/pages.js`
+Page CRUD, templates, board theme.
+
+| Function | Lines |
+|----------|-------|
+| `getPages` | 701–723 |
+| `addPage` | 449–472 |
+| `changePage` | 473–488 |
+| `updatePageTemplate` | 489–503 |
+| `updateBoardTheme` | 504–518 |
+| `renamePage` | 724–740 |
+| `duplicatePage` | 741–769 |
+| `deletePage` | 770–799 |
+
+Imports: `db`, `_shared`
+
+---
+
+### `classroom/chat.js`
+Chat messages, reactions, file attachments, export, CHAT_UPLOADS_DIR setup.
+
+| Symbol | Lines |
+|--------|-------|
+| `CHAT_UPLOADS_DIR` | 9–10 |
+| `ALLOWED_REACTIONS` | 1027 |
+| `sendChat` | 232–268 |
+| `getChat` | 269–320 |
+| `pinMessage` | 841–864 |
+| `reactToMessage` | 1028–1074 |
+| `uploadChatAttachment` | 1019–1026 |
+| `exportChat` | 1244–1275 |
+
+Imports: `db`, `path`, `fs`, `crypto`, `emitToUser` (from `ws-server`), `_shared`
+
+---
+
+### `classroom/permissions.js`
+Draw permits, hand-raise, mute, screen share, online students.
+
+| Function | Lines |
+|----------|-------|
+| `getParticipants` | 321–340 |
+| `getAttendance` | 341–358 |
+| `getOnlineStudents` | 434–448 |
+| `raiseHand` | 519–537 |
+| `lowerHand` | 538–550 |
+| `getHands` | 551–567 |
+| `allowDraw` | 865–882 |
+| `revokeDraw` | 883–900 |
+| `mutePeer` | 800–814 |
+| `screenStart` | 919–930 |
+| `screenStop` | 931–941 |
+
+Imports: `db`, `emitToUser`, `invalidateDrawCache` (from `ws-server`), `getOnlineUserIds` (from `sse`), `_shared`
+
+---
+
+### `classroom/sim.js`
+Simulation relay — teacher broadcasts sim events to students.
+
+| Function | Lines |
+|----------|-------|
+| `simOpen` | 945–958 |
+| `simState` | 961–976 |
+| `simMode` | 979–991 |
+| `simAnnotate` | 994–1004 |
+| `simClose` | 1007–1018 |
+
+Imports: `db`, `_shared`
+
+---
+
+### `classroom/admin.js`
+History, notes, board templates, admin dashboards.
+
+| Function | Lines |
+|----------|-------|
+| `getNotes` | 1075–1082 |
+| `saveNotes` | 1083–1097 |
+| `getClassHistory` | 1098–1140 |
+| `getMyHistory` | 1141–1188 |
+| `getSessionSummary` | 1189–1243 |
+| `getAllNotes` | 1276–1294 |
+| `deleteHistorySession` | 1295–1320 |
+| `adminGetActiveSessions` | 1321–1341 |
+| `adminGetAllSessions` | 1342–1422 |
+| `adminGetTeachersList` | 1423–1434 |
+| `getTemplates` | 1435–1441 |
+| `saveTemplate` | 1442–1473 |
+| `deleteTemplate` | 1474–1479 |
+| `loadTemplate` | 1480–1519 |
+
+Imports: `db`, `_shared`
+
+---
+
+## Facade (`classroomController.js` after split)
+
+```js
+module.exports = {
+  ...require('./classroom/sessions'),
+  ...require('./classroom/strokes'),
+  ...require('./classroom/pages'),
+  ...require('./classroom/chat'),
+  ...require('./classroom/permissions'),
+  ...require('./classroom/sim'),
+  ...require('./classroom/admin'),
+};
+```
+
+`routes/classroom.js` imports from `'../controllers/classroomController'` — unchanged.
+
+---
+
+## What does NOT change
+- All function names — unchanged
+- All route bindings in `routes/classroom.js` — unchanged  
+- All public exports from `classroomController.js` — same set
+- DB queries — moved verbatim, not rewritten
+- Error responses — unchanged
+
+## Risks
+- `simClose` (line 1007) references `emitToSession` — must be imported from `_shared`
+- `sendChat` builds URLs with `req.protocol + '://' + req.get('host')` — needs no extra imports
+- `getSessionSummary` (line 1189) is 54 lines — complex, move carefully