Skill: Background Execution Audit

Purpose

Detects apps that abuse iOS background execution modes — particularly silent audio used to keep the app alive, location background mode used for non-navigation purposes, and background task implementations that do excessive work — enforcing Guideline 2.5.4 which requires background modes to be used only for their intended purpose.

Apple Guideline

• Primary: 2.5.4 — Performance: Multitasking and Background Modes
• Related: 5.1.5
• Reference: references/guidelines/2-performance.md

Real-World Rejection Cases

• Case: App declared the audio background mode and played a silent audio session to prevent the system from suspending the app — rejected under 2.5.4
  Source: Apple Developer Forums (multiple reports)
  Root cause: Playing silent audio in the background solely to prevent app suspension is explicitly prohibited — it abuses the audio background mode, which is intended for apps that provide audible content to the user. Use BGTaskScheduler for background processing instead.

• Case: Fitness app declared location background mode to track user steps, but only needed step count data — Apple reviewer noted the app used CoreLocation for step counting instead of the appropriate CoreMotion/CMPedometer API
  Source: Apple Developer Forums (Guideline 2.5.4 enforcement)
  Root cause: Background location must be used only when the app's core functionality genuinely requires continuous location updates (navigation, geo-fencing). Using it as a workaround to run in the background for non-location tasks violates 2.5.4.

• Case: App declared voip background mode to maintain a persistent socket connection for non-VoIP chat — rejected; VoIP mode is reserved for apps providing telephone-like calling features
  Source: Apple Developer Forums
  Root cause: Each background mode has a specific intended use case — declaring a background mode for a purpose other than its design is treated as abuse. Use BGProcessingTask or BGAppRefreshTask for periodic background work.

Trigger

Invoke on any iOS/macOS project that declares background modes in Info.plist or uses BGTaskScheduler, CLLocationManager, or AVAudioSession.

Inputs

Name	Type	Default	Description
project_root	path	cwd	iOS/macOS project root
shared_context	object	nil	Pre-collected context from appstore-full-audit Phase 1

Actions

Phase 1: Context Collection

Skip this phase if shared_context is provided.

1. Glob **/Info.plist — locate Info.plist for background mode declarations.
2. Glob **/*.swift — collect all Swift source files.

Phase 2: Checks

1. Background audio mode with silent/zero-volume session
   Read Info.plist — check UIBackgroundModes for audio.
   If audio is declared, Grep AVAudioSession|AVAudioPlayer in **/*.swift.
   If audio session category is .ambient or .soloAmbient with no audible content, OR if volume is set to 0 near background mode activation → 🔴 CRITICAL. Silent audio background mode abuse.

2. Background location declared — justify core use
   Read Info.plist — check UIBackgroundModes for location.
   If location is present, Grep CMPedometer|CMMotionActivityManager|CoreMotion in **/*.swift.
   If the app uses CoreMotion/pedometer APIs while also declaring background location → 🟠 HIGH. Step counting and activity tracking belong in CoreMotion, not CoreLocation — background location should not be used as a substitute.

3. VoIP background mode without calling functionality
   Read Info.plist — check UIBackgroundModes for voip.
   If voip is present, Grep CXProvider|CXCallController|CallKit|VoIP in **/*.swift.
   If voip background mode declared but no CallKit integration found → 🔴 CRITICAL. VoIP background mode is reserved for apps providing telephone-like calling via CallKit — using it for persistent socket connections violates 2.5.4.

4. BGTaskScheduler not registered for declared modes
   Grep pattern BGTaskScheduler|BGProcessingTask|BGAppRefreshTask in **/*.swift.
   If background modes fetch or processing are declared but BGTaskScheduler.shared.register is absent → 🟠 HIGH. Background fetch/processing tasks must be registered with BGTaskScheduler — unregistered tasks waste background time and will be deprecated.

