Raised when a node body raises asyncio.CancelledError itself.
asyncio.CancelledError is a BaseException and the pregel runner
treats cancelled task futures as silent tear-down (e.g. when it stops
sibling tasks after a peer fails). That is the correct behaviour for
framework-initiated cancellation, but a user node that raises
asyncio.CancelledError from its own body should surface as a node
failure, the same way any other exception would.
The retry layer converts user-raised asyncio.CancelledError into this
type so it flows through the normal error path and the run reports as
error instead of silently succeeding.
