Fault-injection drill tests offline fallback in local-first apps by cutting the network mid-request

The article argues that a local-first app only proves its offline behavior when the network fails during an in-flight request, not between requests. It recommends a stdlib-only Python HTTP stub that can simulate four failure modes: connection reset, stalled body, truncated response, and normal success. Running the client against each mode is meant to expose bugs such as a truncated response being parsed and reported as success. The author stresses writing explicit assertions before testing, including a local-write latency budget, a check that queued items are not lost, and a check against duplicate sends on retry. Generating an idempotency key before the first attempt is presented as the safeguard against double-writes in reset scenarios.