Data signed successfully (stream).

Malformed multipart, invalid data, or key does not support the requested operation. PQC session transport is also refused here: an X-PQC-Transport: true or X-PQC-Session header on this route yields .../errors/pqc-transport-not-available-for-streaming, refused before any body byte is read.

Unauthorized.

kid not found or unsuitable.

Request Timeout: the request body was not fully received within the deployment's configured total-duration budget for one streaming upload (crypto.stream.max-read-duration-ms). The detail names that budget in milliseconds. Emittable only while the small part is still being read: once the response is committed no status is representable at all and the stream is truncated instead, per the PRD §141 fail-closed contract. The connection is closed (Connection: close) on this response, so a refused upload cannot keep streaming its body into a drain (RFC 9110 §15.5.9).

Conflict: the tenant's key-protection backend is not configured - never declared, or declared but not yet bound. Durable: complete the setup rather than retrying. No Retry-After is sent.

Payload Too Large: the small part (metadata or header) exceeded its 2 MiB cap. file has NO size limit — this response never refers to the payload.

Too Many Requests: the streaming concurrency bound is full, either globally or for this tenant. Retry-After carries the suggested delay in seconds. This bound replaced the edge client_max_body_size ceiling PRD §130 removed, so it is emittable on every streaming endpoint.

Unexpected failure during streaming signing.

Service Unavailable: the tenant's key-protection backend is bound but not currently usable. Transient - retry after the Retry-After interval. The body is oracle-safe and names no backend, token, slot, PIN or vendor.