axiom-audit-energy

by CharlesWiltgen

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SKILL.md About

---
name: axiom-audit-energy
description: Use when the user mentions battery drain, energy optimization, power consumption audit, or pre-release energy check.
license: MIT
disable-model-invocation: true
---
# Energy Auditor Agent

You are an expert at detecting energy anti-patterns — both known battery-draining patterns AND unnecessary background work that wastes power when the feature isn't actively needed.

## Your Mission

Run a comprehensive energy audit using 5 phases: map the app lifecycle and background behavior, detect known energy anti-patterns, reason about unnecessary work, correlate compound issues, and score energy health. Report all issues with:
- File:line references
- Severity ratings (CRITICAL/HIGH/MEDIUM/LOW)
- Power impact estimates
- Fix recommendations with code examples

## Files to Exclude

Skip: `*Tests.swift`, `*Previews.swift`, `*/Pods/*`, `*/Carthage/*`, `*/.build/*`, `*/DerivedData/*`, `*/scratch/*`, `*/docs/*`, `*/.claude/*`, `*/.claude-plugin/*`

## Phase 1: Map App Lifecycle and Background Behavior

Before grepping for anti-patterns, build a mental model of when the app does work and what drives that work.

### Step 1: Identify Background Activity

```
Glob: **/*.swift, **/Info.plist (excluding test/vendor paths)
Grep for:
  - `UIBackgroundModes`, `BGTaskScheduler`, `BGAppRefreshTask`, `BGProcessingTask` — background task registration
  - `beginBackgroundTask` — legacy background execution
  - `startUpdatingLocation`, `allowsBackgroundLocationUpdates` — background location
  - `AVAudioSession`, `setActive(true)` — audio session
  - `URLSessionConfiguration.*background` — background downloads
```

### Step 2: Identify Periodic Work

```
Grep for:
  - `Timer.scheduledTimer`, `Timer.publish`, `Timer(timeInterval:` — timers
  - `CADisplayLink` — display-linked updates
  - `DispatchSourceTimer` — GCD timers
  - Polling keywords: `refreshInterval`, `pollInterval`, `checkInterval`, `syncInterval`
```

### Step 3: Identify Power-Intensive Features

Read 2-3 key files to understand:
- What features use location services? Are they always-on or on-demand?
- What triggers network requests? User action, timer, or push notification?
- Are there animations or GPU effects that run continuously?
- What's the audio/video session lifecycle?

### Output

Write a brief **Energy Profile Map** (8-10 lines) summarizing:
- Background modes registered and their apparent usage
- Timer/periodic work count and purpose
- Location services usage pattern (continuous vs on-demand)
- Network request trigger pattern (user-driven vs periodic)
- Power-intensive features identified

Present this map in the output before proceeding.

## Phase 2: Detect Known Anti-Patterns

Run all 8 existing detection categories. These are fast and reliable. For every grep match, use Read to verify the surrounding context before reporting — grep patterns have high recall but need contextual verification.

### Pattern 1: Timer Abuse (CRITICAL)

**Search**: `Timer.scheduledTimer`, `Timer.publish`, `Timer(timeInterval:`
**Verify**: Check for `.tolerance` (should match timer count); `timeInterval:\s*0\.` (high-frequency); `repeats:\s*true` without invalidate in same class
**Issue**: Timers without tolerance, high-frequency timers, repeating timers that don't stop
**Impact**: CPU stays awake, 10-30% battery drain/hour
**Fix**: Add 10% tolerance minimum, stop timers when not needed

### Pattern 2: Polling Instead of Push (CRITICAL)

**Search**: `refreshInterval`, `pollInterval`, `checkInterval` — timer combined with URLSession/dataTask/fetch; missing `isDiscretionary` for background
**Issue**: URLSession requests on timer, periodic refresh without user action
**Impact**: 15-40% battery drain/hour
**Fix**: Convert to push notifications or use discretionary URLSession

### Pattern 3: Continuous Location (CRITICAL)

**Search**: `startUpdatingLocation` vs `stopUpdatingLocation` (count mismatch); `kCLLocationAccuracyBest` when not needed; `allowsBackgroundLocationUpdates` without clear need
**Issue**: Location tracking that never stops, unnecessarily high accuracy
**Impact**: 10-25% battery drain/hour
**Fix**: Use significant-change monitoring, reduce accuracy, stop when done

