Keep a simulated location alive outside the map screen

The simulated location only held while the map screen was visible and the app
was foregrounded. The resend loop was a main-runloop Timer in the view's
@State, and .onDisappear tore it down along with the background assertion — so
switching tabs, locking the phone, or ~30s of background each stopped the
resends, let the simulation connection die, and snapped the device back to its
real location.

- Add LocationSimulationKeepAlive, which owns the held coordinate, resends it
  from a dispatch timer instead of the main runloop, takes forced audio and
  location holds (so it works with the user's keep-alive toggles off), and
  renews its background assertion rather than letting it expire.
- MapSelectionView delegates the resend loop to the service, and .onDisappear
  no longer stops the simulation — only an explicit Clear releases it. On
  reappear the view re-adopts the held coordinate so the UI is not misleading.
- MainTabView's URL-scheme path holds on simulate, and releases *before*
  clearing so a queued resend cannot re-apply a location just cleared.

This is the part of the reliability problem the PR never addressed: its
network-path work only governs the JIT/debug tunnel, while location simulation
runs over its own separate rp_pairing connection.

Not verified on device — the background-suspension behaviour needs testing on
real hardware.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

StikDebug/Services/LocationSimulationKeepAlive.swift

@@ -0,0 +1,204 @@
+//
+//  LocationSimulationKeepAlive.swift
+//  StikDebug
+//
+
+import CoreLocation
+import Foundation
+import UIKit
+
+/// Owns the lifetime of an active simulated location, independently of any view.
+///
+/// The device drops a simulated location if nothing keeps pushing it, so the
+/// coordinate has to be re-sent periodically. That resend loop used to live in
+/// `LocationSimulationView`'s `@State` as a main-runloop `Timer`, torn down by
+/// `.onDisappear` — which tied the simulation's lifetime to the map screen being
+/// visible and the app being foregrounded. Leaving the map tab, locking the
+/// phone, or roughly thirty seconds of background were each enough to stop the
+/// resends, let the simulation connection die, and snap the device back to its
+/// real location.
+///
+/// This keeps the coordinate outside the view, resends it from a dispatch timer
+/// rather than the main runloop, holds the keep-alive services for as long as a
+/// simulation is active, and renews its background assertion instead of letting
+/// it expire.
+final class LocationSimulationKeepAlive {
+    static let shared = LocationSimulationKeepAlive()
+
+    /// The device drops the simulation if it goes unrefreshed; this matches the
+    /// interval the view's timer used.
+    private static let resendInterval: TimeInterval = 4
+
+    private let stateLock = NSLock()
+    private let timerQueue = DispatchQueue(label: "com.stik.location-keepalive")
+
+    private var coordinate: CLLocationCoordinate2D?
+    private var timer: DispatchSourceTimer?
+    private var isHolding = false
+
+    /// Main-thread only, mirroring `DebugKeepAliveLease`.
+    private var backgroundTaskID: UIBackgroundTaskIdentifier = .invalid
+
+    private init() {}
+
+    var isActive: Bool {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+        return coordinate != nil
+    }
+
+    var activeCoordinate: CLLocationCoordinate2D? {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+        return coordinate
+    }
+
+    /// Begin holding `newCoordinate`, or retarget an existing hold.
+    ///
+    /// Safe to call repeatedly: the keep-alive is acquired once and the resend
+    /// timer is created once, no matter how many times the coordinate changes.
+    func hold(_ newCoordinate: CLLocationCoordinate2D) {
+        stateLock.lock()
+        let isFirstHold = coordinate == nil
+        coordinate = newCoordinate
+        stateLock.unlock()
+
+        acquireKeepAlive()
+        startTimer()
+
+        if isFirstHold {
+            LogManager.shared.addInfoLog("Holding simulated location (resending every \(Int(Self.resendInterval))s)")
+        }
+    }
+
+    /// Stop holding a simulated location and release the keep-alive.
