ROB-006: Cancellation is handled gracefully

Severity	Applies to	Spec section
error	both eras, stdio, http	2026-07-28/basic/patterns/cancellation#timing-considerations

On stdio, sends a request and cancels it at once with notifications/cancelled, then cancels a request that was never sent, then sends a cancellation without a requestId, then a new request. Both parties MUST handle cancellation races gracefully, invalid cancellations SHOULD be ignored, and a notification MUST NOT get a response (https://modelcontextprotocol.io/specification/2026-07-28/basic/index#notifications). A response to the cancelled request itself is allowed (it may have finished first). Fails if any cancellation is answered, or the next request is not. On Streamable HTTP, closing the response stream is the cancellation signal and MUST be treated as one (https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#cancellation): the client disconnects mid-request, and the next request must still be answered. Runs once per server.

From the command line: mcpprobe checks explain ROB-006. To leave it out of a run, add "ROB-006" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.