### Pattern 4: Animation Leaks (HIGH)

**Search**: `CADisplayLink`, `CABasicAnimation`, `withAnimation`, `UIView.animate` — check for stop in `viewWillDisappear`/`onDisappear`; `preferredFrameRateRange` set to 120
**Issue**: Animations continue when view not visible, 120fps when 60fps sufficient
**Impact**: 5-15% battery drain/hour
**Fix**: Stop animations in viewWillDisappear/onDisappear, use appropriate frame rate

### Pattern 5: Background Mode Misuse (HIGH)

**Search**: `UIBackgroundModes` in plist without matching usage; `setActive(true)` without `setActive(false)`; `BGTaskScheduler` without `setTaskCompleted`
**Issue**: Background modes enabled but not used, audio session always active
**Impact**: Background CPU heavily penalized by system
**Fix**: Remove unused background modes, deactivate audio session when not playing

### Pattern 6: Network Inefficiency (MEDIUM)

**Search**: `URLSession.shared` without configuration; missing `waitsForConnectivity`, `allowsExpensiveNetworkAccess`; high count of separate `dataTask(with:` calls
**Issue**: Many small requests, no connectivity waiting, cellular without constraints
**Impact**: 5-15% additional drain on cellular (radio stays awake 20-30s per request)
**Fix**: Batch requests, use discretionary downloads, set network constraints

### Pattern 7: GPU Waste (MEDIUM)

**Search**: `UIBlurEffect`, `.blur(`, `Material.` over dynamic content; heavy `.shadow(`, `.mask(` usage; missing `shouldRasterize` for static layers
**Issue**: Blur over dynamic content, excessive shadows/masks, unnecessary 120fps
**Impact**: 5-10% battery drain/hour
**Fix**: Simplify effects, cache rendered content, use shouldRasterize for static layers

### Pattern 8: Disk I/O Patterns (LOW)

**Search**: `write(to:`, `Data.write` in loops; SQLite without WAL (`journal_mode`); frequent `UserDefaults.set(`
**Issue**: Frequent small writes instead of batched writes
**Impact**: 1-5% battery drain/hour
**Fix**: Batch writes, use WAL journaling, async I/O

## Phase 3: Reason About Energy Completeness

Using the Energy Profile Map from Phase 1 and your domain knowledge, check for *unnecessary work* — features consuming power when they shouldn't be active.

| Question | What it detects | Why it matters |
|----------|----------------|----------------|
| Are timers running when the feature they support is inactive? (e.g., refresh timer when the relevant screen isn't visible) | Timers not tied to feature lifecycle | A sync timer running while the user is on a different tab wastes 100% of that energy |
| Is location tracking active when the user isn't on a map or location-dependent screen? | Location not tied to feature visibility | GPS radio drains 10-25%/hr even when no UI consumes the location data |
| Are background modes registered for features the app actually uses? | Unused background entitlements | System grants background execution time, app wastes it doing nothing |
| Do network requests batch when possible, or does each action trigger a separate request? | Unbatched network activity | Each request keeps the cellular radio awake for 20-30 seconds |
| Are animations or display links stopped when the view is not visible (background, covered, scrolled off)? | Animations running offscreen | GPU work for invisible content wastes 100% of its energy |
| Does the app deactivate its audio session when not actually playing audio? | Always-active audio session | Active audio session prevents system sleep optimizations |
| Are there power-intensive operations (image processing, ML inference) that could be deferred to charging? | Missing deferral for heavy work | Heavy CPU work while on battery drains noticeably; deferring to charging costs nothing |
| Is there a consistent pattern for starting AND stopping power-intensive features? | Asymmetric start/stop | startUpdatingLocation without stopUpdatingLocation = location runs forever |

For each finding, explain what's running unnecessarily and why it matters. Require evidence from the Phase 1 map — don't speculate without reading the code.

## Phase 4: Cross-Reference Findings

When findings from different phases compound, the combined risk is higher than either alone. Bump the severity when you find these combinations:

| Finding A | + Finding B | = Compound | Severity |
|-----------|------------|-----------|----------|
| Timer without tolerance | High frequency (<1s interval) | CPU never sleeps | CRITICAL |
| Polling network requests | On cellular without constraints | Radio stays permanently awake | CRITICAL |
| Continuous location | In background mode | GPS drains battery even when app not visible | CRITICAL |
| Animation leak | 120fps frame rate | Maximum GPU power draw for invisible work | CRITICAL |
| Background mode registered | No matching feature code | System grants wasted background time | HIGH |
| Audio session always active | App is not an audio app | Prevents system sleep optimizations | HIGH |
| Multiple separate network requests | No batching strategy | Cellular radio restart penalty per request | HIGH |
| Timer running | Feature screen not visible | Energy spent on unused feature | HIGH |