+    ///
+    /// This does **not** clear the simulation on the device — callers that want
+    /// the real location back must still call `clear_simulated_location()`.
+    func release() {
+        stateLock.lock()
+        let wasActive = coordinate != nil
+        coordinate = nil
+        timer?.cancel()
+        timer = nil
+        stateLock.unlock()
+
+        releaseKeepAlive()
+
+        if wasActive {
+            LogManager.shared.addInfoLog("Released simulated location hold")
+        }
+    }
+
+    // MARK: - Resend loop
+
+    private func startTimer() {
+        // Built and installed under the lock so a losing racer never creates a
+        // source it has to throw away — a timer source starts suspended, and
+        // deallocating a suspended source traps.
+        stateLock.lock()
+        guard timer == nil else {
+            stateLock.unlock()
+            return
+        }
+
+        let source = DispatchSource.makeTimerSource(queue: timerQueue)
+        source.schedule(
+            deadline: .now() + Self.resendInterval,
+            repeating: Self.resendInterval,
+            leeway: .milliseconds(500)
+        )
+        source.setEventHandler { [weak self] in
+            self?.resend()
+        }
+        timer = source
+        stateLock.unlock()
+
+        source.resume()
+    }
+
+    private func resend() {
+        guard let target = activeCoordinate else { return }
+
+        // `simulate_location` reuses its cached connection and rebuilds it if the
+        // set fails, so a dropped tunnel (e.g. a Wi-Fi<->cellular handoff) heals
+        // on the next tick. A failure here is expected and transient; the next
+        // resend retries.
+        LocationSimulationCommandQueue.shared.async {
+            _ = simulate_location(
+                DeviceConnectionContext.targetIPAddress,
+                target.latitude,
+                target.longitude,
+                PairingFileStore.prepareURL().path
+            )
+        }
+    }
+
+    // MARK: - Keep-alive
+
+    private func acquireKeepAlive() {
+        stateLock.lock()
+        let alreadyHolding = isHolding
+        isHolding = true
+        stateLock.unlock()
+
+        guard !alreadyHolding else { return }
+
+        runOnMain {
+            // Forced holds: an active simulation must keep the app running even
+            // if the user's keep-alive toggles are off, otherwise iOS suspends us
+            // and the resends stop.
+            BackgroundAudioManager.shared.requestStart(force: true)
+            BackgroundLocationManager.shared.requestStart(force: true)
+            self.beginBackgroundTask()
+        }
+    }
+
+    private func releaseKeepAlive() {
+        stateLock.lock()
+        let wasHolding = isHolding
+        isHolding = false
+        stateLock.unlock()
+
+        guard wasHolding else { return }
+
+        runOnMain {
+            BackgroundAudioManager.shared.requestStop(force: true)
+            BackgroundLocationManager.shared.requestStop(force: true)
+            self.endBackgroundTask()
+        }
+    }
+
+    // MARK: - Background task (main-thread only)
+
+    private func beginBackgroundTask() {
+        endBackgroundTask()
+        backgroundTaskID = UIApplication.shared.beginBackgroundTask(withName: "StikDebugLocationSimulation") { [weak self] in
+            guard let self else { return }
+            // Silent audio is what actually sustains background execution, so do
+            // not tear the hold down when this assertion expires — take a fresh
+            // one and keep resending.
+            if self.isActive {
+                LogManager.shared.addInfoLog("Location simulation background window renewed")
+                self.beginBackgroundTask()
+            } else {
+                self.endBackgroundTask()
+            }
+        }
+    }
+
+    private func endBackgroundTask() {
+        if backgroundTaskID != .invalid {
+            UIApplication.shared.endBackgroundTask(backgroundTaskID)
+            backgroundTaskID = .invalid
+        }
+    }
+
+    private func runOnMain(_ work: @escaping () -> Void) {
+        if Thread.isMainThread {
+            work()
+        } else {
+            DispatchQueue.main.async(execute: work)
+        }
+    }
+}

