Constant REQUEST_UNANSWERED 

pub const REQUEST_UNANSWERED: u64 = _; // 0u64

The application error code a request stream the peer opened is reset with when this endpoint abandons it: INTERNAL_ERROR, 0x0.

Dropping an inbound request is not the act REQUEST_CANCELLED describes. Draft-18 Section 3.3.2 grants a responder a cancel — “Receivers cancel requests if they are unable to or choose not to respond” — but a handle that fell out of scope chose nothing; it failed to serve, which is what StreamResetErrorCode::InternalError, “an implementation specific error” in Section 3.3.3, names. The two codes are on the wire, so a peer counting refusals can tell a deliberate rejection from a dropped request only if they differ.

It is also what a responder that already answered is reset with when it is dropped without finishing. A FIN there would claim the request completed, and for a subscription it has not: PUBLISH_DONE is still owed.