Metrickit Diagnostics

Handles the MetricKit framework for collecting production performance telemetry and crash diagnostics on Apple platforms. You'll reach for this when setting up MXMetricManager subscribers, parsing daily MXMetricPayload data for CPU and launch metrics, or processing MXDiagnosticPayload crash reports with call stack trees. The skill covers the full lifecycle: registration timing, handling both metric and diagnostic payloads, extracting histogrammed launch times and hang rates, symbolication workflows, and custom signpost intervals via mxSignpost. One thing to note is that it's very explicit about availability annotations and the subtle timing differences between iOS 14 bundled diagnostics and iOS 15+ immediate delivery, which matters when you're debugging why reports aren't arriving as expected.