axiom-camera-capture-diag

# Camera Capture Diagnostics

Systematic troubleshooting for AVFoundation camera issues: frozen preview, wrong rotation, slow capture, session interruptions, and permission problems.

## Overview

**Core Principle**: When camera doesn't work, the problem is usually:
1. **Threading** (session work on main thread) - 35%
2. **Session lifecycle** (not started, interrupted, not configured) - 25%
3. **Rotation** (deprecated APIs, missing coordinator) - 20%
4. **Permissions** (denied, not requested) - 15%
5. **Configuration** (wrong preset, missing input/output) - 5%

**Always check threading and session state BEFORE debugging capture logic.**

## Red Flags

Symptoms that indicate camera-specific issues:

| Symptom | Likely Cause |
|---------|--------------|
| Preview shows black screen | Session not started, permission denied, no camera input |
| UI freezes when opening camera | `startRunning()` called on main thread |
| Camera freezes on phone call | No interruption handling |
| Preview rotated 90° wrong | Not using RotationCoordinator (iOS 17+) |
| Captured photo rotated wrong | Rotation angle not applied to output connection |
| Front camera photo not mirrored | This is correct! (preview mirrors, photo does not) |
| "Camera in use by another app" | Another app has exclusive access |
| Capture takes 2+ seconds | `photoQualityPrioritization` set to `.quality` |
| Session won't start on iPad | Split View - camera unavailable |
| Crash on older iOS | Using iOS 17+ APIs without availability check |

## Mandatory First Steps

Before investigating code, run these diagnostics:

### Step 1: Check Session State

```swift
print("📷 Session state:")
print("  isRunning: \(session.isRunning)")
print("  inputs: \(session.inputs.count)")
print("  outputs: \(session.outputs.count)")

for input in session.inputs {
    if let deviceInput = input as? AVCaptureDeviceInput {
        print("  Input: \(deviceInput.device.localizedName)")
    }
}

for output in session.outputs {
    print("  O