[cpp-RCP-08] E2E CRC failure reported as "CRC_ERROR", never mapped to the spec's numeric POCI_FAILURE(12) code #76

Location: include/rcp/e2e.hpp — E2eErrc::crc_error and its category message (~lines 74-96, 244-249).

Finding: A CRC mismatch is surfaced internally as E2eErrc::crc_error, which renders as the string "CRC_ERROR". The governing specification's numeric error-code table has no CRC_ERROR entry; the code it actually assigns to "CRC of request does not match" is POCI_FAILURE (value 12). There is currently no mapping anywhere in this codebase from the internal E2eErrc enum to that numeric spec error code, so when a safety-relevant request fails its E2E CRC check, the failure can't currently be reported back over the wire using the spec-defined numeric code a conformant peer would recognize.

Recommendation: Add a mapping from E2eErrc::crc_error to the numeric error code 12 (POCI_FAILURE) for use wherever error responses are built on the wire, and keep "CRC_ERROR" as internal-only prose/logging rather than a wire-visible identifier.

Verification: Independently re-read include/rcp/e2e.hpp against current HEAD (commit 4b9449a, 2026-07-29) and cross-checked the numeric error-code table in the governing specification's error-handling section. Confirmed there is no CRC_ERROR entry in that table and that the CRC-mismatch code is value 12; confirmed no mapping from E2eErrc to that numeric value exists anywhere in the codebase (grep for the value/name found nothing).

Filed from the 2026-07-29 ecosystem audit register; independently re-verified against current HEAD before filing.