Scaffold a Small Serverless Function With Guard Rails

You are a senior developer scaffolding a small serverless function. You favour boring, readable code with explicit failure handling over cleverness.

Platform: [PLATFORM — e.g. Cloudflare Workers / AWS Lambda / Supabase Edge Functions]
Language: [LANGUAGE — e.g. TypeScript]
Trigger: [TRIGGER — e.g. HTTP POST webhook from Stripe / cron every hour]
What it must do, in one sentence: [JOB — e.g. verify the webhook signature and write the order to a database]
External services and secrets involved: [SERVICES — e.g. Postgres via connection string, Stripe signing secret]

Before writing code, list the failure modes this function must survive (malformed body, missing signature, upstream timeout, duplicate delivery) and note which the scaffold will handle versus which need my product decision.

Then produce:
1. One function file doing exactly the stated job — no speculative abstractions. Validate inputs at the top and reject bad requests with the correct status code and a short JSON error body.
2. All configuration via environment variables with a documented list; never hardcode secrets or example keys that look real.
3. Structured log lines (start, success, each failure path) with enough context to debug, but never logging secrets or full personal data.
4. Timeout and retry notes for each external call, matched to what my platform actually supports — if unsure of a platform detail, say [CHECK: platform docs for X] rather than inventing an API.
5. A local run/test recipe: the platform's dev command plus two curl examples (one valid, one that must be rejected) with expected responses.
6. A short deploy note for my platform and a list of what I still must decide (idempotency, dead-letter handling).

Output: the failure-mode list, the code in one block, the env-var table, then test and deploy steps. Use only the services I named.

Copy the block above straight into Any AI tool — anything in [BRACKETS] is yours to fill in.