Whether the client has sent a notifications/cancelled for this request
(basic/utilities/cancellation). A long-running handler SHOULD poll this
and, when true, stop work and free resources promptly; the server
suppresses the late response for a cancelled request regardless. Always
false on transports that cannot deliver an out-of-band cancellation while
a request is in flight (e.g. the in-process / stdio NullContext).
Whether the client has sent a notifications/cancelled for this request (basic/utilities/cancellation). A long-running handler SHOULD poll this and, when true, stop work and free resources promptly; the server suppresses the late response for a cancelled request regardless. Always false on transports that cannot deliver an out-of-band cancellation while a request is in flight (e.g. the in-process / stdio NullContext).