Silent CI failure: stale binary passed 13 test suites after zero-second build

A software pipeline silently failed when its build step completed in zero seconds and reported success, having compiled nothing at all. The root cause was a mirror script that preserved original file timestamps when copying source code, causing the build tool to treat existing artifacts as newer than the freshly copied sources and skip recompilation entirely. Thirteen test suites then ran against the previous day's binary, each passing with byte-identical results — which the pipeline's own determinism checks ironically confirmed as correct. The build duration field logged 'seconds=0' throughout, signalling the failure openly, but no automated check was reading it. The fix involves resetting source file timestamps after mirroring, or better yet, asserting that either build time exceeds zero or all artifact timestamps post-date the mirror's start time.