apps: show delivery receipts — "✓ Seen by <device>"

Both apps now poll engine.receipts() alongside nearby() and render a "Seen by
<names>" bar above the composer when acks come in. Closes the loop the receipt
engine opened: you can see your clipboard was received, instead of asking.

Verified live on macOS: copying on the Mac with a peer in the room shows
"✓ Seen by Rust LAN Peer".

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

ios/MacTetherApp/Sources/ContentView.swift

@@ -14,12 +14,30 @@ struct ContentView: View {
             }
             feedArea
             Divider()
+            if !store.receipts.isEmpty {
+                seenByBar
+                Divider()
+            }
             composer
         }
         .frame(minWidth: 480, minHeight: 400)
         .task { store.connectIfSaved() }
     }
 
+    // MARK: - Delivery receipts
+
+    private var seenByBar: some View {
+        let names = Array(Set(store.receipts.map(\.name))).sorted()
+        return HStack(spacing: 6) {
+            Image(systemName: "checkmark.circle.fill")
+                .foregroundStyle(.green).font(.caption)
+            Text("Seen by \(names.joined(separator: ", "))")
+                .font(.caption).foregroundStyle(.secondary).lineLimit(1)
+            Spacer()
+        }
+        .padding(.horizontal, 14).padding(.vertical, 5)
+    }
+
     // MARK: - Nearby devices (AirDrop-style picker)
 
     private var nearbyStrip: some View {

ios/MacTetherApp/Sources/MacTetherStore.swift

@@ -26,6 +26,7 @@ final class MacTetherStore {
     }()
     var feed: [FeedItem] = []
     var nearby: [Peer] = []   // tether devices on the LAN, for the picker
+    var receipts: [Receipt] = []   // delivery acks — "seen by <device>"
     var connected = false
     var lastError: String?
     var hasAttemptedConnect = false
@@ -68,6 +69,7 @@ final class MacTetherStore {
                 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 }
+                self.receipts = engine.receipts()
             }
         }
 

ios/TetherApp/Sources/RoomView.swift

@@ -15,6 +15,10 @@ struct RoomView: View {
                 }
                 feedList
                 Divider()
+                if !store.receipts.isEmpty {
+                    seenByBar
+                    Divider()
+                }
                 composer
             }
             .navigationTitle("tether")
@@ -86,6 +90,18 @@ struct RoomView: View {
         }
     }
 
+    private var seenByBar: some View {
+        let names = Array(Set(store.receipts.map(\.name))).sorted()
+        return HStack(spacing: 6) {
+            Image(systemName: "checkmark.circle.fill")
+                .foregroundStyle(.green).font(.caption)
+            Text("Seen by \(names.joined(separator: ", "))")
+                .font(.caption).foregroundStyle(.secondary).lineLimit(1)
+            Spacer()
+        }
+        .padding(.horizontal, 14).padding(.vertical, 5)
+    }
+
     private func sourceIcon(_ source: String) -> String {
         if source.contains("iphone") || source.contains("ios") { return "iphone" }
         if source.contains("ipad") { return "ipad" }

ios/TetherApp/Sources/TetherStore.swift

@@ -31,6 +31,7 @@ final class TetherStore {
     }()
     var feed: [FeedItem] = []
     var nearby: [Peer] = []   // tether devices on the LAN (empty on iOS w/o multicast entitlement)
+    var receipts: [Receipt] = []   // delivery acks — "seen by <device>"
     var connected = false
     var lastError: String?
 
@@ -67,6 +68,7 @@ final class TetherStore {
                 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 }
+                self.receipts = engine.receipts()
             }
         }
     }