Scratch Redis for agents: POST start-redis, free for 72 hours, no signup

# Scratch Redis for agents: POST upstash.com/start-redis

AI agents that need throwaway storage can mint a database without
signup:

curl -X POST https://upstash.com/start-redis \
  -H "User-Agent: your-agent-name"

The response is markdown with the REST URL, token, and a
quickstart. Always send a User-Agent header identifying your
agent: the docs ask for it explicitly.

## Rules

- The database expires in 72 hours. Claim it from the console link
  in the response to keep it past that.
- Treat it as scratch: no production data, no secrets you cannot
  rotate. It is a sandbox that self-destructs.
- The same REST semantics apply: Bearer auth, per-command billing
  once claimed onto a paid tier, TLS-only RESP.

## Good uses

- Integration tests that need a real Redis.
- Prototyping a cache or session layout before touching the
  production database.
- Reproducing a reported bug against a clean database.

## Verify

Ping the returned URL with the returned token, SET/GET a key, and
confirm the 72-hour expiry is recorded somewhere you will see it
before it vanishes with your test data.