Module validate 

Shared v1 frame-envelope validation (#376).

Client and broker validate the same four Frame envelope fields in the same order before touching a payload: envelope_version, kind, payload_protocol, payload_encoding. This module centralizes that check once; each call site keeps its own error type by mapping the neutral FrameValidationError onto its existing errors, so observable behavior (error variants, refusal codes, message strings) is unchanged.

The expected frame kind and payload protocol differ per call site (client expects RESPONSE frames, the broker Hello path expects REQUEST, the handoff relay expects EVENT), so both are explicit parameters rather than baked-in defaults.

Enums

FrameValidationError

Neutral envelope-validation failure.

Functions

validate_frame_envelope

Validate the four v1 envelope fields shared by every framed exchange.