Rust SDK worker refusals

Workers answer a pushed request with PushClient::reply or refuse it with PushClient::refuse(correlation_id, code, words). PushWriter offers both methods on the same connection. A refusal accepts the closed codes busy, invalid, unavailable, and internal.

The wire-configured words limit is 1024 UTF-8 bytes, preserving a useful explanation while bounding storage and decoding. Both worker APIs validate the code and byte length before locking or writing the socket. Invalid data returns SdkError::Protocol with the bound or fault name and no application data.

Worker identities must fit in 993 UTF-8 bytes so a malformed refusal can name the full station within the same 1024-byte explanation bound. Registration rejects a longer identity with worker_station_too_long; names are never truncated.

let request = worker.recv()?;
if let liminal_sdk::PushReceiveOutcome::Frame(request) = request {
    worker.refuse(request.correlation_id(), "busy", "worker is busy")?;
}

A Rust conversation caller receives SdkError::WorkerRefused { code, words }. code is the worker code without the worker_ prefix, and words is exact. Display returns those words; Debug records only the code and the words' byte count. Route admission errors remain SdkError::Conversation. Classification uses the conversation's numeric reason code, never a prefix in its message.

The existing host-side server push awaiter returns the stable worker_<code> alone through its legacy PushReplyRefused error. Routed calls retain the validated refusal separately so its words reach only the authorised caller.

The wire fixture pins every code, a maximal UTF-8 words case, complete worker and caller frames, and an unchanged opaque reply. Its 0x0401–0x0404 conversation reasons map to worker_busy, worker_invalid, worker_unavailable, and worker_internal. The server logs malformed or reserved-flag replies by fault name without their bytes. A refusal settles its slot once; duplicate replies are discarded.

Verify the SDK's live TCP pin on a socket-capable host with cargo nextest run -p liminal-sdk --features embedded --lib refusal.