Builds the merged qunitx config from package.json settings and either an argv or an explicit ConfigOptions. package.json#qunitx.plugins entries are dynamic-imported into esbuild plugin objects.

ConfigFailure is declared, so .result() hands back the bare union to branch on with Failure.is. It reports rather than exits so the daemon — which assembles a config per client request — can reject one bad flag and stay up; cli.ts turns a failure into an exit.

Lazy, like every Task: nothing is read until it is awaited. With no argument setup reads process.argv and process.env at that moment, so a caller that lends those globals (the daemon, via borrowArgv/borrowEnv) must await INSIDE the borrowing scope, not hold the Task past it. Passing options instead skips the argv read entirely — which is why the JS API needs no such borrowing.

import * as Config from './config.ts';
import * as Result from '../result/index.ts';

// Defined, not invoked: reads package.json and walks the real fs.
async function example() {
  const config = await Config.setup({ inputs: ['test/'] }).result();
  return Result.Failure.is(config) ? config.code : config.inputs; // ConfigFailure, or the Config
}