The decision model

For a state, DefaultNexusEngine::evaluate() resolves a NexusStatus in this precedence:

1. Registered — the seller already holds a registration there (obligation handled).
2. Triggered (physical) — asserted physical presence establishes nexus on its own, whatever the sales.
3. Triggered (economic) — cumulative activity crosses the threshold (combinator-aware: sales-only, sales-or-transactions, sales-and-transactions).
4. Approaching — activity is within the configured band (default 80%) of the threshold. A watch signal, not an obligation.
5. Below — under the band, or no threshold/activity is known.

Only Triggered returns needsAction() === true. Each NexusEvaluation also carries the threshold, activity, a progress ratio (0–1+ toward crossing), physicalPresence, and a human-readable reason.

A NexusReport buckets a set of evaluations into triggered(), approaching() and registered() for a platform dashboard.