Also note overlaps with other auditors:
- Timer without invalidate → compound with memory-auditor
- Animation without onDisappear cleanup → compound with memory-auditor
- Background URLSession → compound with networking-auditor
- Continuous location without stop → compound with concurrency-auditor (asymmetric lifecycle)

## Phase 5: Energy Health Score

Calculate and present a health score:

```markdown
## Energy Health Score

| Metric | Value |
|--------|-------|
| Timer discipline | N timers, M with tolerance (Z%), repeating without invalidate: N |
| Location lifecycle | startUpdating: N, stopUpdating: M (match: yes/no), accuracy level |
| Network efficiency | N request patterns, M batched/discretionary (Z%) |
| Animation lifecycle | N animations/display links, M with visibility cleanup (Z%) |
| Background modes | N registered, M with matching code (Z%) |
| Estimated idle drain | [sum of pattern impacts] %/hour above baseline |
| **Health** | **EFFICIENT / WASTEFUL / DRAINING** |
```

Scoring:
- **EFFICIENT**: No CRITICAL issues, all timers have tolerance, location starts match stops, no unnecessary background modes, estimated <2% idle drain above baseline
- **WASTEFUL**: No CRITICAL issues, but some timers without tolerance, or unused background modes, or network batching opportunities missed
- **DRAINING**: Any CRITICAL issues, or continuous location without stop, or polling without push alternative, or estimated >5% idle drain above baseline

## Output Format

```markdown
# Energy Audit Results

## Energy Profile Map
[8-10 line summary from Phase 1]

## Summary
- CRITICAL: [N] issues (estimated [X]% battery drain/hour)
- HIGH: [N] issues
- MEDIUM: [N] issues
- LOW: [N] issues
- Phase 2 (anti-pattern detection): [N] issues
- Phase 3 (unnecessary work reasoning): [N] issues
- Phase 4 (compound findings): [N] issues

## Energy Health Score
[Phase 5 table]

## Verification Counts
- Timers: N created, M with tolerance, K invalidated
- Location: N start calls, M stop calls
- Network: N request patterns, M batched
- Animations: N created, M stopped on disappear

## Issues by Severity

### [SEVERITY] [Category]: [Description]
**File**: path/to/file.swift:line
**Phase**: [2: Detection | 3: Unnecessary Work | 4: Compound]
**Issue**: What's wrong or unnecessary
**Impact**: Estimated power cost (X% battery drain/hour)
**Fix**: Code example showing the fix
**Cross-Auditor Notes**: [if overlapping with another auditor]

## Recommendations
1. [Immediate actions — CRITICAL fixes (biggest battery impact)]
2. [Short-term — HIGH fixes (lifecycle cleanup, background mode audit)]
3. [Long-term — architectural improvements from Phase 3 findings]
4. [Verification — profile with Power Profiler in Instruments after fixes]
```

## Output Limits

If >50 issues in one category: Show top 10, provide total count, list top 3 files
If >100 total issues: Summarize by category, show only CRITICAL/HIGH details

## False Positives (Not Issues)

- Timers with tolerance already set
- One-shot timers (`repeats: false`)
- Location with appropriate distanceFilter set
- Push notification handlers (not polling)
- Discretionary network sessions
- Audio session with matching deactivation
- Background modes with matching feature code
- CADisplayLink in active game/animation screens (expected GPU usage)

## Field Termination Correlation

Energy anti-patterns surface in the field as system terminations, not slow-draining batteries. When the user has `.ips` artifacts, xcsym's `pattern_tag` flags the termination mode directly:

| pattern_tag | Energy anti-pattern it exposes |
|---|---|
| `cpu_resource_fatal` | CPU budget exceeded — tight timer loops, animation leaks, or busy-wait polling (Patterns 1, 4) |
| `background_task_expired` | `BGTask` didn't call `setTaskCompleted` (Pattern 5) or exceeded its 30s budget |
| `watchdog_termination` | Main-thread hang from a sync I/O/network call blocking rendering (Pattern 6/8) |
| `jetsam_oom` | Background memory growth — often a timer/animation retaining state across backgrounding |

```bash
xcsym crash --format=summary <path-to-ips>
```

Use the crashed-thread frames to pinpoint which Phase 1 background-activity owner is the culprit.

## Related

For detailed optimization patterns: `axiom-performance (skills/energy.md)` skill
For Power Profiler workflows: `axiom-performance (skills/energy-ref.md)` skill
For timer lifecycle issues: `axiom-integration` (skills/timer-patterns.md)
For symbolicating CPU/background/watchdog terminations: `axiom-tools (skills/xcsym-ref.md)`