Validate a CircleCI pipeline config by compiling it — the equivalent of the
`circleci config validate` CLI command. Pass the raw config YAML (the contents of
.circleci/config.yml) as config; the server expands orbs, resolves parameter expressions,
and expands matrix jobs, returning valid=true on success or valid=false with the
compilation errors on failure. Supply org (a slug like "gh/acme" or a
UUID) whenever the config references anything org-scoped: private registry orbs, or URL
orbs — any orb whose value is a URL rather than "namespace/name@version", which are gated
by the org's URL orb allow-list. Without org, only public registry orbs resolve, so those
references fail with errors like "not permitted by the organization's URL orb allow-list"
or "orb not found" — these are false negatives from missing org context, NOT real config
problems, so before reporting a config invalid, check whether it declares private or URL
orbs and if so retry with org. set preview_next=true to preview upcoming,
potentially breaking config changes; pass pipeline_parameters to resolve
<< pipeline.parameters.* >> expressions.