Converts one testEnd into a JUnit <testcase>. Failing assertions are flattened into a failureDetail with stacks resolved back to original sources (same as the TAP at: field).

import type { ReporterContext } from './types.ts';

toCase({} as ReporterContext, { status: 'passed', fullName: ['Math', 'adds'], runtime: 1500 });
// { classname: 'Math', name: 'adds', time: 1.5, status: 'passed' } — context is only
// read for failed tests (the group's source-map decoder resolves their stacks)