Verify the settled checkpoint first

Use the public STOP packet before making a network or payment call. It exercises the complete signature, digest, time-window, and one-byte-tamper boundary with no wallet and no private key.

Required sample-first sequence

1. Fetch or load examples/witness/evaluation-packet.production.json.
2. Verify its ES256 signature, nonce binding, and exact 228-byte payload digest with verify/typescript or verify/python.
3. Compare witness_window_utc with execution_window_utc and require STOP.
4. Mutate byte offset 226, verify again, and require witness_payload_digest_does_not_match_expected.
5. Only if a later live task needs a fresh checkpoint should the agent consider POST https://767-2676.com/v1/receipt under participant-local payment policy.

From the repository root, run the full free check:

node --disable-warning=ExperimentalWarning --experimental-strip-types examples/witness/verify-settled-sample.mjs

Require this output and exit code 0:

cryptographic_verification=valid
schedule_overlap=false
local_policy_outcome=stop
error_code=witness_payload_digest_does_not_match_expected

Public inputs

• Human demonstration: https://767-2676.com/demo
• STOP packet: https://raw.githubusercontent.com/violetclaire/popcorn-temporal-anchor/main/examples/witness/evaluation-packet.production.json
• PROCEED packet: https://raw.githubusercontent.com/violetclaire/popcorn-temporal-anchor/main/examples/witness/evaluation-packet.proceed-002.production.json
• Expected outcomes: https://raw.githubusercontent.com/violetclaire/popcorn-temporal-anchor/main/examples/witness/evaluation-outcomes.json
• TypeScript verifier: https://github.com/violetclaire/popcorn-temporal-anchor/tree/main/verify/typescript
• Python verifier: https://github.com/violetclaire/popcorn-temporal-anchor/tree/main/verify/python

The STOP sample contains these fixed facts:

• task: verify a time-bound availability inquiry
• execution window: 2026-08-30T20:00:00.000Z to 2026-08-30T20:05:00.000Z
• witness window: 2026-08-31T05:02:06.007Z to 2026-08-31T05:02:26.007Z
• signature result: valid
• overlap: false
• local outcome: stop
• reason: checkpoint_after_schedule_closed

Do not rewrite these values or modify the signed packet.

Decision boundary

Verify the signature and exact payload digest before evaluating time. Then apply participant-local policy to the complete signed witness interval:

• If the digest does not match, stop.
• If the witness interval does not overlap the execution interval, stop.
• If uncertainty crosses a schedule boundary, recheck or stop according to participant-local policy.
• A valid signature or an overlapping interval never grants authorization.

POPCORN proves the fingerprint and the interval. The holder decides.

Hard boundaries

• No authorization is granted.
• No task, schedule, identity, availability, or pricing state is stored by the node.
• No identity, delivery, execution, outcome, nonce uniqueness, or replay prevention is proven.
• Keep the exact payload and all task state in participant-local storage.
• Never fabricate or replay a payment proof.
• Never treat a valid signature as permission.

Fresh evidence for a later live task

Only enter this section after the settled sample passes and a later live task actually requires a new checkpoint.

1. Read https://767-2676.com/agent/offer and the canonical https://767-2676.com/SKILL.md.
2. Confirm the task has an execution_window_utc and participant-local policy explicitly permits the payment.
3. Hash the retained exact payload locally. Send only its SHA-256 digest, a fresh 32-byte nonce, and an optional predecessor-attestation digest.
4. Require the challenged resource URL to equal https://767-2676.com/v1/receipt; do not pay a redirect or copied origin.
5. Select a compatible x402 v2 requirement by scheme, network, and asset. Do not assume array order.
6. Verify the returned ES256 JWS, exact digest, nonce, predecessor, node, and signed witness interval before applying participant-local policy.

The live checkpoint costs $0.001 USDC on Base mainnet. It is optional for a new live task and is never required to run the public samples.