Lovable-friendly entry point: same x402 quote → pay → call loop as `pay_then_call`, plus vertical-aware pricing. Pass `vertical` (logistics, legal, oracles, banking, fintech, healthcare, insurance, government, defense, …) and the upstream x402 server re-prices each accepts[] entry by tier (standard 1× / regulated 1.5× / sovereign 2.5× / defense 3×). Pass `attestation: "pio:<id>"` (or fedramp:/soc2:) for a 20% compliance discount on regulated+ tiers. The signed receipt envelope is tagged `source: "lovable"` and includes a `vertical: { claimed_slug, attestation, quoted: { tier, multiplier, attested, ... } }` block recording the tier the upstream actually quoted — that is the audit trail for tier billing. Returns { paid, upstream_status, response, signed_context: { envelope, envelope_json, envelope_sha256, signature, signer, scheme: 'EIP-191' } }. Pass `idempotency_key` to safely retry without double-settling.