macos: Nearby-devices picker (AirDrop-style) over the LAN

Add a horizontal strip of discovered tether devices to the window: the store
polls engine.nearby() every 2s while connected and renders each as a chip with
its friendly name + platform icon. Tapping a device calls pair() — sets room to
that device's room and reconnects, so you join it without typing a room id.
Devices already in your room show "in your room" (disabled).

Verified live on macOS: two named LAN devices appear as "tap to join" chips
once the app has Local Network permission.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ios/MacTetherApp/Sources/ContentView.swift

@@ -8,6 +8,10 @@ struct ContentView: View {
         VStack(spacing: 0) {
             toolbar
             Divider()
+            if store.connected && !store.nearby.isEmpty {
+                nearbyStrip
+                Divider()
+            }
             feedArea
             Divider()
             composer
@@ -16,6 +20,40 @@ struct ContentView: View {
         .task { store.connectIfSaved() }
     }
 
+    // MARK: - Nearby devices (AirDrop-style picker)
+
+    private var nearbyStrip: some View {
+        ScrollView(.horizontal, showsIndicators: false) {
+            HStack(spacing: 8) {
+                Label("Nearby", systemImage: "dot.radiowaves.left.and.right")
+                    .font(.caption).foregroundStyle(.secondary)
+                    .padding(.trailing, 4)
+                ForEach(store.nearby, id: \.id) { peer in
+                    let here = peer.room == store.room
+                    Button {
+                        store.pair(with: peer)
+                    } label: {
+                        HStack(spacing: 6) {
+                            Image(systemName: sourceIcon(peer.source))
+                            VStack(alignment: .leading, spacing: 1) {
+                                Text(peer.name).font(.caption).lineLimit(1)
+                                Text(here ? "in your room" : "tap to join")
+                                    .font(.caption2)
+                                    .foregroundStyle(here ? .green : .secondary)
+                            }
+                        }
+                        .padding(.horizontal, 10).padding(.vertical, 6)
+                        .background(Color.primary.opacity(0.06), in: Capsule())
+                    }
+                    .buttonStyle(.plain)
+                    .disabled(here)
+                    .help(here ? "Already in this room" : "Join \(peer.name)'s room")
+                }
+            }
+            .padding(.horizontal, 12).padding(.vertical, 6)
+        }
+    }
+
     // MARK: - Toolbar
 
     private var toolbar: some View {

ios/MacTetherApp/Sources/MacTetherStore.swift

@@ -19,6 +19,7 @@ final class MacTetherStore {
     var serverURL: String = UserDefaults.standard.string(forKey: "serverURL") ?? "https://tether.pecord.io"
     var room: String = RoomIdentity.derive()
     var feed: [FeedItem] = []
+    var nearby: [Peer] = []   // tether devices on the LAN, for the picker
     var connected = false
     var lastError: String?
     var hasAttemptedConnect = false
@@ -27,6 +28,7 @@ final class MacTetherStore {
     private var engine: Engine?
     private var bridge: EngineBridge?
     private var pollTask: Task<Void, Never>?
+    private var nearbyTask: Task<Void, Never>?
     private var lastChangeCount = NSPasteboard.general.changeCount
 
     func connectIfSaved() {
@@ -53,6 +55,15 @@ final class MacTetherStore {
         connected = true
         lastError = nil
 
+        // Poll the engine's mDNS-discovered device list for the picker.
+        nearbyTask = Task { [weak self] in
+            while !Task.isCancelled {
+                try? await Task.sleep(for: .seconds(2))
+                guard let self, let engine = self.engine else { continue }
+                self.nearby = engine.nearby().sorted { $0.name < $1.name }
+            }
+        }
+
         // Send: poll NSPasteboard for local changes → push to room.
         lastChangeCount = NSPasteboard.general.changeCount
         pollTask = Task { [weak self] in
@@ -75,9 +86,18 @@ final class MacTetherStore {
         bridge = nil
         pollTask?.cancel()
         pollTask = nil
+        nearbyTask?.cancel()
+        nearbyTask = nil
+        nearby = []
         connected = false
     }
 
+    /// Join a discovered device's room — the "pair" action from the picker.
+    func pair(with peer: Peer) {
+        room = peer.room
+        connect()
+    }
+
     func send(_ text: String) {
         engine?.send(text: text)
     }