Coding-Agent Verification: Idempotent Retry

A coding agent can make a retrying payment client look correct while it still charges twice after a lost response. I built a synthetic Python evaluation environment that judges the repair from a separate fake gateway's charge ledger, checks the public API and protected files, and emits PASS, FAIL or infrastructure ERROR with per-check evidence. Five scripted scenarios distinguish a correct per-order idempotency key from plausible shortcuts and test-file tampering.

Effect-based grading against gateway-recorded charges and receipt IDs

Deterministic faults before and after payment commit, gateway outage, and distinct-order checks

SHA-256 file locks and unexpected-file detection; API-shape and visible-test checks

Seven predeclared solution variants with exact expected verdicts and failing-check identities

Digest-pinned Docker configuration: network disabled, read-only mounts, dropped capabilities, resource limits and explicit runtime selection without fallback

Reviewed main commit 1224e644. In the October 1, 2026 review, the unmodified verifier was run directly with Python 3.12 against all seven supplied variants twice: one PASS, five expected FAILs, one expected infrastructure ERROR. Both fresh runs matched the committed evidence SHA-256 exactly: bc1d2f0d8676d0538a7cdfaf46c6be36ebf93791a11ee2159b56469d22a9474f.

Verifier source · Expected/observed matrix · Container harness

The repository also contains historical gVisor/runsc logs, matrices and hashes. Their fixture, verifier, matrix and evidence hashes were cross-checked. Docker/runsc was unavailable for a fresh container run in this review; the fresh rerun establishes verifier behavior, not renewed isolation validation.

Reproduce the repository's container workflow with: python3 harness/validate.py --repeat For the gVisor workflow: python3 harness/prove_gvisor.py

Self-directed synthetic sample, built with AI assistance; no paid client or production deployment claimed. Candidate and verifier share a container: the demonstrated file checks are not a defense against every hostile process attack. Concurrent retries and real payment systems are outside this fixture. Source is PolyForm Noncommercial; commercial reuse requires a separate license.

Hire me for a custom coding-agent eval suite with explicit failure cases, reproducible grading and inspectable regression evidence.