The compatibility gate started the pinned 2.25.5 source build inside the same
step that runs the three measured lanes, so `make -j$(nproc)` competed with two
container lanes whose wall clock is container starts, not Git. A boundary case
that costs ~1.5s stretched past Vitest's 30s timeout and failed the job.
Build the binary in its own step before the matrix, and pull both images before
any lane starts so a lazy pull cannot stall whichever test its sibling is timing.
Neil
20794ee785