feat: peer version exchange with soft-warn UI indicator

Adds a one-shot Hello message to the lan-mouse wire protocol so each
peer can display the other end's build commit hash and warn on
version mismatch. Soft-warn only — mismatched versions never refuse
traffic.

Wire change (lan-mouse-proto)
* `ProtoEvent::Hello { commit: [u8; 8] }` carries the 8-byte ASCII
  short commit from shadow_rs's `SHORT_COMMIT`. Encoded/decoded
  alongside the existing event variants.
* `EventType::Hello` is appended to the enum so existing IDs are
  untouched. Old peers receive the event, hit `InvalidEventId`, and
  silently skip it via the forward-compat handler in
  `connect.rs::receive_loop` — the connection is unaffected.

Daemon
* Connect side sends one Hello immediately after the DTLS handshake
  authenticates and before the ping_pong loop starts. Best-effort,
  fire-and-forget — `log::debug!` on send error.
* Listen side mirrors the peer's Hello with its own (same shape as
  the existing Ping → Pong reply), so the peer's connect-side
  receive_loop populates `ClientState::peer_commit` for that
  handle.
* The disconnect path clears `peer_commit` so a stale hash isn't
  shown after the connection drops.

IPC
* `ClientState::peer_commit: Option<[u8; 8]>`. `None` means the
  peer hasn't sent Hello yet — either fresh connection or older
  build that predates the event.

GTK
* `ClientObject` exposes `peer-commit` as an `Option<String>`
  property; `peer_commit_to_string` converts the wire `[u8; 8]` to
  the displayable hex.
* `lan_mouse_gtk::run` now takes the local commit and stashes it in
  a `OnceLock` so per-row UI can compare against each peer's hash.
* `ClientRow::refresh_version_status` re-renders the collapsed
  subtitle with Pango markup whenever the property changes:
   - matched → green   "peer version: <hex> · matched"
   - mismatch → orange "peer version: <hex> · ours: <hex>"
   - unknown → orange  "peer version: unknown · ours: <hex>"
* Window invokes `refresh_version_status` from
  `update_client_state` after writing the new property, and
  `bind` calls it once on row construction so the initial
  subtitle isn't blank.

Known limitation: state-change broadcasts from the network side
(set_alive / set_active_addr / set_peer_commit) don't currently
trigger a `FrontendEvent::State` directly; the UI picks up the
latest values on the next user-driven broadcast. Same pre-existing
behavior as the alive/active_addr fields.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/client.rs

@@ -282,6 +282,12 @@ impl ClientManager {
         }
     }
 
+    pub(crate) fn set_peer_commit(&self, handle: ClientHandle, commit: Option<[u8; 8]>) {
+        if let Some((_, s)) = self.clients.borrow_mut().get_mut(handle as usize) {
+            s.peer_commit = commit;
+        }
+    }
+
     pub(crate) fn active_addr(&self, handle: ClientHandle) -> Option<SocketAddr> {
         self.clients
             .borrow()

src/config.rs

@@ -28,6 +28,18 @@ use shadow_rs::shadow;
 
 shadow!(build);
 
+/// Local build's 8-byte ASCII short commit hash, suitable for use
+/// in [`lan_mouse_proto::ProtoEvent::Hello`]. Pads with `'?'` if
+/// shadow_rs returns an unexpected length so the field is always
+/// well-formed on the wire.
+pub fn local_commit() -> [u8; 8] {
+    let bytes = build::SHORT_COMMIT.as_bytes();
+    let mut out = [b'?'; 8];
+    let n = bytes.len().min(8);
+    out[..n].copy_from_slice(&bytes[..n]);
+    out
+}
+
 const CONFIG_FILE_NAME: &str = "config.toml";
 const CERT_FILE_NAME: &str = "lan-mouse.pem";
 

src/connect.rs

@@ -1,4 +1,5 @@
 use crate::client::ClientManager;
+use crate::config::local_commit;
 use lan_mouse_ipc::{ClientHandle, DEFAULT_PORT};
 use lan_mouse_proto::{MAX_EVENT_SIZE, ProtoEvent};
 use local_channel::mpsc::{Receiver, Sender, channel};
@@ -197,6 +198,16 @@ async fn connect_to_handle(
         conns.lock().await.insert(addr, conn.clone());
         connecting.lock().await.remove(&handle);
 
+        // Best-effort version handshake. Send our commit hash once
+        // immediately after the DTLS handshake; the listen side
+        // mirrors a Hello back so the receive loop can populate
+        // `peer_commit`. Old peers will silently skip this event
+        // per the forward-compat handler in [`receive_loop`].
+        let (buf, len) = ProtoEvent::Hello { commit: local_commit() }.into();
+        if let Err(e) = conn.send(&buf[..len]).await {
+            log::debug!("hello send to {addr} failed: {e}");
+        }
+
         // poll connection for active
         spawn_local(ping_pong(addr, conn.clone(), ping_response.clone()));
 
@@ -264,6 +275,9 @@ async fn receive_loop(
                         client_manager.set_alive(handle, b);
                         ping_response.borrow_mut().insert(addr);
                     }
+                    ProtoEvent::Hello { commit } => {
+                        client_manager.set_peer_commit(handle, Some(commit));
+                    }
                     event => tx.send((handle, event)).expect("channel closed"),
                 }
             }
@@ -287,6 +301,7 @@ async fn disconnect(
     log::warn!("client ({handle}) @ {addr} connection closed");
     conns.lock().await.remove(&addr);
     client_manager.set_active_addr(handle, None);
+    client_manager.set_peer_commit(handle, None);
     let active: Vec<SocketAddr> = conns.lock().await.keys().copied().collect();
     log::info!("active connections: {active:?}");
 }

src/emulation.rs

@@ -1,3 +1,4 @@
+use crate::config::local_commit;
 use crate::listen::{LanMouseListener, ListenEvent, ListenerCreationError};
 use futures::StreamExt;
 use input_emulation::{EmulationHandle, InputEmulation, InputEmulationError};
@@ -150,6 +151,16 @@ impl ListenTask {
                             }
                             ProtoEvent::Input(event) => self.emulation_proxy.consume(event, addr),
                             ProtoEvent::Ping => self.listener.reply(addr, ProtoEvent::Pong(self.emulation_proxy.emulation_active.get())).await,
+                            // Mirror the peer's version handshake. The
+                            // outgoing connect side initiated this with
+                            // its own Hello; we echo ours back so the
+                            // peer's connect-side receive_loop can
+                            // populate `peer_commit`. We don't store
+                            // the peer's commit on the listen side —
+                            // the user-visible state lives on outgoing
+                            // connections, where the same peer is also
+                            // configured as a `[[clients]]` entry.
+                            ProtoEvent::Hello { .. } => self.listener.reply(addr, ProtoEvent::Hello { commit: local_commit() }).await,
                             _ => {}
                         }
                     }

src/main.rs

@@ -74,7 +74,7 @@ fn run() -> Result<(), LanMouseError> {
             #[cfg(feature = "gtk")]
             {
                 let mut service = start_service()?;
-                let res = lan_mouse_gtk::run();
+                let res = lan_mouse_gtk::run(config::local_commit());
                 #[cfg(unix)]
                 {
                     // on unix we give the service a chance to terminate gracefully