describe-ui returns empty hierarchy on iOS 26+ simulators — auto-enable accessibility defaults

[dpearson2699]

Problem

On iOS 26 / Xcode 26.x, new simulator devices ship with AccessibilityEnabled = 0 and ApplicationAccessibilityEnabled = 0 in com.apple.Accessibility preferences. This causes axe describe-ui to return only a bare AXApplication node with empty children: [] and a zero-size frame {{0, 0}, {0, 0}}.

This affects all apps including Apple's own Settings.app — it's not an app-side issue.

Root cause

$ xcrun simctl spawn <UDID> defaults read com.apple.Accessibility
{
    AccessibilityEnabled = 0;
    ApplicationAccessibilityEnabled = 0;
    ...
}

With these flags off, the accessibility daemon doesn't expose any element tree. FBSimulatorControl's XPC queries return the empty Application node.

Workaround

xcrun simctl spawn <UDID> defaults write com.apple.Accessibility AccessibilityEnabled -bool true
xcrun simctl spawn <UDID> defaults write com.apple.Accessibility ApplicationAccessibilityEnabled -bool true

After this, describe-ui immediately returns the full hierarchy. The setting persists in the device's preferences plist until "Erase All Content and Settings" or device deletion.

Suggested fix

axe could auto-enable these when it detects an empty hierarchy:

1. After describe-ui gets a result with zero children, check com.apple.Accessibility defaults on the target sim
2. If either flag is 0, enable both and retry
3. Log a note so users know it was auto-fixed

This would make snapshot-ui work out of the box on fresh iOS 26 simulators. Currently there's nothing telling users why the tree is empty — the output just looks like the app has no UI.

Environment

• macOS 26.3.1, Xcode 26.3, iOS 26.2 runtime
• XcodeBuildMCP 2.3.0, axe v1.5.2