Example 01 — Invoice Extraction (lease)

Phase 5 case study demonstrating the lease transfer mode (PROTOCOL_SPEC.md §6.2).

Story

• CompanyA Finance Agent needs to process a Q3 close batch of 50 invoices.
• CompanyB Document Agent publishes an extract-invoice skill at $0.05/invocation, supports lease for up to 1000 invocations / 24 h, and signs agreements with Ed25519.
• A lease saves CompanyA the negotiation overhead per call: one signed agreement covers the whole batch.

Run

uv run python -m examples.01_invoice_extraction.main

What it demonstrates

1. Discovery — fetching the Agent Card and the manifest.
2. Negotiation — counter-offer on price ($0.05 published → $0.04 in agreement); lease parameters set to the batch size.
3. Signed agreement — provider signs with Ed25519; client resolves the provider’s did:web DID document and verifies before honoring.
4. Lease invocations — 50 successful calls, with invocation counter visible.
5. Lease enforcement — the 51st call is rejected with AgreementViolatedError (-32003 Agreement violated), proving the budget is enforced server-side.

Where this maps to the spec

Spec section	Demonstrated by
§3 Manifest	build_invoice_manifest()
§5 Negotiation FSM	propose → accept flow
§5.3 Agreement	signed agreement printed in step 2
§6.2 lease	invocation budget enforced in step 5
§7 Identity (Phase 4)	step 3 verifies the provider’s JWS via did:web