iPhone and iPad app: the same features, served from the Frame

An iPhone can't run Python or ssh, but the Frame can. The app (ios/, SwiftUI)
connects with its own SSH key (Citadel), copies the server and helpers to
~/.cache/frame-control/<version> on the Frame once per version, starts
ui/server.py there with FRAME_LOCAL=1 on the Frame's 127.0.0.1, and shows the
page through an SSH tunnel. The server exits when the phone disconnects.

Server: FRAME_LOCAL=1 puts ui/local-bin on PATH, whose ssh stand-in runs each
`ssh frame COMMAND` locally (and serves as rsync's transport), so desktop and
phone share one code path. Android display goes through podman exec there, as
the Frame has no adb. FRAME_UI_KEY replaces the fixed X-Frame-UI value with a
per-session key. Power actions take the Developer Mode password via sudo -S.
--port 0 now prints the port it took.

Page: a bottom tab bar and safe areas on phones, Play buttons visible on touch
screens, saving through the share sheet, SSH/SFTP/Steam Link/remote desktop
opening in their iOS apps, and a password dialog for power.

App: pairing with the Developer Mode password once (never stored) or with a
key the user adds; host key pinned on first use; plain-language connection
errors with quiet retries; frame-control://install links; alerts and confirms.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ios/FrameControl/App/AppModel.swift