5. Location background mode with Always authorization
   Grep pattern requestAlwaysAuthorization in **/*.swift.
   If requestAlwaysAuthorization is called but background location mode is absent from Info.plist → 🟠 HIGH. Requesting Always authorization without declaring background location mode causes the OS to silently downgrade to WhenInUse.

Phase 3: Output

Collect all findings from Phase 2 and build the prioritised findings list below. Include file paths and line numbers. Omit tiers with no findings.

Output Format

## Background Execution Audit — Findings

### 🔴 CRITICAL — Guaranteed rejection
- [ ] TODO: Remove silent audio background mode — playing inaudible audio to prevent suspension violates 2.5.4; use BGTaskScheduler for background work — `AudioKeepAlive.swift:12` — Guideline 2.5.4
- [ ] TODO: Remove voip background mode or integrate CallKit — voip mode requires telephone-like calling functionality via CXProvider — `Info.plist` — Guideline 2.5.4

### 🟠 HIGH — Very likely rejection
- [ ] TODO: Replace CoreLocation-based step counting with CMPedometer — background location is not required for pedometry — `StepTracker.swift:34` — Guideline 2.5.4
- [ ] TODO: Register BGProcessingTask in BGTaskScheduler — background-processing mode declared but BGTaskScheduler not configured — `AppDelegate.swift` — Guideline 2.5.4

### 🟡 MEDIUM — Possible rejection
- [ ] TODO: Review all declared UIBackgroundModes against actual usage — remove any mode not actively used by a core feature

### 🟢 LOW — Best practice
- [ ] TODO: Add a comment next to each UIBackgroundMode entry explaining which feature requires it — helps reviewers and future maintainers understand the justification

Tools Used

Glob, Grep, Read

Constraints

• Read-only. No file edits.
• No network calls.
• Skip Phase 1 if shared_context is provided by orchestrating agent.
• Legitimate uses of background modes (music players for audio, navigation apps for location, calling apps for voip) are not flagged — context from Phase 2 checks determines whether usage matches intent.

Quick Commands

# Check declared background modes
!plutil -convert json -o - Info.plist 2>/dev/null | python3 -c "import sys,json; d=json.load(sys.stdin); print('Background modes:', d.get('UIBackgroundModes', 'none'))"

# Check for silent audio pattern
!grep -rn "AVAudioSession\|AVAudioPlayer" . --include="*.swift" -A5 | grep -i "ambient\|volume.*0\|setVolume(0"

# Check for BGTaskScheduler usage
!grep -rn "BGTaskScheduler\|BGProcessingTask\|BGAppRefreshTask" . --include="*.swift"

# Check for voip + CallKit
!grep -rn "CXProvider\|CXCallController\|CallKit" . --include="*.swift" | wc -l

Swift Anti-Pattern Reference

examples/swift/BackgroundExecutionPatterns.swift

Detection Steps

1. Find target files

   • Glob: **/Info.plist, **/*.swift, **/*.m

2. Search for rejection patterns

   • Read Info.plist → check UIBackgroundModes array values
   • Grep AVAudioSession.*categoryPlayback\|AVAudioSession.*setCategory.*playback + mixWithOthers — silent audio abuse
   • Grep kCLAuthorizationStatusAuthorizedAlways\|requestAlwaysAuthorization — always location
   • Grep PKPushRegistry\|voip in Info.plist UIBackgroundModes — VoIP background mode
   • Grep CXProvider\|CXCallController — CallKit usage (required for VoIP)

3. Determine verdict

   • audio in UIBackgroundModes + mixWithOthers option (silent audio trick) → 🔴 CRITICAL (Guideline 2.5.4)
   • location in UIBackgroundModes + app is not navigation/fitness → 🔴 CRITICAL
   • voip in UIBackgroundModes + no CXProvider (CallKit) usage → 🔴 CRITICAL
   • Background modes match actual app functionality → 🟢 pass

4. Report

   • UIBackgroundModes values found in Info.plist
   • File path + line of silent audio / location / VoIP misuse
   • Fix: Remove background modes that don't match core app features; implement CallKit for VoIP