Go runner

Register typed handlers and run a capacity-aware worker.

registry := headgate.NewRegistry()
err := headgate.RegisterFunc[GenerateInvoice](registry,
    func(ctx context.Context, job *headgate.Job[GenerateInvoice]) error {
        headgate.Log(ctx, "generating "+job.Args.InvoiceID)
        return nil
    })
if err != nil { return err }

runner := headgate.NewRunner(store, registry, headgate.Config{
    Queues: map[string]headgate.QueueConfig{
        "billing": {MaxWorkers: 16},
    },
})
return runner.Run(ctx)

Cancel the context during normal process shutdown. The runner stops admission and performs a bounded graceful drain while preserving leases.