Check signed receipts on x402 Doctor and presign-guard answers (0.9.0)

[Fizzl13]

x402 Doctor and presign-guard now sign every paid answer: EIP-191 over canonical JSON, with the request inside the signed body. The actions that decide "pay" or "sign" now check it, so an agent never acts on a verdict that isn't provably from the service, for exactly its request.

What

• FIZZL_PREFLIGHT_X402, FIZZL_DIAGNOSE_X402 and FIZZL_PRESIGN_CHECK verify the receipt:
  • signed by the service's pinned signer: Doctor 0xAaE6…277d, presign-guard 0xf084…1EaE;
  • its input_sha256 matches the request that was sent: the query for Doctor, the JSON body for presign-guard.
• A valid answer ends with "Signed by x402 Doctor ✓ (receipt …)".
• A changed, unsigned or foreign answer, or one for another request, is not used: the action fails with "Do not pay on it" or "Do not sign until it can be checked".
• src/receipt.ts: canonical JSON, input hash, verifyReceipt (viem, already a dependency) and SIGNERS.
• The services attach the signed request (route and input) to each result.
• New settings: FIZZL_VERIFY_RECEIPTS (require by default, or off), FIZZL_DOCTOR_SIGNERS and FIZZL_PRESIGN_SIGNERS.
• README "Signed verdicts" section; version 0.9.0.

Tests

• The fixtures now sign like the live services, so every existing Doctor and presign test runs through the check.
• New cases: a flipped verdict, a missing receipt, a foreign signer and the off switch.
• The pinned signers are checked.
• Real production receipts from both services verify, and fail when changed or checked against the other service's key.
• npm test: 40/40.

After merge

Publish 0.9.0 (the Publish to npm workflow).

🤖 Generated with Claude Code

https://claude.ai/code/session_01TsD5haPKxeWjYmErHzvU48

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