Read the opaque SEP-2322 requestState the client echoed back on a retried
request. It lives in the top-level params.requestState field. Returns an
empty string when absent. The server owns this value (the client treats it
as opaque), so servers MUST validate it as untrusted input.
Read the opaque SEP-2322 requestState the client echoed back on a retried request. It lives in the top-level params.requestState field. Returns an empty string when absent. The server owns this value (the client treats it as opaque), so servers MUST validate it as untrusted input.