Internal replay benchmark for coding-agent changes in monorepos
Teams evaluating coding agents on production repositories can build an internal replay bench from real assistant sessions, landed diffs, and stable test subsets. ProdCodeBench shows the recipe in enough detail to copy: keep the original developer prompt, back out the landed change from current repo state, then grade candidate agents against repeated fail-to-pass and pass-to-pass test runs. The useful part is not only realism. It is speed. The paper positions this as a faster offline check for model swaps, harness changes, and infrastructure updates that would otherwise wait on slow A/B tests. A practical first version is narrow: one service, one language-heavy area of the monorepo, and only prompts that already have stable relevant tests. If that slice can reproduce relative model rankings across three reruns without heavy manual triage, it becomes a routine gate for agent releases.