/**

* Top-level Fastify error handler that logs the full stack for any 5xx.

*

* Without this, 500 responses carry only Fastify's default 91-byte body and

* leave no trace in logs — production debugging has to infer the exception

* from the response body alone (see #309 investigation for why that's bad).

*

* 4xx errors carry their own statusCode and don't need stack logging — they

* are expected client errors with self-explanatory messages.

*/

export function registerErrorHandler(fastify) {

fastify.setErrorHandler(function (err, request, reply) {

const statusCode = err.statusCode ?? 500;

if (statusCode >= 500) {

request.log.error({

err,

method: request.method,

url: request.url,

hostname: request.hostname

}, 'Unhandled 5xx error');

}

reply.send(err);

});

}