[carplay] Keep the GPS fix alive while another nav app holds the CarPlay screen #15

Repro: launch CoMaps from CarPlay, switch the CarPlay screen to Apple Maps
and start navigation, switch to Google Maps and start navigation, wait a
couple of minutes, then switch back to CoMaps. CoMaps' CarPlay map has lost
its position fix and the blue dot never recovers — until the phone is
unlocked and the CoMaps phone app is foregrounded, at which point the fix
returns immediately.
Root cause (confirmed in code and in device/simulator logs that show both
CarPlay scene callbacks firing with activationState == 0 / .unattached):
the framework and location lifecycle were keyed off a CarPlay scene's
activationState, which UIKit reports unreliably. Three distinct gaps
combined to produce the symptom.
1. Location was killed while the map was hosted on a CarPlay screen.
 When the phone is locked (or otherwise not foreground), the phone scene's
 sceneWillResignActive checked SceneLifecycle.isAnyCarSceneForegroundActive,
 which requires a CarPlay scene to report .foregroundActive. Because that
 state is unreliable (the app scene stays .foregroundInactive in the
 simulator and dashboard<->app handoffs race), the guard failed, the full
 resign path ran, keepRunningInBackground() returned NO (CoMaps itself was
 not routing), and location was stopped — logged as "Stop updating
 location" even though the map was on the car screen.
2. Background location updates were never enabled for the CarPlay case.
 allowsBackgroundLocationUpdates was set only inside applicationWillResignActive,
 and keepRunningInBackground() only returned YES when CoMaps itself was
 routing or GPS-tracking. With the user navigating in Apple/Google Maps —
 not CoMaps — CoMaps was a fully backgrounded app with background updates
 disabled, so iOS suspended it and stopped delivering fixes; the cached
 fix went stale over the couple of minutes the other app held the screen.
3. Location was never restarted on the CarPlay foreground path.
 carSceneDidBecomeActive() restored rendering and focus but never called
 applicationDidBecomeActive. Only the phone scene's sceneDidBecomeActive
 (re)started location — which is exactly why the fix recovered only after
 foregrounding the phone app, and not when switching back to CoMaps on
 CarPlay.
Fix, in three parts:
Part A — key the lifecycle on stable host state instead of activationState.
 - CarPlayService.isHostingMapOnCarScreen (mapHost == .carplay/.dashboard),
 which only flips when the map view is actually re-parented.
 - SceneLifecycle.shouldKeepForeground = phone scene foregroundActive
 (reliable for a normal app scene) OR isHostingMapOnCarScreen.
 - SceneDelegate.sceneWillResignActive keeps the framework and location
 alive based on isHostingMapOnCarScreen.
 - leaveForegroundIfNoSceneActive() runs the full background transition
 (onGetFocus(false) + applicationWillResignActive + EnterBackground) and
 is invoked from both carSceneDidEnterBackground and the end of
 CarPlayService.destroy(), so it is robust to UIKit skipping
 sceneDidEnterBackground for a disconnecting CarPlay scene (which would
 otherwise leave rendering and GPS running on a locked phone).
 This half mirrors the approach from the earlier, un-merged commit
 578b9ef2d2 on the carplay-background-host-state branch.
Part B — keep background location alive while CarPlay hosts the map.
 - keepRunningInBackground() now also returns YES while
 isHostingMapOnCarScreen, so CoMaps stays eligible for background
 location and is not suspended when another CarPlay nav app takes the
 screen with the phone locked.
 - The allowsBackgroundLocationUpdates policy is centralized in
 applyBackgroundLocationUpdatesPolicy and applied on BOTH lifecycle edges
 (applicationDidBecomeActive and applicationWillResignActive), not just on
 resign, so the CarPlay-hosted case enables background updates when
 location starts. The flag reverts to NO on CarPlay disconnect, when
 keepRunningInBackground() again returns NO.
Part C — restart location on the CarPlay foreground path.
 - carSceneDidBecomeActive() now also calls
 LocationManager.applicationDidBecomeActive(), mirroring the phone scene.
 This recovers the fix if the app was suspended while another nav app held
 the screen, and (with Part B) re-asserts the background-updates policy.
 Shared by both the CarPlay app and dashboard scene delegates.
Safety for phone-only users: when CarPlay is disconnected,
isHostingMapOnCarScreen is false and keepRunningInBackground() is unchanged,
so normal phone backgrounding still stops location when not routing — no
battery regression.
Also logs the framework EnterForeground/EnterBackground transitions and the
keep/leave-foreground decisions, which were previously invisible.
Verification requires a real device (the simulator cannot switch between
CarPlay apps and reports kCLErrorDenied artifacts): reproduce the sequence
above and confirm the blue dot is live the instant CoMaps returns to the
CarPlay screen without touching the phone; confirm location still stops on
CarPlay disconnect on a locked phone, and still stops on a plain phone lock
when not routing.
Generated with Claude Code Opus 4.8
Signed-off-by: eisa01 <eisa01@gmail.com>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>