Constant RPC_STREAM_ERROR_TAG 

pub const RPC_STREAM_ERROR_TAG: u64 = 48900; // 48_900u64

CBOR tag number reserved for the mid-stream error sentinel described in docs/design/rpc-transport.md §3.3: when a genuinely incremental application/cbor-seq sequence response (a @stream procedure, see cratestack#282/#283) fails partway through, the last item of the sequence is Tag(RPC_STREAM_ERROR_TAG, RpcErrorBody-as-CBOR-map) — CBOR major type 6, this tag number, wrapping RpcErrorBody encoded as a plain CBOR map — in place of what would otherwise be the next unwrapped out item. No further items follow it; end of body comes immediately after.

Not IANA-registered. Picked from the CBOR tags registry’s “First Come First Served” range (32768–18446744073709551615; https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml) and confirmed unassigned as of 2026-08-02 — see cratestack#281 for the verification method and the collision-risk flag for a pre-merge human double-check.