Data seams

Rebind any contract in a service provider. The three host seams are empty by default (deny-by-default).

SalesLedger (required for economic nexus)

Your cumulative sales/transactions into each state, over the state's measuring period. This is the seller's side of the equation — the package cannot know it.

use Cbox\Nexus\Contracts\SalesLedger;
use Cbox\Nexus\ValueObjects\ActivityQuery;
use Cbox\Nexus\ValueObjects\SellerActivity;

app()->singleton(SalesLedger::class, fn () => new class implements SalesLedger {
    public function activityFor(ActivityQuery $query): ?SellerActivity { /* from invoices */ }
});

The query carries the state's own terms — basis, period, and windows() giving the concrete dates — so the sum can be run without looking the state's rules up separately.

Serving more than one seller

$query->subject names who the question is about. It is null when the host serves a single seller, which is the common case and needs nothing.

If you serve several and the subject is null, return null; the engine reports that as Unknown. Do not fall back on the current request or a container-scoped singleton. A queued job or a long-lived worker carries whoever was served last, so that fallback returns one seller's totals for another seller's state — silently, and across a tenant boundary. PhysicalNexus and NexusRegistrations take the same subject under the same rule; of the three a wrongly-claimed registration is the worst, because it turns an outstanding obligation into a handled one on a dashboard.

PhysicalNexus

States where the seller has an office, employees or inventory (e.g. FBA) — a nexus trigger on its own. Host-asserted.

NexusRegistrations

States the seller already holds a registration in, so a handled obligation reports as Registered rather than an outstanding action.

NexusThresholdSource

Defaults to the us-tax-data dataset. Rebind it to pin a different dataset copy or supply thresholds from elsewhere; a state it doesn't carry returns null (deny-by-default).