Transport layer: bytes on and off the wire.
Owns protocol framing and, in a later slice, TLS termination behind the
CryptoProvider seam (docs/07) and pooled upstream connections (docs/04
§7). It knows nothing about routing decisions or tenancy semantics.
M1 implements the HTTP/1.1 cleartext ingress: [serve] accepts
connections, parses each request into an owned [IngressRequest] (with its
EndpointKind classified by [classify()]),
invokes an [IngressHandler], and writes the [IngressResponse]. The handler,
implemented by the binary, is where the request meets the engine pipeline.