Validate the draft Streamable HTTP request headers against the JSON-RPC body.
Returns a HeaderMismatch (-32001) exception on failure, or null when the
request is valid — or when the request is not a draft request (older versions
did not define these headers, so they are not enforced).
isDraft is the effective draft signal for the request (header OR body
_meta.protocolVersion), matching how the rest of the POST handler classifies
the request: the draft protocol is stateless-only and may negotiate via the
body alone, so a body-only-draft request still has its draft headers enforced.
Validate the draft Streamable HTTP request headers against the JSON-RPC body. Returns a HeaderMismatch (-32001) exception on failure, or null when the request is valid — or when the request is not a draft request (older versions did not define these headers, so they are not enforced).
isDraft is the effective draft signal for the request (header OR body _meta.protocolVersion), matching how the rest of the POST handler classifies the request: the draft protocol is stateless-only and may negotiate via the body alone, so a body-only-draft request still has its draft headers enforced.