LearnSpace: full-stack educational whiteboard platform

Node.js/Express backend + vanilla JS frontend.
Features: real-time collaborative whiteboard (SSE), multi-page support,
LaTeX formulas, shapes/connectors, coordinate systems, number lines,
compass, zoom/pan, Catmull-Rom pencil smoothing, ruler/protractor with
rotation & resize controls, minimap navigation overlay, auto-measurements,
multi-page thumbnails sidebar, PNG export, page templates.
Student/teacher workflows: classes, assignments, library, dashboard.
Mobile responsive. SQLite (better-sqlite3).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/config.js

@@ -0,0 +1,65 @@
+'use strict';
+
+/* ── Environment configuration & startup validation ───────────────────────
+   Require this module BEFORE anything else that reads process.env.
+   Fails fast with a clear message if required vars are missing or weak.
+   ──────────────────────────────────────────────────────────────────────── */
+
+require('dotenv').config({ path: require('path').join(__dirname, '../.env') });
+
+const path   = require('path');
+const errors = [];
+
+function _require(key, { minLen, notValue } = {}) {
+  const val = process.env[key];
+  if (!val) { errors.push(`${key} is required`); return undefined; }
+  if (minLen   && val.length < minLen)  errors.push(`${key} must be at least ${minLen} chars (got ${val.length})`);
+  if (notValue && val === notValue)     errors.push(`${key} must not be the default placeholder value`);
+  return val;
+}
+
+function _optional(key, defaultVal = undefined) {
+  return process.env[key] || defaultVal;
+}
+
+/* ── Required vars ────────────────────────────────────────────────────── */
+const JWT_SECRET = _require('JWT_SECRET', {
+  minLen:   32,
+  notValue: 'change_this_to_a_long_random_string',
+});
+
+/* ── Optional vars with defaults ─────────────────────────────────────── */
+const NODE_ENV = _optional('NODE_ENV', 'development');
+if (!['development', 'production', 'test'].includes(NODE_ENV)) {
+  errors.push(`NODE_ENV must be development | production | test (got: "${NODE_ENV}")`);
+}
+
+const PORT_RAW = _optional('PORT', '3000');
+const PORT = Number(PORT_RAW);
+if (!Number.isInteger(PORT) || PORT < 1 || PORT > 65535) {
+  errors.push(`PORT must be an integer between 1 and 65535 (got: "${PORT_RAW}")`);
+}
+
+/* ── Fail fast ───────────────────────────────────────────────────────── */
+if (errors.length) {
+  process.stderr.write('\n[config] FATAL: invalid environment configuration:\n');
+  errors.forEach(e => process.stderr.write(`  ✗ ${e}\n`));
+  process.stderr.write('\nFix these issues in your .env file and restart.\n\n');
+  process.exit(1);
+}
+
+module.exports = Object.freeze({
+  /* env */
+  JWT_SECRET,
+  PORT,
+  NODE_ENV,
+  isProd:        NODE_ENV === 'production',
+  LOG_LEVEL:     _optional('LOG_LEVEL', NODE_ENV === 'production' ? 'info' : 'debug'),
+  CLIENT_ORIGIN: _optional('CLIENT_ORIGIN'),
+  /* paths */
+  DB_PATH:       _optional('DB_PATH',     path.join(__dirname, '../data/learnspace.db')),
+  UPLOADS_DIR:   _optional('UPLOADS_DIR', path.join(__dirname, '../uploads')),
+  /* constants */
+  BCRYPT_ROUNDS: 12,
+  MAX_FILE_SIZE: 50 * 1024 * 1024,
+});