The wire contract between the CoreBluetooth interposer and the host helper: CBOR
messages with a 4-byte length prefix. SPEC.md is the prose source of truth,
protocol.cddl the machine-checkable schema, VERSION the single protocol
version.
One spec, two codecs: Swift (swift/) for the helper, C (c/) for the
interposer, kept in agreement by emitting canonical CBOR and proven against each
other by the byte-parity vectors in both test suites. The wire carries three
frame kinds, told apart by the op in key 0: requests (guest to host, with the
capability token), responses (host to guest, with a status), and events (host to
guest, unsolicited, op in the 128-and-up range). It moves GATT operations and
byte payloads only; no key material crosses it.