feat(receipt): show what the signature actually binds, and stop dropping the amount

[dkitchell]

The demo artifact carries the whole story and the tool was showing none of it.

Before

✓ VALID  receipt 2492a060-8fbc-40ae-beab-7258aefb0608
  signed by    (published Agent Commerce key) (CertifiedData.io)
  signature    pass
  payload hash pass
  public key   /.well-known/certifieddata-public-key.pem
  settlement   succeeded_live

After

✓ VALID  receipt 2492a060-8fbc-40ae-beab-7258aefb0608
  signed by    (published Agent Commerce key) (CertifiedData.io)
  signature    pass
  payload hash pass
  public key   /.well-known/certifieddata-public-key.pem

  ── bound by this signature ──
  amount         0.99 USD
  settlement     succeeded_live
  settled at     2026-08-20T22:39:38.008Z
  rail           stripe
  purpose        Dataset purchase: fraud-detection-verification-sample (certificate-linked, 500 rows x 7 columns)
  agent          38ed5be8-fb59-438e-b99d-73549b242b09
  policy         0acaeed1-7dbc-4c17-b405-c31517a0be78
  policy hash    sha256:f4e59785c1f3107b3f6afac362051fe42bc25d3605ee641e8936f0e8c3a1eb8d
  authorization  df033885-5b76-4137-8aa4-a8e8a98a95b2
  decision       709519fd-40bb-445e-a6c4-b9b2b1cba9fb
  artifact hash  sha256:bd48985485c9a3e19838e29795bb89ddedd7f7e5c706b57c190cc6c46119a660
  certificate    fb914a90-b1b3-4355-8147-cc0194160e23
  transaction    b00d1924-6187-49f3-aee7-3bbffff1c78c
  payment ref    pi_3U6ecXDRYQxqHzlc2IoF5mAB

  The verdict above was computed locally — not taken from the server.

That is real output from the live production receipt, not a mockup.

Why this is the right failure to fix

The pitch is "don't trust our dashboard, verify it yourself." The verifier was answering with an unsupported VALID and leaving the substance — which policy, which artifact, which decision, which settlement — to be taken on trust anyway. The signature was only as interesting as what it bound, and the tool never said.

Safety: everything printed is read from the payload that has already passed both the signature and payload-hash checks, so nothing is displayed as bound by a signature that does not cover it. A post-signing tamper fails before any of it renders. Absent fields are omitted rather than invented.

A silent data bug found while wiring this up

Production emits amount as a string ("99"). The code tested typeof p.amount === "number", so every real receipt verified with no amount displayed at all. Both forms now work; a non-numeric value is dropped rather than coerced into something wrong.

Verified against production

Each binding was confirmed to dereference before being surfaced:

link	state
certificate fb914a90…	ISSUED — retained, not one of the #383 orphans
…in transparency log	log_index 689
decision record 709519fd…	exists, written 21s before the receipt
authorization df033885…	executed

Tests

98, up from 93. New coverage: the binding surface, both amount forms, non-numeric amounts, absent bindings reported as null rather than invented, and that a post-signing tamper fails before anything is reported as bound.

Version bumped to 0.1.1.

🤖 Generated with Claude Code