feat(apple/M2): opt-in background keep-alive (audio + video-drop + timeout)

Backgrounding a live session no longer freezes it when the user opts in: audio keeps playing (UIBackgroundModes audio), the QUIC connection + pump stay live, video decode is DROPPED, and a bounded timer auto-disconnects. Off by default. - PunktfunkConnection.setVideoDropped/isVideoDropped: a tiny lock-guarded flag both pumps read every iteration. StreamPump (stage-1), Stage2Pipeline (VT + PyroWave) drain nextAU() for flow control but DISCARD the AU before any VideoToolbox/Metal work — the crash/jetsam-safe seam (no GPU off-screen). - SessionModel.enterBackground(timeoutMinutes:) / exitBackground(): set the drop flag, mute the mic (privacy — SessionAudio.setMicMuted pauses the capture engine), arm a DispatchSourceTimer that disconnect(deliberate:false)s on fire (keeps host linger → fast late reconnect). exitBackground clears the flag and requestKeyframe()s; the pump's freeze gate auto-arms on the resumed frame-index gap so concealed frames are withheld until the IDR re-anchors. disconnect() cancels the timer + clears isBackgrounded. - ContentView scenePhase driver (iOS): .background+streaming+setting → enterBackground; .active → exitBackground. scenePhase (not willResignActive) so Control-Center/app-switcher peeks don't start the timer. - Settings → General (iOS-only keepAliveSection): toggle + 1/5/10/30 timeout; new keys backgroundKeepAlive (def off) / backgroundTimeoutMinutes (def 10). - Info.plist: UIBackgroundModes [audio] + NSSupportsLiveActivities (for M3). macOS swift build + swift test green (142 tests). The iOS-gated scenePhase handler + settings section are not exercised by the macOS CI target (known §9 gap) — need on-glass verification (audio never gaps, video re-anchors <1s LAN, timeout ends the session, phone-call audio-steal degrades gracefully). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-07-16 18:41:46 +02:00
parent 4cae1b8bb8
commit 14c5e7c11c
10 changed files with 187 additions and 0 deletions
@@ -96,6 +96,14 @@ struct ContentView: View {
    /// fires Wake-on-LAN up front and falls into the "Waking…" wait if the dial fails. Off: connects
    /// go straight through with no wake. The explicit "Wake Host" action is unaffected either way.
    @AppStorage(DefaultsKey.autoWake) private var autoWakeEnabled = true
+    /// Background keep-alive (Settings → General, iOS-only). Default OFF (today's freeze-on-background
+    /// is the default). When on, backgrounding a live session keeps audio + the connection alive and
+    /// drops video, auto-disconnecting after `backgroundTimeoutMinutes`.
+    @AppStorage(DefaultsKey.backgroundKeepAlive) private var backgroundKeepAlive = false
+    @AppStorage(DefaultsKey.backgroundTimeoutMinutes) private var backgroundTimeoutMinutes = 10
+    /// scenePhase drives the keep-alive: use THIS, not the willResignActive observers — resign-active
+    /// also fires for Control Center / app-switcher peeks, where the disconnect timer must not start.
+    @Environment(\.scenePhase) private var scenePhase
    private var gamepadUIActive: Bool {
        GamepadUIEnvironment.isActive(
            gamepadConnected: gamepadManager.active != nil, enabledSetting: gamepadUIEnabled)
@@ -122,6 +130,22 @@ struct ContentView: View {
        // tap uses, so trust policy / WoL / the approval sheet all come along. Never starts a
        // parallel session — this drives the one `model` ContentView owns.
        .onOpenURL { handleDeepLink($0) }
+        #if os(iOS)
+        // Background keep-alive driver (opt-in). Only .background/.active matter; .inactive (a
+        // transient peek) is ignored so the disconnect timer never starts for a Control-Center pull.
+        .onChange(of: scenePhase) { _, phase in
+            switch phase {
+            case .background:
+                if backgroundKeepAlive, model.phase == .streaming {
+                    model.enterBackground(timeoutMinutes: backgroundTimeoutMinutes)
+                }
+            case .active:
+                model.exitBackground()
+            default:
+                break
+            }
+        }
+        #endif
        .onChange(of: model.phase) { _, phase in
            switch phase {
            case .streaming:
@@ -148,6 +148,13 @@ final class SessionModel: ObservableObject {

    var isBusy: Bool { phase != .idle }

+    /// True while a streaming session is running in the background under the opt-in keep-alive
+    /// (audio plays, video dropped, timeout armed). Drives the Live Activity's stage/countdown (M3)
+    /// and is cleared on foreground or teardown. iOS/iPadOS only in practice.
+    @Published private(set) var isBackgrounded = false
+    /// Bounded auto-disconnect for a backgrounded keep-alive session. Fires on `.main`.
+    private var backgroundTimer: DispatchSourceTimer?
+
    /// `allowTofu` gates the trust-on-first-use prompt for an unpinned host: it is only true
    /// when the host EXPLICITLY advertised `pair=optional` (rule 3a). For any other unpinned host
    /// — `pair=required`, a manually-typed host, or a discovered host with no/unknown `pair`
@@ -332,6 +339,46 @@ final class SessionModel: ObservableObject {
        }
    }