StikDebug/Views/MainTabView.swift

@@ -7,6 +7,7 @@
 
 import SwiftUI
 import Foundation
+import CoreLocation
 
 private enum ExternalLocationAction: Identifiable {
     case simulate(URL, Double, Double)
@@ -223,6 +224,14 @@ struct MainTabView: View {
 
             DispatchQueue.main.async {
                 if code == 0 {
+                    // Hold it, so a URL-scheme simulation survives backgrounding
+                    // the same way one set from the map does.
+                    LocationSimulationKeepAlive.shared.hold(
+                        CLLocationCoordinate2D(
+                            latitude: coordinate.latitude,
+                            longitude: coordinate.longitude
+                        )
+                    )
                     BackgroundLocationManager.shared.requestStart()
                     LogManager.shared.addInfoLog(
                         String(format: "Simulated location from URL: %.6f, %.6f", coordinate.latitude, coordinate.longitude)
@@ -239,6 +248,9 @@ struct MainTabView: View {
     }
 
     private func clearSimulatedLocation() {
+        // Release before clearing: a queued resend would otherwise re-apply the
+        // location a few seconds after it was cleared.
+        LocationSimulationKeepAlive.shared.release()
         LocationSimulationCommandQueue.shared.async {
             let code = clear_simulated_location()
             DispatchQueue.main.async {

StikDebug/Views/MapSelectionView.swift

@@ -728,7 +728,6 @@ struct LocationSimulationView: View {
     @State private var position: MapCameraPosition = .userLocation(fallback: .automatic)
 
     @State private var backgroundTaskID: UIBackgroundTaskIdentifier = .invalid
-    @State private var resendTimer: Timer?
     @State private var routeLoadTask: Task<Void, Never>?
     @State private var routeSpeedPrefetchTask: Task<Void, Never>?
     @State private var routePlaybackTask: Task<Void, Never>?
@@ -1025,6 +1024,14 @@ struct LocationSimulationView: View {
         }
         .onAppear {
             loadBookmarks()
+            // The hold outlives this view now, so @State can come back empty
+            // while a simulation is still running. Re-adopt it so the UI shows
+            // the active location instead of looking idle.
+            if simulatedCoordinate == nil,
+               let held = LocationSimulationKeepAlive.shared.activeCoordinate {
+                simulatedCoordinate = held
+                coordinate = held
+            }
         }
         .onDisappear {
             routeLoadTask?.cancel()
@@ -1032,7 +1039,9 @@ struct LocationSimulationView: View {
             routeSpeedPrefetchTask?.cancel()
             routeSpeedPrefetchTask = nil
             cancelRoutePlayback(resetMarker: true)
-            stopResendLoop()
+            // Deliberately does NOT stop the simulation. A held location has to
+            // outlive this screen — leaving the tab used to snap the device back
+            // to its real location. Only an explicit Clear releases the hold.
             if backgroundTaskID != .invalid {
                 BackgroundLocationManager.shared.requestStop()
             }
@@ -1379,18 +1388,13 @@ struct LocationSimulationView: View {
 
     private func startResendLoop(with coordinate: CLLocationCoordinate2D) {
         simulatedCoordinate = coordinate
-        resendTimer?.invalidate()
+        // Owned by the service, not this view: a main-runloop Timer stops when
-        resendTimer = Timer.scheduledTimer(withTimeInterval: 4, repeats: true) { _ in
+        // the app is suspended, and @State dies with the screen.
-            guard let simulatedCoordinate else { return }
+        LocationSimulationKeepAlive.shared.hold(coordinate)
-            LocationSimulationCommandQueue.shared.async {
-                _ = locationUpdateCode(for: simulatedCoordinate)
-            }
-        }
     }
 
     private func stopResendLoop() {
-        resendTimer?.invalidate()
+        LocationSimulationKeepAlive.shared.release()
-        resendTimer = nil
         simulatedCoordinate = nil
     }