axiom-swiftui-debugging-diag

# SwiftUI Debugging Diagnostics

## When to Use This Diagnostic Skill

Use this skill when:
- **Basic troubleshooting failed** — Applied `axiom-swiftui-debugging` skill patterns but issue persists
- **Self._printChanges() shows unexpected patterns** — View updating when it shouldn't, or not updating when it should
- **Intermittent issues** — Works sometimes, fails other times ("heisenbug")
- **Complex dependency chains** — Need to trace data flow through multiple views/models
- **Performance investigation** — Views updating too often or taking too long
- **Preview mysteries** — Crashes or failures that aren't immediately obvious

## FORBIDDEN Actions

Under pressure, you'll be tempted to shortcuts that hide problems instead of diagnosing them. **NEVER do these**:

❌ **Guessing with random @State/@Observable changes**
- "Let me try adding @Observable here and see if it works"
- "Maybe if I change this to @StateObject it'll fix it"

❌ **Adding .id(UUID()) to force updates**
- Creates new view identity every render
- Destroys state preservation
- Masks root cause

❌ **Using ObservableObject when @Observable would work** (iOS 17+)
- Adds unnecessary complexity
- Miss out on automatic dependency tracking

❌ **Ignoring intermittent issues** ("works sometimes")
- "I'll just merge and hope it doesn't happen in production"
- Intermittent = systematic bug, not randomness

❌ **Shipping without understanding**
- "The fix works, I don't know why"
- Production is too expensive for trial-and-error

## Mandatory First Steps

Before diving into diagnostic patterns, establish baseline environment:

```bash
# 1. Verify Instruments setup
xcodebuild -version  # Must be Xcode 26+ for SwiftUI Instrument

# 2. Build in Release mode for profiling
xcodebuild build -scheme YourScheme -configuration Release

# 3. Clear derived data if investigating preview issues
rm -rf ~/Library/Developer/Xcode/DerivedData
```

**Time cost**: 5 minutes
**Why**: Wrong Xcode version or Debug mode produces misle