+    // MARK: - Background keep-alive (opt-in, iOS)
+
+    /// Enter the backgrounded keep-alive state: keep audio playing, DROP video decode (no GPU work
+    /// off-screen), mute the mic (privacy), and arm a bounded auto-disconnect. The caller
+    /// (ContentView's scenePhase driver) gates this on the setting + `.streaming`; a no-op otherwise.
+    /// The video-drop seam is read by both pumps every iteration (`connection.isVideoDropped`).
+    func enterBackground(timeoutMinutes: Int) {
+        guard phase == .streaming, let conn = connection, !isBackgrounded else { return }
+        isBackgrounded = true
+        conn.setVideoDropped(true)
+        audio?.setMicMuted(true)
+        // Non-deliberate on fire (keep the host linger) so a user who returns late reconnects fast,
+        // exactly like today's network-drop path. min 1 minute guards a nonsense setting.
+        let minutes = max(1, timeoutMinutes)
+        let timer = DispatchSource.makeTimerSource(queue: .main)
+        timer.schedule(deadline: .now() + .seconds(minutes * 60))
+        timer.setEventHandler { [weak self] in
+            // The timer fires on `.main`, so the actor's executor is the main thread here.
+            MainActor.assumeIsolated { self?.disconnect(deliberate: false) }
+        }
+        backgroundTimer?.cancel()
+        backgroundTimer = timer
+        timer.resume()
+    }
+
+    /// Return to foreground: cancel the timeout, resume mic + video, and force a clean re-anchor —
+    /// request a fresh IDR (infinite GOP: it won't come on its own) and let the pump's freeze gate
+    /// withhold the concealed frames until it lands (it auto-arms on the resumed frame-index gap).
+    func exitBackground() {
+        guard isBackgrounded else { return }
+        isBackgrounded = false
+        backgroundTimer?.cancel()
+        backgroundTimer = nil
+        audio?.setMicMuted(false)
+        if let conn = connection {
+            conn.setVideoDropped(false)
+            conn.requestKeyframe()
+        }
+    }
+
    /// The user confirmed the fingerprint: returns it for pinning and enters streaming.
    func confirmTrust() -> Data? {
        guard case .awaitingTrust(let fingerprint) = phase else { return nil }
@@ -349,6 +396,10 @@ final class SessionModel: ObservableObject {
    func disconnect(deliberate: Bool = true) {
        statsTimer?.invalidate()
        statsTimer = nil
+        // Drop any armed background keep-alive (incl. the timeout that just fired us).
+        backgroundTimer?.cancel()
+        backgroundTimer = nil
+        isBackgrounded = false
        let audio = self.audio
        self.audio = nil
        // Gamepad capture is main-actor (releases held buttons on the wire while the
@@ -440,6 +440,34 @@ extension SettingsView {
        }
    }

+    /// iOS/iPadOS only: keep a backgrounded session alive (audio background mode). Empty elsewhere
+    /// (tvOS backgrounding semantics differ; macOS isn't gated by the mode) so the shared `.general`
+    /// detail can reference it unconditionally.
+    @ViewBuilder var keepAliveSection: some View {
+        #if os(iOS)
+        Section {
+            Toggle("Keep streaming in background", isOn: $backgroundKeepAlive)
+            if backgroundKeepAlive {
+                Picker("Disconnect after", selection: $backgroundTimeoutMinutes) {
+                    Text("1 minute").tag(1)
+                    Text("5 minutes").tag(5)
+                    Text("10 minutes").tag(10)
+                    Text("30 minutes").tag(30)
+                }
+            }
+        } header: {
+            Text("Background")
+        } footer: {
+            Text("Off by default: backgrounding the app freezes the session. When on, audio keeps "
+                + "playing and the connection stays live (video is dropped to save power) after you "
+                + "switch away — and the session auto-disconnects after the time above so it can't "
+                + "run down your battery. Returning to the app resumes video instantly.")
+                .font(.geist(12, relativeTo: .caption))
+                .foregroundStyle(.secondary)
+        }
+        #endif
+    }
+
    @ViewBuilder var experimentalSection: some View {
        Section {
            Toggle("Show game library", isOn: $libraryEnabled)
@@ -49,6 +49,8 @@ struct SettingsView: View {
    @ObservedObject var gamepads = GamepadManager.shared
    @AppStorage(DefaultsKey.gamepadUIEnabled) var gamepadUIEnabled = true
    @AppStorage(DefaultsKey.autoWake) var autoWakeEnabled = true
+    @AppStorage(DefaultsKey.backgroundKeepAlive) var backgroundKeepAlive = false
+    @AppStorage(DefaultsKey.backgroundTimeoutMinutes) var backgroundTimeoutMinutes = 10
    #if DEBUG && !os(tvOS)
    @State var showControllerTest = false
    #endif
@@ -242,6 +244,7 @@ struct SettingsView: View {
                pointerSection
                compositorSection
                wakeSection
+                keepAliveSection // iOS-only content; empty on tvOS
            }
            .formStyle(.grouped)
            .navigationTitle("General")