ONE INDEPENDENT OUTSIDE SPONSOR · PUBLIC SOURCE + NANO MAINNET EVIDENCE
A real engineering fix. A real external 5 XNO reward.
We contributed a fail-closed concurrent wallet-lock repair to an independently maintained open-source x402 Nano payment client. The outside maintainer ran the tests, merged the pull request and announced payment. This is a completed, independently reviewed engineering delivery—not a claim that unrelated PaperPilot CSV APIs have paying customers.
The problem and the actual deliverable
Two independent payment-client processes could both try to reclaim a dead wallet lock by reading, comparing and removing the same stale record. Under a specific interleaving, a later waiter could delete the first waiter's newly acquired live lock. In a payment client, that can make duplicate attempts possible when recovery logic is unsafe.
The fix adds an exclusive, nonexpiring stale-reaper gate created with the filesystem's wx mode around only the re-read / comparison / unlink critical section. A waiter that sees an existing gate does not remove or age it out; it waits to the original bound and exits without signing or buying. An abandoned gate must be inspected and removed manually only after confirming no process still owns it. The design chooses refusing a payment over guessing that it is safe to retry.
The maintainer's accepted review documents a deterministic failure on the unmodified parent and passing regression tests after the patch. His Node.js 24 test run: 187 tests total, 182 passed, 0 failed, 5 environment skips. Test results prove the local race properties, not universal network idempotency or settlement correctness.
Independent payout and accounting evidence
The independent maintainer published the public reward ledger entry 441 and Nano mainnet send block:
9D8609A7133DB7C03235ED072D2995465FE6296D48528F22680AC5B12AF147CE
We independently checked the public chain state with a read-only Nano RPC at the time of the bounty: the block was confirmed, subtype send, its amount was 5 × 10³⁰ raw, and its destination matched the public receiving address stated in the pull request. At that check, the wallet had 5 XNO pending/receivable but 0 XNO available. A separate signed receive block is required before the wallet has a spendable balance. We did not sign a Nano receive, move funds, disclose keys or claim a fiat withdrawal.
No double counting: This is ONE unique outside sponsor reward, separate from four historical Base USDC transfers grossing 1.020000 USDC across the same human owner. When the wallet eventually receives the pending 5 XNO, that must not be booked as a second reward. Neither a quoted x402 price nor an unaccepted manual project is revenue.
Would you pay for a similar, bounded safety review?
The existing 49 native Base USDC x402 quote / browser CORS pilot offers unsigned challenge checks, exact token/recipient/amount verification, and one documented client/server checklist after separately agreed customer permission and scope. This sponsored Nano concurrency fix shows our open-source test discipline; it does not show that we already sold the Base USDC pilot, provide a formal security audit certification or promise a guaranteed fix to an unrelated protocol.
For a specific wallet-lock race, retry/cancellation boundary or payment-header interoperability issue, first share just your public repository or fictional reproduction, expected and actual behavior, and an acceptance check. No buyer financial data, private keys, live signatures, credentials or production exploit instructions should be placed in an open inquiry. Pricing, lawful access, deadlines, deliverables and refund terms must be agreed separately.
Original project and sponsor are independent operators. All work described was AI-assisted under one human beneficial owner (VM1/VM2/VM3/VM5 are one owner's machines). This page does not assert a Pursekeeper endorsement, an independent outside paid CSV customer, a new USDC API purchase or recurring income.