chore: development environment setup + fix corrupted seed JSON

AGENTS.md

@@ -0,0 +1,49 @@
+# AGENTS.md
+
+## Cursor Cloud specific instructions
+
+### Services overview
+
+| Service | Port | Required | Notes |
+|---------|------|----------|-------|
+| MongoDB | 27017 | Yes | API cannot start without it |
+| Redis | 6379 | No | Graceful degradation; no token rotation in dev |
+| API (Fastify) | 4000 | Yes | `pnpm dev` from `apps/api/` |
+| Web (Vite) | 5173 | Yes | `pnpm dev` from `apps/web/` |
+
+### Starting MongoDB
+
+MongoDB 7 is installed system-wide. Since systemd is not available, start it manually:
+
+```bash
+mkdir -p /data/db
+mongod --dbpath /data/db --fork --logpath /var/log/mongodb.log --bind_ip_all
+```
+
+If forking fails (stale lock), remove `/data/db/mongod.lock` and `/tmp/mongodb-27017.sock` then retry.
+
+### Environment file
+
+Copy `.env.example` to `.env` at the repo root before starting the API. Default values work for local dev (no auth on MongoDB, Redis optional).
+
+### Build order gotcha
+
+The monorepo uses Turborepo with `composite` TypeScript projects. Stale `tsconfig.tsbuildinfo` files in `packages/` can cause spurious "Could not find declaration file" errors on typecheck/lint. The update script cleans these automatically, but if you hit this issue interactively, run:
+
+```bash
+find packages -name "tsconfig.tsbuildinfo" -delete && find packages apps -name "dist" -type d -exec rm -rf {} + 2>/dev/null; pnpm build
+```
+
+### Running standard commands
+
+See root `package.json` scripts. All are run via Turborepo:
+
+- `pnpm dev` — starts both API and web in watch mode
+- `pnpm typecheck` — type-checks all packages
+- `pnpm lint` — runs linting (TypeScript type-check for most packages)
+- `pnpm test` — runs Vitest unit/integration tests (uses `mongodb-memory-server`, no real DB needed)
+- `pnpm build` — full production build
+
+### Seed data note
+
+`modules/math-algebra/seeds/B1.json` had a corrupted JSON entry (literal control character). It has been patched. If you encounter similar JSON parse errors in seed files during `loadModules()`, check for malformed strings with unescaped control characters.

modules/math-algebra/seeds/B1.json

@@ -504,7 +504,14 @@
     "wrongChoiceReasons": {
       "B": "Check (4, 6): 4 + 6 = 10 ✓, but 6 = 2(4) + 1 = 9 ✗.",
       "C": "Check (6, 4): 6 + 4 = 10 ✓, but 4 = 2(6) + 1 = 13 ✗.",
-      "D": "Check (2, 5): 2 + 5 = 7 ✗ (not 10).[
+      "D": "Check (2, 5): 2 + 5 = 7 ✗ (not 10)."
+    },
+    "explanation": "Substitute y = 2x + 1 into x + y = 10: x + (2x + 1) = 10, so 3x + 1 = 10, x = 3, y = 7.",
+    "explanationSteps": ["Substitute y = 2x + 1 into x + y = 10.", "Simplify: 3x + 1 = 10.", "Solve: x = 3, y = 7."],
+    "hints": ["Replace y in the first equation using the second equation.", "Solve the resulting equation for x."],
+    "tags": ["systems", "substitution"],
+    "estimatedTimeSec": 50
+  },
   {
     "id": "ma-alg-b1-001",
     "moduleId": "math.algebra",