Function wrapRawChannelMessage

Wraps an arbitrary (non-LXMF) payload into a rfed channel SEND payload.

Like wrapChannelMessage but skips LXMF serialisation entirely. The plaintext is just the RTID prelude (magic + sender public key) followed by the raw payload bytes — the application payload is self-describing and self-authenticating (e.g. a Dacar delta carries its own issuer hash, Ed25519 signature, and timestamp), so the LXMF destination/source/signature framing is redundant and only wastes MTU.

Wire format (RFed/SPEC.md "CANONICAL WIRE FORMAT"; the inner_blob is opaque to the node):

plaintext   = "RTID"(4) ‖ sender_identity_pub(64) ‖ payload
inner_blob  = EC_encrypt(channel_identity.X25519_pub, plaintext)
rfed_payload= channel_hash(16) ‖ inner_blob ‖ stamp(32)?
Copy

The RTID prelude is retained so the message is identifiable as a rfed channel message and the sender identity is recoverable by subscribers. The node treats inner_blob opaquely — it never decrypts or inspects it — so this is fully compatible with both the Rust and JS rfed nodes. Only subscribers holding the channel private key can recover the payload.

Integrity is the application's responsibility: the channel EC gate ensures only authorised subscribers can produce a valid inner_blob, but the payload itself should carry its own authentication (e.g. an embedded Ed25519 signature) since rfed does not verify it.