The full 1.0 client surface, matching the protocol v2 wire definitions from donglora-protocol 1.0.0.
* Public API is now async. The blocking Client<T: Transport> is replaced by Dongle (from donglora_client::connect / connect_with / ConnectOptions).
* src/client.rs and src/codec.rs are removed in favor of src/dongle.rs (high-level surface), src/session.rs (per-client tag/slot state), src/retry.rs (RetryPolicy + tx_with_retry), src/errors.rs (thiserror-based ClientError / ClientResult). src/protocol.rs is replaced by direct donglora-protocol imports.
* Transport is now tokio-serial for USB and tokio::net::{UnixStream, TcpStream} for mux, replacing the blocking serial + shim model.
* Dongle::tx_with_retry(data, &RetryPolicy) implements PROTOCOL.md §6.10 randomized backoff for CHANNEL_BUSY / EBUSY, returning a TxOutcome with per-attempt trace.
* Background keepalive task pings every 500 ms on host idle, tracking the 1 s inactivity timeout from §3.4 with 2x margin. Disable via ConnectOptions::keepalive(false).
* Auto-recovery from ERR(ENOTCONFIGURED): the Dongle caches the last SET_CONFIG and silently re-applies on session drop, retrying once.
* Error taxonomy switches from anyhow to thiserror. Transport-level conditions (Timeout, TransportClosed, ReaderExited, BadFrame) are first-class.
* Examples rewritten for the async API: examples/ping.rs, examples/tx.rs, examples/rx.rs all target the MeshCore US preset (910.525 MHz / BW 62.5 / SF 7 / CR 4/5 / sync 0x1424 / 20 dBm). examples/common/mod.rs holds the shared helper.
* tests/vectors.rs gains protocol-level roundtrip coverage anchored to the published donglora-protocol 1.0.0 types.
swaits
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