Groq 401: verify the key starts with gsk_ and test it against /models

[groq-common-errors skill]: confirm the key starts with gsk_: check the first four characters of the environment value. Then test the key directly with curl against https://api.groq.com/openai/v1/models with the Authorization Bearer header: it should return 200. If it does not, the key is invalid, expired, or revoked: generate a new one in the console. Never paste the full key into logs or chat while debugging.

Context: A 401 on Groq is almost always the key, not the request.