billing skeleton: bun + hono + sqlite, seed + happy path

README.md

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+# monk-code-screen
+
+Billing/subscriptions/invoicing backend skeleton. Bun + Hono + `bun:sqlite` (zero network deps at runtime; TS runs natively, no build step).
+
+## ⚡ START COMMAND (sticky)
+
+```sh
+bun run dev          # http://localhost:3000, hot reload
+```
+
+Other commands:
+
+```sh
+bun run start        # no watch
+bun run db:reset     # wipe data.db and reseed
+bunx tsc --noEmit    # typecheck
+```
+
+## Layout
+
+```
+src/index.ts    Hono app + routes
+src/db.ts       opens data.db, applies schema, seeds if empty (runs on import)
+src/schema.sql  customers / plans / subscriptions / invoices (idempotent)
+```
+
+DB is `data.db` at repo root (WAL, FK on). Boot always re-applies schema, so adding a table = edit schema.sql + restart.
+
+## Routes
+
+```sh
+curl localhost:3000/health
+curl localhost:3000/customers
+curl localhost:3000/customers/cus_ada/invoices
+curl -X POST localhost:3000/subscriptions \
+  -H 'content-type: application/json' \
+  -d '{"customer_id":"cus_grace","plan_id":"plan_basic"}'
+```
+
+`POST /subscriptions` is the happy path: validates with zod, creates subscription + first invoice in one transaction, returns both (201).
+
+## Seed data
+
+- customers: `cus_ada`, `cus_grace`
+- plans: `plan_basic` ($10/mo), `plan_pro` ($50/mo)
+- `cus_ada` has an active `sub_1` on pro with open `inv_1`
+
+## Extension cheatsheet (interview)
+
+- New route: add to `src/index.ts`, `db.query(...).all()/get()`, `db.run(sql, [params])`
+- Multi-write: `db.transaction(() => { ... })()`
+- Validation: `z.object({...}).safeParse(await c.req.json())`
+- New table: append `CREATE TABLE IF NOT EXISTS` to schema.sql, restart (or `db:reset` if changing existing tables)