@@ -0,0 +1,212 @@
+import Citadel
+import Foundation
+import SwiftUI
+import UIKit
+
+/// The app's one piece of state: which headset, and how far along connecting to it is.
+@MainActor
+final class AppModel: ObservableObject {
+    enum Phase: Equatable {
+        case setup
+        case connecting(String)
+        case ready(URL)
+        case failed(String)
+    }
+
+    @Published private(set) var phase: Phase
+    @Published private(set) var settings: FrameSettings?
+    /// Install links that arrived before the page was ready for them.
+    @Published var pendingInstallLinks: [InstallLink] = []
+
+    private var link: FrameLink?
+    private var server: HeadsetServer?
+    private var forwarder: PortForwarder?
+    private var attempt = 0
+
+    private static let settingsKey = "frame.settings"
+    private static let hostKeyKey = "frame.hostKey"
+
+    init() {
+        let saved = UserDefaults.standard.data(forKey: Self.settingsKey).flatMap { try? JSONDecoder().decode(FrameSettings.self, from: $0) }
+        settings = saved
+        phase = saved == nil ? .setup : .connecting("Connecting")
+    }
+
+    var deviceName: String { UIDevice.current.userInterfaceIdiom == .pad ? "iPad" : "iPhone" }
+    private var hostKey: String? { UserDefaults.standard.string(forKey: Self.hostKeyKey) }
+
+    // MARK: pairing
+
+    /// First time: log in with the Developer Mode password, add this phone's key to
+    /// ~/.ssh/authorized_keys, record the Frame's host key, then connect with the key.
+    func pair(host: String, user: String, password: String) async {
+        guard let target = Self.parse(host: host, user: user) else {
+            phase = .failed("Enter the headset's address and user name.")
+            return
+        }
+        await teardown()
+        attempt += 1
+        let mine = attempt
+        phase = .connecting("Signing in to \(target.host)")
+        let pin = PinnedHostKey(expected: nil)
+        do {
+            let link = try await FrameLink.connect(target, auth: .passwordBased(username: target.user, password: password), hostKey: pin)
+            defer { Task { await link.close() } }
+            guard mine == attempt else { return }
+            phase = .connecting("Adding this \(deviceName)'s key")
+            let line = authorizedKeysLine
+            try await link.check("umask 077; mkdir -p ~/.ssh && touch ~/.ssh/authorized_keys && "
+                                 + "(grep -qxF \(shellQuote(line)) ~/.ssh/authorized_keys || echo \(shellQuote(line)) >> ~/.ssh/authorized_keys)",
+                                 "Couldn't add the key on the Frame")
+            guard let seen = pin.seen else { throw FrameFailure("The Frame didn't show a host key") }
+            UserDefaults.standard.set(seen, forKey: Self.hostKeyKey)
+            UserDefaults.standard.set(try JSONEncoder().encode(target), forKey: Self.settingsKey)
+            settings = target
+        } catch {
+            guard mine == attempt else { return }
+            phase = .failed((error as? FrameFailure)?.message ?? FrameLink.describe(error, host: target.host))
+            return
+        }
+        await connect()
+    }
+
+    /// For someone who added this phone's key to the Frame themselves: no password.
+    /// The Frame's host key is recorded on this first connection.
+    func useKey(host: String, user: String) async {
+        guard let target = Self.parse(host: host, user: user) else {
+            phase = .failed("Enter the headset's address and user name.")
+            return
+        }
+        UserDefaults.standard.removeObject(forKey: Self.hostKeyKey)
+        UserDefaults.standard.set(try? JSONEncoder().encode(target), forKey: Self.settingsKey)
+        settings = target
+        await connect()
+    }
+
+    /// "host", "host:port" or "[v6]:port", plus a user name.
+    static func parse(host: String, user: String) -> FrameSettings? {
+        var target = FrameSettings(host: host.trimmingCharacters(in: .whitespaces), user: user.trimmingCharacters(in: .whitespaces))
+        if target.host.hasPrefix("["), let close = target.host.firstIndex(of: "]") {
+            let rest = target.host[target.host.index(after: close)...]
+            if rest.hasPrefix(":"), let port = Int(rest.dropFirst()) { target.port = port }
+            target.host = String(target.host[target.host.index(after: target.host.startIndex)..<close])
+        } else if target.host.filter({ $0 == ":" }).count == 1, let colon = target.host.lastIndex(of: ":"),
+                  let port = Int(target.host[target.host.index(after: colon)...]) {
+            target.port = port
+            target.host = String(target.host[..<colon])
+        }
+        guard !target.host.isEmpty, !target.user.isEmpty, (1...65535).contains(target.port) else { return nil }
+        return target
+    }
+
+    /// This phone's line for ~/.ssh/authorized_keys on the Frame.
+    var authorizedKeysLine: String {
+        DeviceKey.authorizedKeysLine(DeviceKey.loadOrCreate(), comment: "frame-control@\(deviceName)")
+    }
+
+    /// Forget the headset: back to the pairing screen. The Frame keeps the key line;
+    /// remove it from ~/.ssh/authorized_keys there to revoke this phone.
+    func forget() async {
+        await teardown()
+        UserDefaults.standard.removeObject(forKey: Self.settingsKey)
+        UserDefaults.standard.removeObject(forKey: Self.hostKeyKey)
+        settings = nil
+        phase = .setup
+    }
+
+    func showSetup() {
+        Task { await teardown() }
+        phase = .setup
+    }
+
+    // MARK: connecting
+
+    /// quiet: a background retry, which leaves the failure screen up until it works.
+    func connect(quiet: Bool = false) async {
+        guard let settings else {
+            phase = .setup
+            return
+        }
+        await teardown()
+        attempt += 1
+        let mine = attempt
+        func step(_ s: String) { if mine == attempt && !quiet { phase = .connecting(s) } }
+        step("Connecting to \(settings.host)")
+        do {
+            let bundle = try HeadsetServer.Bundle.fromApp()
+            let auth = SSHAuthenticationMethod.ed25519(username: settings.user, privateKey: DeviceKey.loadOrCreate())
+            let pin = PinnedHostKey(expected: hostKey)
+            let link = try await FrameLink.connect(settings, auth: auth, hostKey: pin)
+            guard mine == attempt else { await link.close(); return }
+            self.link = link
+            if hostKey == nil, let seen = pin.seen { UserDefaults.standard.set(seen, forKey: Self.hostKeyKey) }
+            let dir = try await HeadsetServer.deploy(bundle, over: link) { s in Task { @MainActor in step(s) } }
+            step("Starting Frame Control on the headset")
+            let key = Self.randomKey()
+            let server = try await HeadsetServer.start(in: dir, over: link, key: key, device: deviceName)
+            self.server = server
+            let forwarder = try await PortForwarder.start(over: link, to: server.port)
+            self.forwarder = forwarder
+            guard mine == attempt else { return }
+            server.onExit = { [weak self] tail in
+                Task { @MainActor in self?.lost(mine, "Frame Control on the headset stopped. \(tail.suffix(200))") }
+            }
+            readySince = Date()
+            phase = .ready(URL(string: "http://127.0.0.1:\(forwarder.localPort)/?key=\(key)")!)
+        } catch {
+            guard mine == attempt else { return }
+            await teardown()
+            phase = .failed((error as? FrameFailure)?.message ?? FrameLink.describe(error, host: settings.host))
+            // Keep trying quietly while the app is open: the Frame may just be asleep.
+            // A new task each time, so retrying for hours doesn't nest awaits.
+            Task { [weak self] in
+                try? await Task.sleep(nanoseconds: 10_000_000_000)
+                guard let self, mine == self.attempt, case .failed = self.phase,
+                      UIApplication.shared.applicationState == .active else { return }
+                await self.connect(quiet: true)
+            }
+        }
+    }
+
+    /// Called when the app comes back to the foreground: iOS may have dropped the
+    /// connection while it was in the background.
+    func resume() {
+        switch phase {
+        case .ready:
+            if link?.isConnected != true || server?.exited != nil { Task { await connect() } }
+        case .failed:
+            if settings != nil { Task { await connect() } }
+        default:
+            break
+        }
+    }
+
+    private var readySince = Date.distantPast
+
+    private func lost(_ which: Int, _ why: String) {
+        guard which == attempt, case .ready = phase else { return }
+        // Restart it once; if it dies again straight away, say so instead of looping.
+        if Date().timeIntervalSince(readySince) < 20 {
+            Task { await teardown() }
+            phase = .failed(why)
+        } else {
+            Task { await connect() }
+        }
+    }
+
+    private func teardown() async {
+        forwarder?.stop()
+        forwarder = nil
+        server = nil
+        if let link {
+            self.link = nil
+            await link.close()  // ends the server too: its stdin closes
+        }
+    }
+
+    private static func randomKey() -> String {
+        var bytes = [UInt8](repeating: 0, count: 24)
+        _ = SecRandomCopyBytes(kSecRandomDefault, bytes.count, &bytes)
+        return bytes.map { String(format: "%02x", $0) }.joined()
+    }
+}