cmux Backend

Use this skill for backend TypeScript, Cloud VM, provider, database, auth, rate-limit, retry, timeout, or telemetry work.

Core rules

Default backend TypeScript to Effect under web/app/api/**, web/services/**, and backend scripts that touch providers, databases, auth, rate limits, retries, timeouts, or telemetry.
Keep Next route handlers thin: parse the request, run one Effect program at the boundary, map typed errors to HTTP responses, and treat unexpected defects separately.
Use plain TypeScript only for trivial data shapes, constants, config files, frontend React code, or small glue where Effect would add ceremony without improving failure handling.
Cloud VM backend logic must stay in Vercel route handlers and Effect services backed by Postgres.
Do not reintroduce Rivet or a raw actor protocol for Cloud VM unless a later architecture doc explicitly changes the control plane.
Production and staging Cloud VM Postgres use the Vercel Marketplace AWS Aurora PostgreSQL OIDC/RDS IAM path.
Runtime env names are CMUX_DB_DRIVER=aws-rds-iam, AWS_ROLE_ARN, AWS_REGION, PGHOST, PGPORT, PGUSER, and PGDATABASE.
Run production/staging migrations with bun db:migrate:aws-rds-iam; never run Drizzle migrations from Vercel build or route startup.
Local development keeps using the CMUX_PORT-derived Docker Postgres path from bun dev.
Cloud VM create pricing gates should use Stack Auth team payment items when enabled.
Postgres remains the source of truth for VM lifecycle, active VM limits, idempotency, and usage events.