Every route was registered for GET only, so HEAD answered 405, and on
the JSON routes that 405 said "Internal server error". chi's GetHead
now serves HEAD with the GET handler; /ip and /ip/ register HEAD
themselves, as GetHead does not reach them. The /api/v1 and /ip route
groups answer a path they lack with a JSON 404 "Not found", and the
other methods the router knows (POST, PUT, PATCH, DELETE, OPTIONS,
TRACE, CONNECT) with a JSON 405 "Method not allowed" whose Allow header
names GET and HEAD. JSONValidationMiddleware gives a 4xx sent without a
JSON body the status's standard text instead of "Internal server error".
Model: opus-5-5