This is a live invoice model with real business rules. Edit any field and the verdict updates instantly — the same deterministic logic that runs in the browser and, in production, on the server where it can't be bypassed. Switch rule versions on the right to see how the model evolved. Nothing you type leaves your browser.
Ledger already holds invoices INV-1001 and INV-1002 — reuse one to trip the duplicate guard.
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Every rule change is a signed version. Click one to run the model as it was then.
The rules aren't sprinkled through the UI. They derive from the invoice's schema — the entities and constraints — so the form, the API, and the verdict all read the same source of truth.
The exact logic you're running here runs again server-side, where it can't be bypassed. Same input, same verdict, every time — no model call, no randomness, no per-token bill.
Every change to the rules is a new, content-addressed version in the history — auditable and reversible. Nothing shifts silently; you can always run exactly the model that made a past decision.