feat!: migrate firmware to DongLoRa Protocol v2 wire format

Wire-incompatible break with the 0.x protocol. Every host-side path (UART, USB CDC, framing, radio dispatcher, display update channel) speaks the v2 wire format defined in PROTOCOL.md.

* Replace the host framing path with streaming FrameDecoder + encode_frame from donglora-protocol, matching the new (type_id, tag, payload) shape.

* Update src/channel.rs and src/host/{uart,usb,framing}.rs for the new frame semantics: per-request tag echo, CRC checked in the decoder, async ERR fan-out on tag 0.

* Rework src/radio.rs to emit RX / TX_DONE / OK / ERR messages in v2 shape, including RxOrigin, TxDonePayload, and SetConfigResult codes.

* Update src/protocol.rs glue to re-export v2 types from donglora-protocol and drop the legacy 0.x shim surface.

* Refresh PROTOCOL.md to the v2 normative spec (kept in sync with the donglora-protocol crate).

* Minor display and main-loop cleanups needed for the new radio event shape.

src/channel.rs

@@ -1,54 +1,84 @@
-//! Inter-task communication channels.
+//! Inter-task communication channels for DongLoRa Protocol v2.
 //!
-//! - [`CommandChannel`]: USB → Radio (host commands)
-//! - [`ResponseChannel`]: Radio → USB (firmware responses)
-//! - [`DisplayCommandChannel`]: USB → Display (on/off/reset)
-//! - [`RadioEventChannel`]: Radio → Display (typed events from the radio)
+//! - [`CommandChannel`]: host_task → radio_task (tag-correlated commands)
+//! - [`OutboundChannel`]: radio_task → host_task (tag-correlated OK/ERR/TX_DONE
+//!   and tag-0 async RX/ERR events in one queue)
+//! - [`DisplayCommandChannel`]: host_task → display_task (internal only —
+//!   `On` on connect, `Reset` on disconnect; no longer driven from the wire)
+//! - [`RadioEventChannel`]: radio_task → display_task (typed mode/packet events)
 
 use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
 use embassy_sync::channel::Channel;
 
-use crate::protocol::{Command, RadioConfig, Response};
+use crate::protocol::{Command, DeviceMessage, LoRaConfig};
 
-/// Display commands routed from host_task to display_task.
-#[derive(Debug, Clone, Copy, defmt::Format)]
-pub enum DisplayCommand {
-    On,
-    Off,
-    #[allow(dead_code)] // only used by USB host task, not UART
+// ── Host → Radio: tag-correlated commands ───────────────────────────
+
+/// An event flowing from the host task into the radio task.
+///
+/// `Command` carries a non-zero correlation tag (the host framing layer
+/// rejects tag=0 before it reaches here). `Reset` is a lifecycle signal
+/// from the host transport layer (DTR drop, UART teardown, or spec §3.4
+/// inactivity timeout) telling the radio to park back to Unconfigured
+/// and drain queues silently.
+#[allow(clippy::large_enum_variant)]
+#[derive(Debug, Clone)]
+pub enum InboundEvent {
+    Command { tag: u16, cmd: Command },
     Reset,
 }
 
-/// USB-to-display command channel (depth 4: display commands are rare events).
-pub type DisplayCommandChannel = Channel<CriticalSectionRawMutex, DisplayCommand, 4>;
+/// Host-to-radio event channel (depth 8).
+pub type CommandChannel = Channel<CriticalSectionRawMutex, InboundEvent, 8>;
 
-/// Host-to-radio command channel (depth 16: buffer bursty host command sequences).
-pub type CommandChannel = Channel<CriticalSectionRawMutex, Command, 16>;
+// ── Radio → Host: OK / ERR / TX_DONE / RX / async ERR ──────────────
 
-/// Radio-to-host response channel (depth 32: buffer RX packets while USB writes).
-pub type ResponseChannel = Channel<CriticalSectionRawMutex, Response, 32>;
+/// One outbound D→H frame carrying its tag. Tag-correlated messages
+/// (OK, ERR in response, TX_DONE) carry the originating command's tag;
+/// async events (RX, async ERR) carry `tag = 0x0000`.
+#[derive(Debug, Clone)]
+pub struct OutboundFrame {
+    pub tag: u16,
+    pub msg: DeviceMessage,
+}
 
-/// Radio → downstream typed events. The radio task emits one of these at
-/// every mode transition and every RF packet. Mode events and data events
-/// are separate: `EnteredRx` / `EnteredTx` / `Idle` describe what the radio
-/// is *doing now*, while `PacketRx` / `PacketTx` describe *what just
-/// happened* without implying a mode change.
+/// Radio-to-host outbound channel (depth 32: enough to hold a burst of
+/// RX events + queued command responses without stalling the radio ISR).
+pub type OutboundChannel = Channel<CriticalSectionRawMutex, OutboundFrame, 32>;
+
+// ── Internal: display commands (no longer wire-visible) ────────────
+
+/// Internal display command routed from host_task to display_task. The
+/// wire protocol no longer carries DisplayOn/Off (`PROTOCOL.md §15.2`);
+/// these values drive the display statechart from local events only.
+#[derive(Debug, Clone, Copy, defmt::Format)]
+#[allow(dead_code)] // `Off` is reserved for future diagnostic paths.
+pub enum DisplayCommand {
+    /// Host connected (DTR rose on USB, or UART came up). Wake display.
+    On,
+    /// Host disconnected. Park display.
+    Off,
+    /// Reset cumulative counters (e.g., on config change).
+    Reset,
+}
+
+/// Host-to-display command channel.
+pub type DisplayCommandChannel = Channel<CriticalSectionRawMutex, DisplayCommand, 4>;
+
+// ── Radio → Display: typed packet/mode events ──────────────────────
+
+/// Radio → downstream typed events. These drive the display; they are
+/// NOT the same thing as `OutboundFrame` (which goes out the host
+/// transport). Mode events describe what the radio is doing now; packet
+/// events describe what just happened.
 #[derive(Debug, Clone, defmt::Format)]
 pub enum RadioEvent {
-    /// Radio is now in RX mode.
     EnteredRx,
-    /// Radio is now in TX mode.
     EnteredTx,
-    /// Radio is now idle.
     Idle,
-    /// A packet was received with these link metrics.
     PacketRx { rssi: i16, snr: Option<i16> },
-    /// A packet was transmitted successfully.
     PacketTx,
-    /// `SetConfig` applied a new validated config.
-    ConfigChanged(RadioConfig),
+    ConfigChanged(LoRaConfig),
 }
 
-/// Radio → Display event stream (depth 32: buffer RX bursts while the
-/// display drains slowly).
 pub type RadioEventChannel = Channel<CriticalSectionRawMutex, RadioEvent, 32>;