Validation errors

code: validation_error is returned with 400 Bad Request for any malformed payload — missing required fields, invalid enum values, out-of-range integers, type mismatches, or invalid JSON.

The details object carries structured context. The most common shape is:

{
  "error": "title is required",
  "code": "validation_error",
  "request_id": "8a1f2c4e-9b6d-4a17-8f3a-21e4c0a1b2d3",
  "details": { "field": "title" }
}

Do not retry the same payload — fix the request first.