macos: file/image UI — inline preview, attach to send, reveal in Finder

Wire on_file into the Mac app: received files save to ~/Downloads; images show
an inline preview in the feed, other files show a doc chip with a reveal-in-
Finder button. A paperclip in the composer opens a file picker → send_file
(mime inferred from extension). FeedItem gains optional image/fileURL.

Add `tether-agent send-file <path>` (one-shot share / test helper).

Verified live: an agent sent a 36KB PNG over RTC and it rendered inline in the
Mac app's feed.

Follow-up: iOS file UI (mirror), clipboard-image auto-send, transfer progress.

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

agent/src/main.rs

@@ -96,11 +96,43 @@ fn main() {
         Some("install") => install(),
         Some("uninstall") => uninstall(),
         Some("status") => status(),
+        Some("send-file") => send_file_once(),
         // No subcommand (or --flags) → run in the foreground.
         _ => run(),
     }
 }
 
+/// `tether-agent send-file <path>` — connect, wait for a direct link, send the
+/// file, exit. Handy for testing / one-shot sharing.
+fn send_file_once() {
+    let path = std::env::args()
+        .nth(2)
+        .expect("usage: tether-agent send-file <path> [--server URL --account ID]");
+    let data = std::fs::read(&path).expect("read file");
+    let fname = std::path::Path::new(&path)
+        .file_name()
+        .map(|s| s.to_string_lossy().into_owned())
+        .unwrap_or_else(|| "file".into());
+    let mime = match path.rsplit('.').next().map(str::to_lowercase).as_deref() {
+        Some("png") => "image/png",
+        Some("jpg") | Some("jpeg") => "image/jpeg",
+        Some("gif") => "image/gif",
+        Some("pdf") => "application/pdf",
+        _ => "application/octet-stream",
+    }
+    .to_string();
+
+    let c = config();
+    let engine = Engine::new(c.server, c.room, c.from, c.source, c.name, c.account);
+    engine.start(Box::new(Inbox(Arc::new(Mutex::new(Vec::new())))));
+    eprintln!("connecting + waiting for a direct link…");
+    sleep(Duration::from_secs(10));
+    eprintln!("sending {fname} ({} bytes, {mime})…", data.len());
+    engine.send_file(fname, mime, data);
+    sleep(Duration::from_secs(5)); // let chunks flush
+    eprintln!("done");
+}
+
 fn run() {
     let c = config();
     eprintln!("tether-agent → {}  room={}  source={}", c.server, c.room, c.source);

ios/MacTetherApp/Sources/ContentView.swift

@@ -150,12 +150,21 @@ struct ContentView: View {
     private func feedRow(_ item: FeedItem) -> some View {
         HStack(alignment: .top, spacing: 10) {
             VStack(alignment: .leading, spacing: 4) {
-                Text(item.text)
-                    .font(.body)
-                    .lineLimit(6)
-                    .textSelection(.enabled)
+                if let image = item.image {
+                    Image(nsImage: image)
+                        .resizable().scaledToFit()
+                        .frame(maxWidth: 280, maxHeight: 200)
+                        .clipShape(RoundedRectangle(cornerRadius: 6))
+                } else if item.isFile {
+                    Label(item.text, systemImage: "doc.fill")
+                        .font(.body).lineLimit(1)
+                } else {
+                    Text(item.text)
+                        .font(.body).lineLimit(6).textSelection(.enabled)
+                }
                 HStack {
-                    Label(item.source, systemImage: sourceIcon(item.source))
+                    Label(item.isFile ? "file" : item.source,
+                          systemImage: item.isFile ? "arrow.down.circle" : sourceIcon(item.source))
                         .font(.caption).foregroundStyle(.secondary)
                     Spacer()
                     Text(item.date, style: .time)
@@ -163,13 +172,17 @@ struct ContentView: View {
                 }
             }
             Button {
-                store.copyToPasteboard(item)
+                if let url = item.fileURL {
+                    NSWorkspace.shared.activateFileViewerSelecting([url]) // reveal in Finder
+                } else {
+                    store.copyToPasteboard(item)
+                }
             } label: {
-                Image(systemName: "doc.on.doc")
+                Image(systemName: item.isFile ? "magnifyingglass" : "doc.on.doc")
                     .foregroundStyle(.secondary)
             }
             .buttonStyle(.plain)
-            .help("Copy to clipboard")
+            .help(item.isFile ? "Reveal in Finder" : "Copy to clipboard")
         }
         .padding(10)
         .background(Color.primary.opacity(0.04), in: RoundedRectangle(cornerRadius: 8))
@@ -188,6 +201,15 @@ struct ContentView: View {
 
     private var composer: some View {
         HStack(spacing: 10) {
+            Button {
+                store.attachFile()
+            } label: {
+                Image(systemName: "paperclip")
+            }
+            .buttonStyle(.plain)
+            .disabled(!store.connected)
+            .help("Send a file or image")
+
             TextField("Type a message…", text: $draft, axis: .vertical)
                 .textFieldStyle(.roundedBorder)
                 .lineLimit(1...4)

ios/MacTetherApp/Sources/MacTetherStore.swift

@@ -4,12 +4,15 @@ import enum TetherKit.RoomIdentity   // selective: avoids TetherKit.Message clas
                                      // with the engine's Message (compiled into this target)
 // Engine + Message + MessageHandler come from the generated tethercore.swift.
 
-/// UI-facing clipboard item. Decouples the view from the FFI `Message` record.
-struct FeedItem: Identifiable, Equatable {
+/// UI-facing feed item: a text clipboard, or a received file/image.
+struct FeedItem: Identifiable {
     let id = UUID()
-    let text: String
+    let text: String        // clipboard text, or the file name for files
     let source: String
     let date: Date
+    var image: NSImage? = nil  // preview for image files
+    var fileURL: URL? = nil    // saved location for any received file
+    var isFile: Bool { fileURL != nil }
 }
 
 /// macOS side: drives the shared `tethercore.Engine` (SSE + RTC). Unlike iOS we
@@ -113,6 +116,41 @@ final class MacTetherStore {
         engine?.send(text: text)
     }
 
+    /// Pick a file and send it P2P.
+    func attachFile() {
+        let panel = NSOpenPanel()
+        panel.allowsMultipleSelection = false
+        panel.canChooseDirectories = false
+        guard panel.runModal() == .OK, let url = panel.url,
+              let data = try? Data(contentsOf: url) else { return }
+        engine?.sendFile(name: url.lastPathComponent, mime: Self.mime(for: url.pathExtension), data: data)
+    }
+
+    static func mime(for ext: String) -> String {
+        switch ext.lowercased() {
+        case "png": return "image/png"
+        case "jpg", "jpeg": return "image/jpeg"
+        case "gif": return "image/gif"
+        case "heic": return "image/heic"
+        case "pdf": return "application/pdf"
+        case "txt": return "text/plain"
+        default: return "application/octet-stream"
+        }
+    }
+
+    /// A received file: save to Downloads, preview if it's an image.
+    fileprivate func ingestFile(name: String, mime: String, data: Data, date: Date) {
+        let image: NSImage? = mime.hasPrefix("image/") ? NSImage(data: data) : nil
+        var url: URL?
+        if let downloads = FileManager.default.urls(for: .downloadsDirectory, in: .userDomainMask).first {
+            let dest = downloads.appendingPathComponent(name.isEmpty ? "tether-file" : name)
+            try? data.write(to: dest)
+            url = dest
+        }
+        feed.insert(FeedItem(text: name, source: "file", date: date, image: image, fileURL: url), at: 0)
+        if feed.count > 100 { feed.removeLast() }
+    }
+
     func copyToPasteboard(_ item: FeedItem) {
         writePasteboard(item.text)
     }
@@ -153,6 +191,6 @@ private final class EngineBridge: MessageHandler {
     }
 
     func onFile(name: String, mime: String, data: Data) {
-        // File receive UI is a follow-up; engine handles transport + reassembly.
+        Task { @MainActor in self.store?.ingestFile(name: name, mime: mime, data: data, date: Date()) }
     }
 }